Initial commit.

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diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+samd21-demo.bin
+.gdb_history
+qemu.pid
+app/*.uf2
+*/target
+**/*.rs.bk
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
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+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1d2d59d
--- /dev/null
+++ b/README.md
@@ -0,0 +1,33 @@
+# SAMD21 demo
+
+This is mostly a proof-of-concept of a USB Host driver on the SAMD21
+platform.
+
+The code is also a complete mess, but is hopefully understandable
+enough. At some point I intend to separate this into architecture
+dependent and independent stuff with a HAL layer. However, right now,
+this is mostly just slapped together as I tried to figure out how to
+get stuff to work at all.
+
+# Features
+
+Basically none. It'll go through enumeration up to the point of
+assigning an address, but that's it right now. Short term priority is
+getting the system to a point where it can host a boot-protocol
+keyboard.
+
+# Board support
+
+Uses trinket-m0, but should be fairly easy to port to other samd
+architectures.
+
+# Building
+
+Normal cargo stuff works. There's a `Makefile` which has a target for
+flashing an Adafruit Trinket M0 on Linux.
+
+You'll need to tweak the atsamd-hal to remove the feature requirements
+for generating the USB padcal code. You'll also need to add
+definitions for the 1kHz SOF pad, and (optionally) the USB Host Enable
+PIN. You can find a version of the HAL that does this [on my github
+branch](https://github.com/bjc/atsamd/tree/unflag-usb-calibration).
diff --git a/app/.cargo/config b/app/.cargo/config
new file mode 100644
index 0000000..b6cdff0
--- /dev/null
+++ b/app/.cargo/config
@@ -0,0 +1,6 @@
+[build]
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+
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+runner = "qemu-system-arm -pidfile qemu.pid -cpu cortex-m0 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -gdb tcp::3333 -S -kernel"
diff --git a/app/Cargo.lock b/app/Cargo.lock
new file mode 100644
index 0000000..ca61229
--- /dev/null
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diff --git a/app/Cargo.toml b/app/Cargo.toml
new file mode 100644
index 0000000..fd96c1a
--- /dev/null
+++ b/app/Cargo.toml
@@ -0,0 +1,27 @@
+[package]
+name = "samd21-demo"
+version = "0.1.0"
+authors = ["Brian Cully <bjc@kublai.com>"]
+edition = "2018"
+readme = "../README.md"
+license = "GPL-3.0-or-later"
+license-file = "../COPYING"
+
+[dependencies]
+trinket_m0 = { path = "../../atsamd/boards/trinket_m0" }
+panic-halt = "~0.2"
+smart-leds = "~0.2"
+smart-leds-trait = "~0.2"
+apa102-spi = "~0.2" # DotStar driver.
+nb = "~0.1"
+cortex-m = "~0.6"
+cortex-m-rt = "~0.6"
+embedded-hal = "~0.2"
+clint = { path = "../../clint" }
+#cortex-m-semihosting = "~0.3"
+bare-metal = "~0.2"
+rb = { path = "../rb" }
+vcell = "~0.1"
+
+[features]
+default = ["cortex-m/const-fn"]
diff --git a/app/Makefile b/app/Makefile
new file mode 100644
index 0000000..a5ef39f
--- /dev/null
+++ b/app/Makefile
@@ -0,0 +1,38 @@
+APP = samd21-demo
+
+USBVID = 239a
+USBPID = '001e|801e'
+
+BOSSAC = bossac
+SERIAL = $(shell ./find-serial-port $(USBVID) $(USBPID) || echo 'cant-find-serial-port')
+OFFSET = 0x2000
+
+.PHONY: all clean cargo-build
+
+all: $(APP).uf2
+
+clean:
+	rm -f $(APP).uf2
+	rm -f $(APP).bin
+	cargo clean
+
+cargo-build:
+	cargo build
+
+target/thumbv6m-none-eabi/debug/$(APP): cargo-build
+
+$(APP).bin: target/thumbv6m-none-eabi/debug/$(APP)
+	cargo objcopy --bin $(APP) -- -O binary $(APP).bin
+
+# Requires https://github.com/sajattack/uf2conv-rs.git
+%.uf2: %.bin
+	uf2conv-rs $< --base $(OFFSET) --output $@
+
+flash: $(APP).bin $(SERIAL)
+	$(BOSSAC) -R -e -w -v -o$(OFFSET) -p$(SERIAL) $<
+
+qemu: target/thumbv6m-none-eabi/debug/$(APP)
+	qemu-system-arm -d in_asm,int,exec,cpu,guest_errors,unimp -pidfile qemu.pid -cpu cortex-m0 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -s -S -kernel $<
+
+gdb: target/thumbv6m-none-eabi/debug/$(APP)
+	gdb-multiarch -ex "target remote localhost:1234" -ex "break main" -ex "continue" $<
diff --git a/app/find-serial-port b/app/find-serial-port
new file mode 100755
index 0000000..62e2c0c
--- /dev/null
+++ b/app/find-serial-port
@@ -0,0 +1,16 @@
+#!/bin/sh
+
+if [ $# -ne 2 ]; then
+    echo "Usage: $0 vid pid" >&2
+    exit 1
+fi
+
+prefix=/dev/serial/by-id
+
+for dev in `ls $prefix`; do
+    if [ `udevadm info -q property --name $prefix/$dev | egrep -i "ID_VENDOR_ID=($1)|ID_MODEL_ID=($2)" | wc -l` -eq 2 ]; then
+        echo `readlink -f $prefix/$dev`
+        exit 0
+    fi
+done
+exit 2
diff --git a/app/samd21-demo.uf2 b/app/samd21-demo.uf2
new file mode 100644
index 0000000..035b8a5
--- /dev/null
+++ b/app/samd21-demo.uf2
diff --git a/app/src/dotstar.rs b/app/src/dotstar.rs
new file mode 100644
index 0000000..8e930d0
--- /dev/null
+++ b/app/src/dotstar.rs
@@ -0,0 +1,42 @@
+use trinket_m0::{
+    clock::GenericClockController,
+    gpio::{self, Floating, Input},
+    prelude::*,
+    sercom::{self, PadPin, SPIMaster1},
+    PM, SERCOM1,
+};
+
+use apa102_spi::Apa102;
+
+pub fn new(
+    sercom: SERCOM1,
+    miso: gpio::Pa31<Input<Floating>>,
+    mosi: gpio::Pa0<Input<Floating>>,
+    sck: gpio::Pa1<Input<Floating>>,
+    port: &mut gpio::Port,
+    pm: &mut PM,
+    clocks: &mut GenericClockController,
+) -> Apa102<
+    SPIMaster1<
+        sercom::Sercom1Pad3<gpio::Pa31<gpio::PfD>>,
+        sercom::Sercom1Pad0<gpio::Pa0<gpio::PfD>>,
+        sercom::Sercom1Pad1<gpio::Pa1<gpio::PfD>>,
+    >,
+> {
+    let gclk = clocks.gclk0();
+    let miso = miso.into_pad(port);
+    let mosi = mosi.into_pad(port);
+    let sck = sck.into_pad(port);
+    let spi = SPIMaster1::new(
+        &clocks
+            .sercom1_core(&gclk)
+            .expect("setting up sercom1 clock"),
+        3.mhz(),
+        apa102_spi::MODE,
+        sercom,
+        pm,
+        (miso, mosi, sck),
+    );
+
+    Apa102::new(spi)
+}
diff --git a/app/src/log.rs b/app/src/log.rs
new file mode 100644
index 0000000..6cfba8f
--- /dev/null
+++ b/app/src/log.rs
@@ -0,0 +1,95 @@
+use rb::{Reader, RingBuffer, Writer};
+
+use core::fmt::{self, Write};
+use embedded_hal::{digital::v2::OutputPin, serial};
+use trinket_m0::{
+    gpio::{Pa6, Pa7, PfD},
+    sercom::{Sercom0Pad2, Sercom0Pad3, UART0},
+};
+
+static mut LB: RingBuffer<u8> = RingBuffer::<u8>::new(0);
+
+struct JoinedRingBuffer<'a> {
+    lbr: Reader<'a, u8>,
+    lbw: Writer<'a, u8>,
+}
+
+impl<'a> JoinedRingBuffer<'a> {
+    const fn new(rb: &'a RingBuffer<u8>) -> Self {
+        let (lbr, lbw) = rb.split();
+        Self { lbr: lbr, lbw: lbw }
+    }
+}
+
+impl Write for JoinedRingBuffer<'_> {
+    fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
+        for b in s.bytes() {
+            if let Err(_) = self.lbw.unshift(b) {
+                // Ignore buffer full errors for logging.
+                return Ok(());
+            }
+        }
+        Ok(())
+    }
+}
+
+static mut LOGBUF: JoinedRingBuffer = unsafe { JoinedRingBuffer::new(&LB) };
+static mut UART0: usize = 0;
+
+pub struct Processor<W, L> {
+    uart: W,
+    led: L,
+}
+
+impl<W, L> Processor<W, L>
+where
+    W: serial::Write<u8>,
+    L: OutputPin,
+{
+    pub fn new(uart: W, led: L) -> Self {
+        // Unsafe because we're creating a mutable alias.
+        unsafe { UART0 = core::mem::transmute(&uart) };
+        Self {
+            uart: uart,
+            led: led,
+        }
+    }
+
+    pub fn task(&mut self) {
+        // Unsafe due to mutable static.
+        if unsafe { LOGBUF.lbr.is_empty() } {
+            return;
+        }
+        self.led.set_high().ok();
+        // Unsafe due to mutable static.
+        while let Some(b) = unsafe { LOGBUF.lbr.shift() } {
+            nb::block!(self.uart.write(b)).ok();
+        }
+        self.led.set_low().ok();
+    }
+}
+
+// Write to the UART right now, instead of putting it on a ring
+// buffer. This function is a huge hack, and only useful for debugging
+// either before the main loop starts or if the ring buffer is broken.
+pub unsafe fn write_fmt_now(args: fmt::Arguments, nl: bool) {
+    if UART0 == 0 {
+        return;
+    }
+    let uart: &mut UART0<Sercom0Pad3<Pa7<PfD>>, Sercom0Pad2<Pa6<PfD>>, (), ()> =
+        core::mem::transmute(UART0);
+    fmt::write(uart, args).expect("writing fmt now to uart");
+    if nl {
+        uart.write_str("\r\n").expect("writing nl now to uart");
+    }
+}
+
+pub fn write_fmt(args: fmt::Arguments, nl: bool) {
+    // Unsafe due to mutable static.
+    unsafe {
+        fmt::write(&mut LOGBUF, args).expect("writing fmt to log");
+        if nl {
+            LOGBUF.write_str("\r\n").expect("writing nl to log");
+        }
+    }
+}
diff --git a/app/src/macros.rs b/app/src/macros.rs
new file mode 100644
index 0000000..fe262b4
--- /dev/null
+++ b/app/src/macros.rs
@@ -0,0 +1,31 @@
+#[macro_export]
+macro_rules! logln {
+    ($($arg:tt)*) => {
+        crate::log::write_fmt(format_args!($($arg)*), true);
+    };
+    (_) => {};
+}
+
+#[macro_export]
+macro_rules! log {
+    ($($arg:tt)*) => {
+        crate::log::write_fmt(format_args!($($arg)*), false);
+    };
+    (_) => {};
+}
+
+#[macro_export]
+macro_rules! logln_now {
+    ($($arg:tt)*) => {
+        unsafe {crate::log::write_fmt_now(format_args!($($arg)*), true);}
+    };
+    (_) => {};
+}
+
+#[macro_export]
+macro_rules! log_now {
+    ($($arg:tt)*) => {
+        unsafe {crate::log::write_fmt_now(format_args!($($arg)*), false);}
+    };
+    (_) => {};
+}
diff --git a/app/src/main.rs b/app/src/main.rs
new file mode 100755
index 0000000..1025fae
--- /dev/null
+++ b/app/src/main.rs
@@ -0,0 +1,202 @@
+#![no_std]
+#![no_main]
+#![feature(const_fn)]
+#![feature(const_transmute)]
+#![allow(dead_code)]
+
+mod dotstar;
+mod log;
+mod macros;
+mod rtc;
+mod usb;
+
+//#[allow(unused)]
+//use panic_halt;
+
+use clint::HandlerArray;
+use cortex_m::asm::wfi;
+use cortex_m_rt::{entry, exception, ExceptionFrame};
+use embedded_hal::digital::v2::OutputPin;
+use smart_leds::colors;
+use smart_leds_trait::SmartLedsWrite;
+use trinket_m0::{
+    self as hal,
+    clock::GenericClockController,
+    gpio::{OpenDrain, Output, Pa10},
+    target_device::{interrupt, Interrupt},
+    time::*,
+    CorePeripherals, Peripherals,
+};
+
+static HANDLERS: HandlerArray = HandlerArray::new();
+
+static mut LED: usize = 0;
+
+#[entry]
+fn main() -> ! {
+    let mut peripherals = Peripherals::take().expect("taking peripherals");
+    let mut core = CorePeripherals::take().expect("taking core peripherals");
+
+    let mut clocks = GenericClockController::with_internal_32kosc(
+        peripherals.GCLK,
+        &mut peripherals.PM,
+        &mut peripherals.SYSCTRL,
+        &mut peripherals.NVMCTRL,
+    );
+
+    let mut pins = hal::Pins::new(peripherals.PORT);
+
+    let uart = hal::uart(
+        &mut clocks,
+        115_200.hz(),
+        peripherals.SERCOM0,
+        &mut core.NVIC,
+        &mut peripherals.PM,
+        pins.d3,
+        pins.d4,
+        &mut pins.port,
+    );
+
+    let mut red_led = pins.d13.into_open_drain_output(&mut pins.port);
+    red_led.set_low().expect("turning off red LED");
+    unsafe { LED = core::mem::transmute(&red_led) }
+
+    let mut processor = log::Processor::new(uart, red_led);
+    logln_now!("setting up dotstar");
+
+    let mut dotstar = dotstar::new(
+        peripherals.SERCOM1,
+        pins.swdio,
+        pins.dotstar_di,
+        pins.dotstar_ci,
+        &mut pins.port,
+        &mut peripherals.PM,
+        &mut clocks,
+    );
+
+    let black = [colors::BLACK];
+    let blue = [colors::DARK_MAGENTA];
+
+    logln_now!("setting up timer");
+    let mut rtc_handler = rtc::setup(peripherals.RTC, &mut clocks);
+
+    logln_now!("setting up usb host");
+    let (mut usb_host, mut usb_handler) = usb::USBHost::new(
+        peripherals.USB,
+        pins.usb_sof,
+        pins.usb_dm,
+        pins.usb_dp,
+        Some(pins.usb_host_enable),
+        &mut pins.port,
+        &mut clocks,
+        &mut peripherals.PM,
+    );
+
+    logln!("setting up handlers");
+    HANDLERS.with_overrides(|hs| {
+        hs.register(0, &mut rtc_handler);
+        core.NVIC.enable(Interrupt::RTC);
+
+        hs.register(1, &mut usb_handler);
+        unsafe { core.NVIC.set_priority(Interrupt::USB, 0) };
+        core.NVIC.enable(Interrupt::USB);
+
+        logln!("Boot up complete.");
+
+        let mut last_tick = 0;
+        loop {
+            dotstar
+                .write(black.iter().cloned())
+                .expect("turning off dotstar");
+
+            let tick = rtc::millis();
+            if tick >= last_tick + 1_024 {
+                last_tick = tick;
+                //logln!("{}: tick", rtc::millis());
+            }
+
+            usb_host.task();
+
+            processor.task();
+
+            dotstar
+                .write(blue.iter().cloned())
+                .expect("turning on dotstar");
+            wfi();
+        }
+    });
+    unreachable!();
+}
+
+#[panic_handler]
+fn panic_handler(pi: &core::panic::PanicInfo) -> ! {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("~~~ PANIC ~~~");
+    logln_now!("{}", pi);
+    loop {
+        wfi()
+    }
+}
+
+#[exception]
+fn HardFault(ef: &ExceptionFrame) -> ! {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("!!! Hard Fault - ef: {:?} !!!", ef);
+    loop {
+        wfi()
+    }
+}
+
+#[exception]
+fn DefaultHandler(interrupt: i16) {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("*** Default Handler: {} ***", interrupt);
+}
+
+#[exception]
+fn NonMaskableInt() {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("+++ NonMaskableInt +++");
+}
+
+#[exception]
+fn SVCall() {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("+++ SVCall +++");
+}
+
+#[exception]
+fn PendSV() {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("+++ PendSV +++");
+}
+
+#[exception]
+fn SysTick() {
+    let red_led: &mut Pa10<Output<OpenDrain>> = unsafe { core::mem::transmute(LED) };
+    red_led.set_high().ok();
+
+    logln_now!("+++ SysTick +++");
+}
+
+#[interrupt]
+fn RTC() {
+    HANDLERS.call(0);
+}
+
+#[interrupt]
+fn USB() {
+    HANDLERS.call(1);
+}
diff --git a/app/src/rtc.rs b/app/src/rtc.rs
new file mode 100644
index 0000000..0d39d31
--- /dev/null
+++ b/app/src/rtc.rs
@@ -0,0 +1,71 @@
+use core::sync::atomic::{AtomicUsize, Ordering};
+use trinket_m0::{clock::GenericClockController, RTC};
+
+struct Clock(AtomicUsize);
+impl Clock {
+    const fn new() -> Self {
+        Self(AtomicUsize::new(0))
+    }
+
+    fn set(&self, millis: usize) {
+        self.0.store(millis, Ordering::SeqCst)
+    }
+
+    // Slightly less than 1ms, due to using a 32,768Hz clock, we can't
+    // hit exactly 1ms, so we shoot for a bit under.
+    fn millis(&self) -> usize {
+        self.0.load(Ordering::SeqCst)
+    }
+}
+
+static CLOCK: Clock = Clock::new();
+
+// Set to run every ~500µs.
+static COUNTER: u32 = 16; // 32 ticks requires 1024 cycles at 32,768Hz for 1 second.
+
+pub fn setup(mut rtc: RTC, clocks: &mut GenericClockController) -> impl FnMut() {
+    let rtc_clock = &clocks.gclk1();
+    clocks.rtc(&rtc_clock);
+
+    rtc.mode0().ctrl.write(|w| w.swrst().set_bit());
+    while rtc.mode0().status.read().syncbusy().bit_is_set() {}
+
+    rtc.mode0().ctrl.write(|w| {
+        w.mode().count32();
+
+        // Neither the prescaler nor matchlr values seem to work. Not
+        // sure why.
+        //w.prescaler().div1024();
+        w.matchclr().set_bit() // Reset on match for periodic
+    });
+
+    rtc.mode0().comp[0].write(|w| unsafe { w.bits(COUNTER) });
+    rtc.mode0().intflag.write(|w| w.cmp0().set_bit());
+    rtc.mode0().intenset.write(|w| w.cmp0().set_bit());
+
+    // Enable the RTC and wait for sync.
+    rtc.mode0().ctrl.write(|w| w.enable().set_bit());
+    while rtc.mode0().status.read().syncbusy().bit_is_set() {}
+
+    move || handler(&mut rtc)
+}
+
+pub fn millis() -> usize {
+    CLOCK.millis()
+}
+
+fn handler(rtc: &mut RTC) {
+    // FIXME: matchclr doesn't seem to work to reset the counter?
+    rtc.mode0().count.write(|w| unsafe { w.bits(0) });
+    rtc.mode0().intflag.write(|w| w.cmp0().set_bit());
+
+    static mut TICKS: usize = 0;
+    static mut ADD: bool = false;
+    unsafe {
+        if ADD {
+            TICKS += 1;
+            CLOCK.set(TICKS);
+        }
+        ADD = !ADD;
+    }
+}
diff --git a/app/src/usb.rs b/app/src/usb.rs
new file mode 100644
index 0000000..c15e1b5
--- /dev/null
+++ b/app/src/usb.rs
@@ -0,0 +1,612 @@
+mod pipe;
+mod usbproto;
+
+use crate::{log, logln, logln_now, rtc};
+use pipe::{DataBuf, PipeErr, PipeTable, USBPipeType, USBToken};
+use rb::{Reader, RingBuffer, Writer};
+use usbproto::*;
+
+use embedded_hal::digital::v2::OutputPin;
+use trinket_m0::{
+    calibration::{usb_transn_cal, usb_transp_cal, usb_trim_cal},
+    clock::{ClockGenId, ClockSource, GenericClockController},
+    gpio::{self, Floating, Input, OpenDrain, Output},
+    PM, USB,
+};
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Event {
+    Error,
+    Detached,
+    Attached,
+}
+type Events = RingBuffer<Event>;
+type EventReader = Reader<'static, Event>;
+type EventWriter = Writer<'static, Event>;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+enum DetachedState {
+    Initialize,
+    WaitForDevice,
+    Illegal,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+enum AttachedState {
+    WaitForSettle,
+    WaitResetComplete,
+    WaitSOF,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+enum SteadyState {
+    Configuring,
+    Running,
+    Error,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+enum TaskState {
+    Detached(DetachedState),
+    Attached(AttachedState),
+    Steady(SteadyState),
+}
+
+const MAX_DEVICES: usize = 16;
+const SETTLE_DELAY: usize = 205; // Delay in sec/1024
+const NAK_LIMIT: usize = 15;
+
+static mut EVENTS: Events = Events::new(Event::Error);
+// FIXME: this is just for testing. The enum needs to be
+// thread-safe if this is the way we're going.
+static mut LATEST_EVENT: Event = Event::Detached;
+
+#[repr(C)]
+#[derive(Debug)]
+struct EPInfo {
+    ep_addr: u32,
+    mak_pkt_size: u32,
+    ep_attribs: u8,
+}
+
+impl EPInfo {
+    fn bm_snd_toggle(&self) -> bool {
+        const POS: u8 = 0;
+        const MASK: u8 = 0x1;
+        ((self.ep_attribs >> POS) & MASK) == 1
+    }
+    fn bm_rcv_toggle(&self) -> bool {
+        const POS: u8 = 1;
+        const MASK: u8 = 0x1;
+        ((self.ep_attribs >> POS) & MASK) == 1
+    }
+    fn bm_nak_power(&self) -> u8 {
+        const POS: u8 = 2;
+        const MASK: u8 = 0x3f;
+        (self.ep_attribs >> POS) & MASK
+    }
+}
+
+#[derive(Debug)]
+struct USBDeviceAddress(u32);
+
+impl USBDeviceAddress {
+    fn bm_address(&self) -> u8 {
+        const POS: u8 = 0;
+        const MASK: u32 = 0x7;
+        ((self.0 >> POS) & MASK) as u8
+    }
+    fn bm_parent(&self) -> u8 {
+        const POS: u8 = 3;
+        const MASK: u32 = 0x7;
+        ((self.0 >> POS) & MASK) as u8
+    }
+    fn bm_hub(&self) -> bool {
+        const POS: u8 = 6;
+        const MASK: u32 = 0x1;
+        ((self.0 >> POS) & MASK) == 1
+    }
+}
+
+pub struct USBHost {
+    usb: USB,
+
+    events: EventReader,
+    task_state: TaskState,
+    delay: usize,
+
+    // Need chunk of RAM for USB pipes, which gets used with DESCADD
+    // register.
+    pipe_table: PipeTable,
+
+    // need sof 1kHz pad?
+    _sof_pad: gpio::Pa23<gpio::PfG>,
+    _dm_pad: gpio::Pa24<gpio::PfG>,
+    _dp_pad: gpio::Pa25<gpio::PfG>,
+    host_enable_pin: Option<gpio::Pa28<Output<OpenDrain>>>,
+}
+
+impl USBHost {
+    pub fn new(
+        usb: USB,
+        sof_pin: gpio::Pa23<Input<Floating>>,
+        dm_pin: gpio::Pa24<Input<Floating>>,
+        dp_pin: gpio::Pa25<Input<Floating>>,
+        host_enable_pin: Option<gpio::Pa28<Input<Floating>>>,
+        port: &mut gpio::Port,
+        clocks: &mut GenericClockController,
+        pm: &mut PM,
+    ) -> (Self, impl FnMut()) {
+        let (eventr, mut eventw) = unsafe { EVENTS.split() };
+        let mut rc = Self {
+            usb: usb,
+            events: eventr,
+            task_state: TaskState::Detached(DetachedState::Initialize),
+            delay: 0,
+            pipe_table: PipeTable::new(),
+
+            _sof_pad: sof_pin.into_function_g(port),
+            _dm_pad: dm_pin.into_function_g(port),
+            _dp_pad: dp_pin.into_function_g(port),
+            host_enable_pin: None,
+        };
+
+        if let Some(he_pin) = host_enable_pin {
+            rc.host_enable_pin = Some(he_pin.into_open_drain_output(port));
+        }
+
+        logln_now!("setting up usb clock");
+        pm.apbbmask.modify(|_, w| w.usb_().set_bit());
+
+        // Set up USB clock from 48MHz source on generic clock 6.
+        clocks.configure_gclk_divider_and_source(ClockGenId::GCLK6, 1, ClockSource::DFLL48M, false);
+        let gclk6 = clocks
+            .get_gclk(ClockGenId::GCLK6)
+            .expect("Could not get clock 6");
+        clocks.usb(&gclk6);
+
+        rc.reset_periph();
+
+        let usbp = &rc.usb as *const _ as usize;
+        (rc, move || handler(usbp, &mut eventw))
+    }
+
+    pub fn reset_periph(&mut self) {
+        log!("resetting usb");
+        // Reset the USB peripheral and wait for sync.
+        self.usb.host().ctrla.write(|w| w.swrst().set_bit());
+        while self.usb.host().syncbusy.read().swrst().bit_is_set() {}
+
+        // Specify host mode.
+        self.usb.host().ctrla.modify(|_, w| w.mode().host());
+
+        // Unsafe due to use of raw bits method.
+        unsafe {
+            self.usb.host().padcal.write(|w| {
+                w.transn().bits(usb_transn_cal());
+                w.transp().bits(usb_transp_cal());
+                w.trim().bits(usb_trim_cal())
+            });
+        }
+
+        // Use normal, which is 0 and apparently means low-and-full capable
+        self.usb.host().ctrlb.modify(|_, w| w.spdconf().normal());
+        // According to docs, 1,2,3 are reserved, but .fs returns 3
+        //self.usb.host().ctrlb.modify(|_, w| w.spdconf().fs());
+
+        self.usb.host().ctrla.modify(|_, w| w.runstdby().set_bit()); // keep usb clock running in standby.
+
+        // Set address of USB SRAM.
+        // Unsafe due to use of raw bits method.
+        unsafe {
+            self.usb
+                .host()
+                .descadd
+                .write(|w| w.bits(&self.pipe_table as *const _ as u32));
+        }
+
+        if let Some(he_pin) = &mut self.host_enable_pin {
+            he_pin.set_high().expect("turning on usb host enable pin");
+        }
+
+        self.usb.host().intenset.write(|w| {
+            w.wakeup().set_bit();
+            w.dconn().set_bit();
+            w.ddisc().set_bit()
+        });
+
+        self.usb.host().ctrla.modify(|_, w| w.enable().set_bit());
+        while self.usb.host().syncbusy.read().enable().bit_is_set() {}
+
+        // Set VBUS OK to allow host operation.
+        self.usb.host().ctrlb.modify(|_, w| w.vbusok().set_bit());
+        logln!("...done");
+    }
+
+    pub fn task(&mut self) {
+        static mut LAST_EVENT: Event = Event::Error;
+        unsafe {
+            if LAST_EVENT != LATEST_EVENT {
+                logln!("new event: {:?}", LATEST_EVENT);
+            }
+        }
+
+        static mut LAST_TASK_STATE: TaskState = TaskState::Detached(DetachedState::Illegal);
+        self.task_state = match unsafe { LATEST_EVENT } {
+            Event::Error => TaskState::Detached(DetachedState::Illegal),
+            Event::Detached => {
+                if let TaskState::Detached(_) = self.task_state {
+                    self.task_state
+                } else {
+                    TaskState::Detached(DetachedState::Initialize)
+                }
+            }
+            Event::Attached => {
+                if let TaskState::Detached(_) = self.task_state {
+                    self.delay = rtc::millis() + SETTLE_DELAY;
+                    TaskState::Attached(AttachedState::WaitForSettle)
+                } else {
+                    self.task_state
+                }
+            }
+        };
+
+        static mut LAST_CBITS: u16 = 0;
+        static mut LAST_FLAGS: u16 = 0;
+        let cbits = self.usb.host().ctrlb.read().bits();
+        let bits = self.usb.host().intflag.read().bits();
+        unsafe {
+            if LAST_CBITS != cbits || LAST_FLAGS != bits || LAST_TASK_STATE != self.task_state {
+                logln!(
+                    "cb: {:x}, f: {:x} changing state {:?} -> {:?}",
+                    cbits,
+                    bits,
+                    LAST_TASK_STATE,
+                    self.task_state,
+                );
+            }
+            LAST_CBITS = cbits;
+            LAST_FLAGS = bits;
+            LAST_TASK_STATE = self.task_state
+        };
+
+        if let Some(_event) = self.events.shift() {
+            // logln!("Found event: {:?}", event);
+            // self.task_state = match event {
+            //     Event::None => TaskState::Detached(DetachedState::Illegal),
+            //     Event::Detached => {
+            //         if let TaskState::Detached(_) = self.task_state {
+            //             self.task_state
+            //         } else {
+            //             TaskState::Detached(DetachedState::Initialize)
+            //         }
+            //     }
+            //     Event::Attached => {
+            //         if let TaskState::Detached(_) = self.task_state {
+            //             self.delay = rtc::millis() + SETTLE_DELAY;
+            //             TaskState::Attached(AttachedState::WaitForSettle)
+            //         } else {
+            //             self.task_state
+            //         }
+            //     }
+            // };
+        }
+
+        self.poll_devices();
+        self.fsm();
+
+        unsafe {
+            LAST_EVENT = LATEST_EVENT;
+        }
+    }
+
+    fn poll_devices(&mut self) {
+        for _ in 0..MAX_DEVICES {}
+    }
+
+    fn fsm(&mut self) {
+        // respond to events from interrupt.
+        match self.task_state {
+            TaskState::Detached(s) => self.detached_fsm(s),
+            TaskState::Attached(s) => self.attached_fsm(s),
+            TaskState::Steady(s) => self.steady_fsm(s),
+        };
+    }
+
+    fn detached_fsm(&mut self, s: DetachedState) {
+        match s {
+            DetachedState::Initialize => {
+                self.reset_periph();
+                // TODO: Free resources.
+
+                self.task_state = TaskState::Detached(DetachedState::WaitForDevice);
+            }
+
+            // Do nothing state. Just wait for an interrupt to come in
+            // saying we have a device attached.
+            DetachedState::WaitForDevice => {}
+
+            // TODO: should probably reset everything if we end up here somehow.
+            DetachedState::Illegal => {}
+        }
+    }
+
+    fn attached_fsm(&mut self, s: AttachedState) {
+        match s {
+            AttachedState::WaitForSettle => {
+                if rtc::millis() >= self.delay {
+                    self.usb.host().ctrlb.modify(|_, w| w.busreset().set_bit());
+                    self.task_state = TaskState::Attached(AttachedState::WaitResetComplete);
+                }
+            }
+
+            AttachedState::WaitResetComplete => {
+                if self.usb.host().intflag.read().rst().bit_is_set() {
+                    logln!("reset was sent");
+                    self.usb.host().intflag.write(|w| w.rst().set_bit());
+
+                    // Make sure we always have a control pipe set up.
+                    self.init_pipe0();
+
+                    // Seems unneccesary, since SOFE will be set
+                    // immediately after reset according to §32.6.3.3.
+                    self.usb.host().ctrlb.modify(|_, w| w.sofe().set_bit());
+                    // USB spec requires 20ms of SOF after bus reset.
+                    self.delay = rtc::millis() + 20;
+                    self.task_state = TaskState::Attached(AttachedState::WaitSOF);
+                }
+            }
+
+            AttachedState::WaitSOF => {
+                if self.usb.host().intflag.read().hsof().bit_is_set() {
+                    self.usb.host().intflag.write(|w| w.hsof().set_bit());
+                    if rtc::millis() >= self.delay {
+                        self.task_state = TaskState::Steady(SteadyState::Configuring);
+                    }
+                }
+            }
+        }
+    }
+
+    fn steady_fsm(&mut self, s: SteadyState) {
+        match s {
+            SteadyState::Configuring => {
+                let low_speed = 0;
+                self.task_state = match self.configure_dev(0, 0, low_speed) {
+                    Ok(_) => TaskState::Steady(SteadyState::Running),
+                    Err(e) => {
+                        logln!("Enumeration error: {:?}", e);
+                        TaskState::Steady(SteadyState::Error)
+                    }
+                }
+            }
+
+            SteadyState::Running => {}
+
+            SteadyState::Error => {}
+        }
+    }
+
+    fn configure_dev(&mut self, _parent: u32, _port: u32, _low_speed: u32) -> Result<(), PipeErr> {
+        // addr: 0x20007774
+        let tmp: USBDeviceDescriptor = Default::default();
+        // addr: 0x20007788
+        let vol_descr = ::vcell::VolatileCell::new(tmp);
+        self.control_req(
+            0,
+            0,
+            BMRequestType::get_descr(),
+            USBRequest::GetDescriptor,
+            WValue::from((0, USBDescriptor::Device as u8)),
+            0,
+            Some(DataBuf::from(&vol_descr)),
+        )?;
+
+        let desc = vol_descr.get();
+        logln_now!(
+            " -- len: {}, ver: {:04x}, bMaxPacketSize: {}, bNumConfigurations: {}",
+            desc.b_length,
+            desc.bcd_usb,
+            desc.b_max_packet_size,
+            desc.b_num_configurations
+        );
+        logln_now!(" -- vid: {:x}, pid: {:x}", desc.id_vendor, desc.id_product);
+
+        // Assign address to this device and:
+        //  - Stash bMaxPacketSize
+        // Then SET_ADDRESS(newAddr)
+        let new_address: u8 = 1;
+        self.control_req(
+            0,
+            0,
+            BMRequestType::set(),
+            USBRequest::SetAddress,
+            WValue::from((new_address, 0)),
+            0,
+            None,
+        )?;
+        logln_now!(" -- address set");
+        // Delay according to §9.2.6.3 of USB 2.0
+        let until = rtc::millis() + 300;
+        while rtc::millis() < until {}
+
+        // Once addressed, SET_CONFIGURATION(0)
+        logln_now!("+++ setting configuration");
+        let conf: u8 = 0;
+        self.control_req(
+            new_address,
+            0,
+            BMRequestType::set(),
+            USBRequest::SetConfiguration,
+            WValue::from((conf, 0)),
+            0,
+            None,
+        )?;
+        logln_now!(" -- configuration set");
+
+        // Now we should be able to access it normally.
+
+        Ok(())
+    }
+
+    fn control_req(
+        &mut self,
+        addr: u8,
+        ep: u8,
+        bm_request_type: BMRequestType,
+        b_request: USBRequest,
+        w_value: WValue,
+        w_index: u16,
+        buf: Option<DataBuf>,
+    ) -> Result<(), PipeErr> {
+        if let Some(ref b) = buf {
+            assert!(b.ptr as usize & 0x3 == 0);
+            assert!(b.len <= 65_535);
+        }
+
+        /*
+         * Setup stage.
+         */
+        let setup_packet = USBSetupPacket {
+            bm_request_type: bm_request_type,
+            b_request: b_request,
+            w_value: w_value,
+            w_index: w_index,
+            w_length: match buf {
+                None => 0,
+                Some(ref b) => b.len as u16,
+            },
+        };
+        let mut pipe = self.pipe_table.pipe_for(self.usb.host_mut(), addr, ep);
+        pipe.send(USBToken::Setup, &DataBuf::from(&setup_packet), NAK_LIMIT)?;
+
+        /*
+         * Data stage.
+         */
+        if let Some(b) = buf {
+            match bm_request_type.direction() {
+                USBSetupDirection::DeviceToHost => {
+                    logln_now!("buf0: {:?}", &b);
+                    pipe.in_transfer(&b, NAK_LIMIT)?;
+                    logln_now!("buf1: {:?}", &b);
+                }
+
+                USBSetupDirection::HostToDevice => {
+                    logln_now!("Should OUT for {}b", b.len);
+                }
+            }
+        }
+
+        /*
+         * Status stage.
+         */
+        pipe.desc.bank0.pcksize.write(|w| {
+            // FIXME: see note in `Pipe.send`.
+            unsafe { w.bits(0) }
+        });
+
+        // PSTATUSSET.DTGL set -- TODO: figure out if this is
+        // necessary.
+        pipe.regs.statusset.write(|w| w.dtgl().set_bit());
+
+        let token = match bm_request_type.direction() {
+            USBSetupDirection::DeviceToHost => USBToken::Out,
+            USBSetupDirection::HostToDevice => USBToken::In,
+        };
+
+        // TODO: should probably make `pipe.send` have optional
+        // `DataBuf`, rather than exposing `dispatch_retries`.
+        logln_now!("dispatching status stage");
+        pipe.dispatch_retries(token, NAK_LIMIT)?;
+        Ok(())
+    }
+
+    // Set up a default pipe for the control endpoint 0 on pipe 0.
+    fn init_pipe0(&mut self) {
+        let speed = self.usb.host().status.read().speed().bits();
+        let pipe = self.pipe_table.pipe_for(self.usb.host_mut(), 0, 0);
+        pipe.regs.cfg.write(|w| {
+            unsafe { w.ptype().bits(USBPipeType::Control as u8) };
+            w.bk().clear_bit()
+        });
+        pipe.desc.bank0.pcksize.write(|w| match speed {
+            0 => w.size().bytes64(),
+            _ => w.size().bytes8(),
+        });
+    }
+}
+
+pub fn handler(usbp: usize, events: &mut EventWriter) {
+    let usb: &mut USB = unsafe { core::mem::transmute(usbp) };
+    let flags = usb.host().intflag.read();
+
+    logln!("USB - {:x}", flags.bits());
+
+    let mut unshift_event = |e: Event| {
+        unsafe { LATEST_EVENT = e };
+        if let Err(_) = events.unshift(e) {
+            logln!("Couldn't write USB event to queue.");
+        }
+    };
+
+    if flags.hsof().bit_is_set() {
+        logln!(" +hsof");
+        usb.host().intflag.write(|w| w.hsof().set_bit());
+        unshift_event(Event::Attached);
+    }
+
+    if flags.rst().bit_is_set() {
+        // We seem to get this whenever a device attaches/detaches.
+        logln!(" +rst");
+        usb.host().intflag.write(|w| w.rst().set_bit());
+        unshift_event(Event::Detached);
+    }
+
+    if flags.uprsm().bit_is_set() {
+        logln!(" +uprsm");
+        usb.host().intflag.write(|w| w.uprsm().set_bit());
+        unshift_event(Event::Detached);
+    }
+
+    if flags.dnrsm().bit_is_set() {
+        logln!(" +dnrsm");
+        usb.host().intflag.write(|w| w.dnrsm().set_bit());
+        unshift_event(Event::Detached);
+    }
+
+    if flags.wakeup().bit_is_set() {
+        // §32.8.5.8 - since VBUSOK is set, then this happens when a
+        // device is connected.
+        logln!(" +wakeup");
+        usb.host().intflag.write(|w| w.wakeup().set_bit());
+        unshift_event(Event::Attached);
+    }
+
+    if flags.ramacer().bit_is_set() {
+        logln!(" +ramacer");
+        usb.host().intflag.write(|w| w.ramacer().set_bit());
+        unshift_event(Event::Detached);
+    }
+
+    if flags.dconn().bit_is_set() {
+        logln!(" +dconn");
+        usb.host().intflag.write(|w| w.dconn().set_bit());
+        usb.host().intenclr.write(|w| w.dconn().set_bit());
+        usb.host().intflag.write(|w| w.ddisc().set_bit());
+        usb.host().intenset.write(|w| w.ddisc().set_bit());
+        usb.host().intflag.write(|w| w.dconn().set_bit());
+        unshift_event(Event::Attached);
+    }
+
+    if flags.ddisc().bit_is_set() {
+        logln!(" +ddisc");
+        usb.host().intflag.write(|w| w.ddisc().set_bit());
+        usb.host().intenclr.write(|w| w.ddisc().set_bit());
+        //			// Stop reset signal, in case of disconnection during reset
+        //			uhd_stop_reset(); // nothing on samd21
+        usb.host().intflag.write(|w| w.dconn().set_bit());
+        usb.host().intenset.write(|w| w.dconn().set_bit());
+        usb.host().intflag.write(|w| w.ddisc().set_bit());
+        unshift_event(Event::Detached);
+    }
+}
diff --git a/app/src/usb/pipe.rs b/app/src/usb/pipe.rs
new file mode 100644
index 0000000..12ca4cb
--- /dev/null
+++ b/app/src/usb/pipe.rs
@@ -0,0 +1,503 @@
+pub mod addr;
+pub mod ctrl_pipe;
+pub mod ext_reg;
+pub mod pck_size;
+pub mod status_bk;
+pub mod status_pipe;
+
+use addr::Addr;
+use ctrl_pipe::CtrlPipe;
+use ext_reg::ExtReg;
+use pck_size::PckSize;
+use status_bk::StatusBk;
+use status_pipe::StatusPipe;
+
+use crate::logln_now;
+use crate::rtc;
+
+use core::convert::TryInto;
+
+// FIXME: this stuff is needed for PipeRegs, and while tied to samd,
+// it shouldn't be tied to trinket_m0. Will need to figure out a
+// better layout for this.
+use trinket_m0::usb::{
+    self,
+    host::{BINTERVAL, PCFG, PINTFLAG, PSTATUS, PSTATUSCLR, PSTATUSSET},
+};
+
+// TODO: verify this timeout against §9.2.6.1 of USB 2.0 spec.
+const USB_TIMEOUT: usize = 5 * 1024; // 5 Seconds
+
+// samd21 only supports 8 pipes.
+const MAX_PIPES: usize = 8;
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub(crate) enum PipeErr {
+    InvalidPipe,
+    InvalidToken,
+    Stall,
+    TransferFail,
+    Flow,
+    HWTimeout,
+    DataToggle,
+    SWTimeout,
+    Other,
+}
+pub(crate) struct PipeTable {
+    tbl: [PipeDesc; MAX_PIPES],
+}
+
+impl PipeTable {
+    pub(crate) fn new() -> Self {
+        Self {
+            tbl: [PipeDesc::new(); MAX_PIPES],
+        }
+    }
+
+    pub(crate) fn pipe_for<'a, 'b>(
+        &'a mut self,
+        host: &'b mut usb::HOST,
+        addr: u8,
+        ep: u8,
+    ) -> Pipe<'a, 'b> {
+        // Just use two pipes for now. 0 is always for control
+        // endpoints, 1 for everything else.
+        //
+        // TODO: cache in-use pipes and return them without init if
+        // possible.
+        let i = if ep == 0 { 0 } else { 1 };
+
+        let pregs = PipeRegs::from(host, i);
+        let pdesc = &mut self.tbl[i];
+
+        logln_now!("setting paddr of pipe {} to {}:{}", i, addr, ep);
+        logln_now!("cpipe0: {:x}", pdesc.bank0.ctrl_pipe.read().bits());
+        pdesc.bank0.ctrl_pipe.write(|w| {
+            w.pdaddr().set_addr(addr);
+            w.pepnum().set_epnum(ep)
+        });
+        logln_now!("cpipe1: {:x}", pdesc.bank0.ctrl_pipe.read().bits());
+        Pipe {
+            num: i,
+            regs: pregs,
+            desc: pdesc,
+        }
+    }
+}
+
+// TODO: hide regs/desc fields. Needed right now for init_pipe0.
+pub(crate) struct Pipe<'a, 'b> {
+    num: usize,
+    pub(crate) regs: PipeRegs<'b>,
+    pub(crate) desc: &'a mut PipeDesc,
+}
+impl Pipe<'_, '_> {
+    pub(crate) fn send(
+        &mut self,
+        token: USBToken,
+        buf: &DataBuf,
+        nak_limit: usize,
+    ) -> Result<(), PipeErr> {
+        // Data needs to be word aligned.
+        assert!((buf.ptr as u32) & 0x3 == 0);
+        // byte_count section of register is 14 bits.
+        assert!(buf.len < 16_384);
+
+        logln_now!("p{}: sending {:?}", self.num, buf);
+
+        // Equiv to UHD_Pipe_Write(epAddr: 0, sizeof(setup_packet), &setup_packet)
+        self.desc
+            .bank0
+            .addr
+            .write(|w| unsafe { w.addr().bits(buf.ptr as u32) });
+        // configure packet size PCKSIZE.SIZE
+        self.desc.bank0.pcksize.write(|w| {
+            // FIXME: write raw to pcksize, because byte_count offset
+            // may be off? Doc table shows 6 bits, but text says 14,
+            // and arduino shows 14.
+            unsafe { w.bits(buf.len as u32) }
+            //unsafe { w.byte_count().bits(buf.len as u8) };
+            //unsafe { w.multi_packet_size().bits(0) }
+        });
+
+        self.dispatch_retries(token, nak_limit)
+    }
+
+    pub(crate) fn in_transfer(&mut self, buf: &DataBuf, nak_limit: usize) -> Result<(), PipeErr> {
+        // Data needs to be word aligned.
+        assert!((buf.ptr as u32) & 0x3 == 0);
+        // byte_count section of register is 14 bits.
+        assert!(buf.len < 16_384);
+
+        logln_now!("p{}: Should IN for {}b.", self.num, buf.len);
+        // TODO: should just pass pipe and pregs in, probably.  TODO:
+        // merge with stuff in `send_to_pipe` that also does this.
+        self.desc
+            .bank0
+            .addr
+            .write(|w| unsafe { w.addr().bits(buf.ptr as u32) });
+        self.desc.bank0.pcksize.write(|w| {
+            // FIXME: see note in `send`.
+            unsafe { w.bits(buf.len as u32) }
+            //unsafe { w.byte_count().bits(buf.len as u8) };
+            //unsafe { w.multi_packet_size().bits(0) }
+        });
+
+        // Possibly set PSTATUS.DTGL? Not sure how this works
+        // yet. Arduino would set it here if dispatchPkt returned USB_ERROR_DATATOGGLE
+        //pregs.statusset.write(|w| w.dtgl().set_bit());
+        //pregs.statusclr.write(|w| unsafe {
+        // No function for this. FIXME: need to patch the SVD for
+        // PSTATUSCLR.DTGL at bit0
+        // w.bits(1)
+        //});
+
+        self.dispatch_retries(USBToken::In, nak_limit)
+    }
+
+    pub(crate) fn dispatch_retries(
+        &mut self,
+        token: USBToken,
+        retries: usize,
+    ) -> Result<(), PipeErr> {
+        assert!(retries > 0);
+
+        logln_now!("initial regs");
+        self.log_regs();
+
+        let until = rtc::millis() + USB_TIMEOUT;
+        let mut last_result: Result<(), PipeErr> = Err(PipeErr::SWTimeout);
+        let mut naks = 0;
+        while naks <= retries {
+            logln_now!("p{}: dispatch {:?} retry {}", self.num, token, naks);
+
+            self.dispatch_packet(token);
+            last_result = self.dispatch_result(token, until);
+            match last_result {
+                Ok(_) => return Ok(()),
+                // FIXME: handle datatoggle
+                Err(PipeErr::DataToggle) => {
+                    if self.regs.status.read().dtgl().bit_is_set() {
+                        self.regs.statusset.write(|w| w.dtgl().set_bit());
+                    } else {
+                        self.regs.statusclr.write(|w| unsafe {
+                            // No function for this. FIXME: need to patch the SVD for PSTATUSCLR.DTGL at bit0
+                            w.bits(1)
+                        });
+                    }
+                }
+                Err(PipeErr::SWTimeout) => break,
+                Err(PipeErr::Stall) => break,
+                Err(_) => naks += 1,
+            }
+        }
+
+        last_result
+    }
+
+    fn log_regs(&self) {
+        // Pipe regs
+        let cfg = self.regs.cfg.read().bits();
+        let bin = self.regs.binterval.read().bits();
+        let sts = self.regs.status.read().bits();
+        let ifl = self.regs.intflag.read().bits();
+        logln_now!(
+            "p{}: cfg: {:x}, bin: {:x}, sts: {:x}, ifl: {:x}",
+            self.num,
+            cfg,
+            bin,
+            sts,
+            ifl
+        );
+
+        // Pipe RAM regs
+        let adr = self.desc.bank0.addr.read().bits();
+        let pks = self.desc.bank0.pcksize.read().bits();
+        let ext = self.desc.bank0.extreg.read().bits();
+        let sbk = self.desc.bank0.status_bk.read().bits();
+        let hcp = self.desc.bank0.ctrl_pipe.read().bits();
+        let spi = self.desc.bank0.status_pipe.read().bits();
+        logln_now!(
+            "p{}: adr: {:x}, pks: {:x}, ext: {:x}, sbk: {:x}, hcp: {:x}, spi: {:x}",
+            self.num,
+            adr,
+            pks,
+            ext,
+            sbk,
+            hcp,
+            spi
+        );
+    }
+
+    fn dispatch_packet(&mut self, token: USBToken) {
+        self.regs
+            .cfg
+            .modify(|_, w| unsafe { w.ptoken().bits(token as u8) });
+        match token {
+            USBToken::Setup => {
+                self.regs.intflag.write(|w| w.txstp().set_bit());
+                self.regs.statusset.write(|w| w.bk0rdy().set_bit());
+            }
+            USBToken::In => self.regs.statusclr.write(|w| w.bk0rdy().set_bit()),
+            USBToken::Out => {
+                self.regs.intflag.write(|w| w.trcpt0().set_bit());
+                self.regs.statusset.write(|w| w.bk0rdy().set_bit());
+            }
+            _ => {}
+        }
+        self.regs.statusclr.write(|w| w.pfreeze().set_bit());
+    }
+
+    fn dispatch_result(&mut self, token: USBToken, until: usize) -> Result<(), PipeErr> {
+        while rtc::millis() <= until {
+            if self.is_transfer_complete(token)? {
+                return Ok(());
+            } else if self.regs.intflag.read().stall().bit_is_set() {
+                logln_now!("stall");
+                self.log_regs();
+                self.regs.intflag.write(|w| w.stall().set_bit());
+                return Err(PipeErr::Stall);
+            } else if self.regs.intflag.read().trfail().bit_is_set() {
+                logln_now!("trfail");
+                self.log_regs();
+                self.regs.intflag.write(|w| w.trfail().set_bit());
+                return Err(PipeErr::TransferFail);
+            } else if self.desc.bank0.status_bk.read().errorflow().bit_is_set() {
+                logln_now!("errorflow");
+                self.log_regs();
+                self.desc
+                    .bank0
+                    .status_bk
+                    .write(|w| w.errorflow().clear_bit());
+                return Err(PipeErr::Flow);
+            } else if self.desc.bank0.status_pipe.read().touter().bit_is_set() {
+                logln_now!("touter");
+                self.log_regs();
+                self.desc
+                    .bank0
+                    .status_pipe
+                    .write(|w| w.touter().clear_bit());
+                return Err(PipeErr::HWTimeout);
+            } else if self.desc.bank0.status_pipe.read().dtgler().bit_is_set() {
+                logln_now!("dtgler");
+                self.log_regs();
+                self.desc
+                    .bank0
+                    .status_pipe
+                    .write(|w| w.dtgler().clear_bit());
+                return Err(PipeErr::DataToggle);
+            }
+        }
+        logln_now!("swtimeout");
+        self.log_regs();
+        Err(PipeErr::SWTimeout)
+    }
+
+    fn is_transfer_complete(&mut self, token: USBToken) -> Result<bool, PipeErr> {
+        match token {
+            USBToken::Setup => {
+                if self.regs.intflag.read().txstp().bit_is_set() {
+                    self.regs.intflag.write(|w| w.txstp().set_bit());
+                    self.regs.statusset.write(|w| w.pfreeze().set_bit());
+                    Ok(true)
+                } else {
+                    Ok(false)
+                }
+            }
+            USBToken::In => {
+                if self.regs.intflag.read().trcpt0().bit_is_set() {
+                    self.regs.intflag.write(|w| w.trcpt0().set_bit());
+                    self.regs.statusset.write(|w| w.pfreeze().set_bit());
+                    Ok(true)
+                } else {
+                    Ok(false)
+                }
+            }
+            USBToken::Out => {
+                if self.regs.intflag.read().trcpt0().bit_is_set() {
+                    self.regs.intflag.write(|w| w.trcpt0().set_bit());
+                    self.regs.statusset.write(|w| w.pfreeze().set_bit());
+                    Ok(true)
+                } else {
+                    Ok(false)
+                }
+            }
+            _ => Err(PipeErr::InvalidToken),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub(crate) enum USBToken {
+    Setup = 0,
+    In = 1,
+    Out = 2,
+    Reserved = 3,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub(crate) enum USBPipeType {
+    Disabled = 0x0,
+    Control = 0x1,
+    ISO = 0x2,
+    Bulk = 0x3,
+    Interrupt = 0x4,
+    Extended = 0x5,
+    _Reserved0 = 0x06,
+    _Reserved1 = 0x07,
+}
+
+pub(crate) struct DataBuf<'a> {
+    pub(crate) ptr: *const u8,
+    pub(crate) len: usize,
+    _marker: core::marker::PhantomData<&'a ()>,
+}
+impl DataBuf<'_> {}
+
+impl core::fmt::Debug for DataBuf<'_> {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        write!(f, "DataBuf {{ len: {}, ptr: [", self.len)?;
+        for i in 0..self.len {
+            write!(f, " {:x}", unsafe {
+                *self.ptr.offset(i.try_into().unwrap())
+            })?;
+        }
+        write!(f, " ] }}")
+    }
+}
+
+impl<'a, T> From<&'a T> for DataBuf<'a> {
+    fn from(v: &'a T) -> Self {
+        Self {
+            ptr: v as *const T as *const u8,
+            len: core::mem::size_of::<T>(),
+            _marker: core::marker::PhantomData,
+        }
+    }
+}
+
+pub(crate) struct PipeRegs<'a> {
+    pub(crate) cfg: &'a mut PCFG,
+    pub(crate) binterval: &'a mut BINTERVAL,
+    pub(crate) statusclr: &'a mut PSTATUSCLR,
+    pub(crate) statusset: &'a mut PSTATUSSET,
+    pub(crate) status: &'a mut PSTATUS,
+    pub(crate) intflag: &'a mut PINTFLAG,
+}
+impl<'a> PipeRegs<'a> {
+    pub(crate) fn from(host: &'a mut usb::HOST, i: usize) -> PipeRegs {
+        assert!(i < MAX_PIPES);
+        match i {
+            0 => Self {
+                cfg: &mut host.pcfg0,
+                binterval: &mut host.binterval0,
+                statusclr: &mut host.pstatusclr0,
+                statusset: &mut host.pstatusset0,
+                status: &mut host.pstatus0,
+                intflag: &mut host.pintflag0,
+            },
+            1 => Self {
+                cfg: &mut host.pcfg1,
+                binterval: &mut host.binterval1,
+                statusclr: &mut host.pstatusclr1,
+                statusset: &mut host.pstatusset1,
+                status: &mut host.pstatus1,
+                intflag: &mut host.pintflag1,
+            },
+            2 => Self {
+                cfg: &mut host.pcfg2,
+                binterval: &mut host.binterval2,
+                statusclr: &mut host.pstatusclr2,
+                statusset: &mut host.pstatusset2,
+                status: &mut host.pstatus2,
+                intflag: &mut host.pintflag2,
+            },
+            3 => Self {
+                cfg: &mut host.pcfg3,
+                binterval: &mut host.binterval3,
+                statusclr: &mut host.pstatusclr3,
+                statusset: &mut host.pstatusset3,
+                status: &mut host.pstatus3,
+                intflag: &mut host.pintflag3,
+            },
+            4 => Self {
+                cfg: &mut host.pcfg4,
+                binterval: &mut host.binterval4,
+                statusclr: &mut host.pstatusclr4,
+                statusset: &mut host.pstatusset4,
+                status: &mut host.pstatus4,
+                intflag: &mut host.pintflag4,
+            },
+            5 => Self {
+                cfg: &mut host.pcfg5,
+                binterval: &mut host.binterval5,
+                statusclr: &mut host.pstatusclr5,
+                statusset: &mut host.pstatusset5,
+                status: &mut host.pstatus5,
+                intflag: &mut host.pintflag5,
+            },
+            6 => Self {
+                cfg: &mut host.pcfg6,
+                binterval: &mut host.binterval6,
+                statusclr: &mut host.pstatusclr6,
+                statusset: &mut host.pstatusset6,
+                status: &mut host.pstatus6,
+                intflag: &mut host.pintflag6,
+            },
+            7 => Self {
+                cfg: &mut host.pcfg7,
+                binterval: &mut host.binterval7,
+                statusclr: &mut host.pstatusclr7,
+                statusset: &mut host.pstatusset7,
+                status: &mut host.pstatus7,
+                intflag: &mut host.pintflag7,
+            },
+            _ => unreachable!(),
+        }
+    }
+}
+
+// §32.8.7.1
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct PipeDesc {
+    pub bank0: BankDesc,
+    pub bank1: BankDesc,
+}
+
+// 2 banks: 32 bytes per pipe.
+impl PipeDesc {
+    pub fn new() -> Self {
+        Self {
+            bank0: BankDesc::new(),
+            bank1: BankDesc::new(),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+#[repr(C, packed)]
+// 16 bytes per bank.
+pub(crate) struct BankDesc {
+    pub addr: Addr,
+    pub pcksize: PckSize,
+    pub extreg: ExtReg,
+    pub status_bk: StatusBk,
+    pub ctrl_pipe: CtrlPipe,
+    pub status_pipe: StatusPipe,
+
+    _reserved: u8,
+}
+
+impl BankDesc {
+    fn new() -> Self {
+        Self {
+            addr: Addr::from(0),
+            pcksize: PckSize::from(0),
+            extreg: ExtReg::from(0),
+            status_bk: StatusBk::from(0),
+            ctrl_pipe: CtrlPipe::from(0),
+            status_pipe: StatusPipe::from(0),
+            _reserved: 0,
+        }
+    }
+}
diff --git a/app/src/usb/pipe/addr.rs b/app/src/usb/pipe/addr.rs
new file mode 100644
index 0000000..8b92177
--- /dev/null
+++ b/app/src/usb/pipe/addr.rs
@@ -0,0 +1,87 @@
+/// § 32.8.7.2
+/// Address of the Data Buffer.
+///
+/// Offset: 0x00 & 0x10
+/// Reset: 0xxxxxxxxx
+/// Property: NA
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct Addr(u32);
+
+pub(crate) struct R {
+    bits: u32,
+}
+
+pub(crate) struct W {
+    bits: u32,
+}
+
+impl Addr {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        // Address must be 32-bit aligned.
+        assert!((w.bits & 0x3) == 0);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u32> for Addr {
+    fn from(v: u32) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u32 {
+        self.bits
+    }
+
+    pub fn addr(&self) -> AddrR {
+        AddrR(self.bits)
+    }
+}
+
+/// Data Pointer Address Value
+///
+/// These bits define the data pointer address as an absolute double
+/// word address in RAM. The two least significant bits must be zero
+/// to ensure the descriptor is 32-bit aligned.
+pub(crate) struct AddrR(u32);
+impl AddrR {
+    pub fn bits(&self) -> u32 {
+        self.0
+    }
+}
+
+impl W {
+    /// Write raw bits.
+    pub unsafe fn bits(&mut self, v: u32) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn addr(&mut self) -> AddrW {
+        AddrW { w: self }
+    }
+}
+
+pub(crate) struct AddrW<'a> {
+    w: &'a mut W,
+}
+impl<'a> AddrW<'a> {
+    pub unsafe fn bits(self, v: u32) -> &'a mut W {
+        self.w.bits = v;
+        self.w
+    }
+
+    // TODO: "safe" method take a pointer instead of raw u32
+}
diff --git a/app/src/usb/pipe/ctrl_pipe.rs b/app/src/usb/pipe/ctrl_pipe.rs
new file mode 100644
index 0000000..63390df
--- /dev/null
+++ b/app/src/usb/pipe/ctrl_pipe.rs
@@ -0,0 +1,177 @@
+/// Host Control Pipe.
+///
+/// Offset: 0x0c
+/// Reset: 0xXXXX
+/// Property: PAC Write-Protection, Write-Synchronized, Read-Synchronized
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct CtrlPipe(u16);
+
+pub(crate) struct R {
+    bits: u16,
+}
+
+pub(crate) struct W {
+    bits: u16,
+}
+
+impl CtrlPipe {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u16> for CtrlPipe {
+    fn from(v: u16) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u16 {
+        self.bits
+    }
+
+    pub fn permax(&self) -> PErMaxR {
+        let bits = {
+            const POS: u8 = 12;
+            const MASK: u16 = 0xf;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        PErMaxR(bits)
+    }
+
+    pub fn pepnum(&self) -> PEpNumR {
+        let bits = {
+            const POS: u8 = 8;
+            const MASK: u16 = 0xf;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        PEpNumR(bits)
+    }
+
+    pub fn pdaddr(&self) -> PDAddrR {
+        let bits = {
+            const POS: u8 = 0;
+            const MASK: u16 = 0x3f;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        PDAddrR(bits)
+    }
+}
+
+/// Pipe Error Max Number
+///
+/// These bits define the maximum number of error for this Pipe before
+/// freezing the pipe automatically.
+pub(crate) struct PErMaxR(u8);
+impl PErMaxR {
+    pub fn max(&self) -> u8 {
+        self.0
+    }
+}
+
+/// Pipe EndPoint Number
+///
+/// These bits define the number of endpoint for this Pipe.
+pub(crate) struct PEpNumR(u8);
+impl PEpNumR {
+    pub fn epnum(&self) -> u8 {
+        self.0
+    }
+}
+
+/// Pipe Device Address
+///
+/// These bits define the Device Address for this pipe.
+pub(crate) struct PDAddrR(u8);
+impl PDAddrR {
+    pub fn addr(&self) -> u8 {
+        self.0
+    }
+}
+
+impl W {
+    /// Write raw bits.
+
+    pub unsafe fn bits(&mut self, v: u16) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn permax(&mut self) -> PErMaxW {
+        PErMaxW { w: self }
+    }
+
+    pub fn pepnum(&mut self) -> PEpNumW {
+        PEpNumW { w: self }
+    }
+
+    pub fn pdaddr(&mut self) -> PDAddrW {
+        PDAddrW { w: self }
+    }
+}
+
+pub(crate) struct PErMaxW<'a> {
+    w: &'a mut W,
+}
+impl<'a> PErMaxW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 12;
+        const MASK: u8 = 0xf;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_max(self, v: u8) -> &'a mut W {
+        unsafe { self.bits(v) }
+    }
+}
+
+pub(crate) struct PEpNumW<'a> {
+    w: &'a mut W,
+}
+impl<'a> PEpNumW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 8;
+        const MASK: u8 = 0xf;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_epnum(self, v: u8) -> &'a mut W {
+        unsafe { self.bits(v) }
+    }
+}
+
+pub(crate) struct PDAddrW<'a> {
+    w: &'a mut W,
+}
+impl<'a> PDAddrW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 0;
+        const MASK: u8 = 0x3f;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_addr(self, v: u8) -> &'a mut W {
+        unsafe { self.bits(v) }
+    }
+}
diff --git a/app/src/usb/pipe/ext_reg.rs b/app/src/usb/pipe/ext_reg.rs
new file mode 100644
index 0000000..023ce9f
--- /dev/null
+++ b/app/src/usb/pipe/ext_reg.rs
@@ -0,0 +1,156 @@
+/// §32.8.7.4
+/// Extended Register.
+///
+/// Offset: 0x08
+/// Reset: 0xxxxxxxx
+/// Property: NA
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct ExtReg(u16);
+
+pub(crate) struct R {
+    bits: u16,
+}
+
+pub(crate) struct W {
+    bits: u16,
+}
+
+impl ExtReg {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u16> for ExtReg {
+    fn from(v: u16) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u16 {
+        self.bits
+    }
+
+    pub fn variable(&self) -> VariableR {
+        let bits = {
+            const POS: u8 = 4;
+            const MASK: u16 = 0x7ff;
+            (self.bits >> POS) & MASK
+        };
+
+        VariableR(bits)
+    }
+
+    pub fn subpid(&self) -> SubPIDR {
+        let bits = {
+            const POS: u8 = 0;
+            const MASK: u16 = 0xf;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        SubPIDR(bits)
+    }
+}
+
+/// Variable field send with extended token
+///
+/// These bits define the VARIABLE field sent with extended token. See
+/// “Section 2.1.1 Protocol Extension Token in the reference document
+/// ENGINEERING CHANGE NOTICE, USB 2.0 Link Power Management
+/// Addendum.”
+///
+/// To support the USB2.0 Link Power Management addition the VARIABLE
+/// field should be set as described below.
+///
+/// | VARIABLE       | Description           |
+/// +----------------+-----------------------+
+/// | VARIABLE[3:0]  | bLinkState[1]         |
+/// | VARIABLE[7:4]  | BESL (See LPM ECN)[2] |
+/// | VARIABLE[8]    | bRemoteWake[1]        |
+/// | VARIABLE[10:9] | Reserved              |
+///
+/// [1] for a definition of LPM Token bRemoteWake and bLinkState
+/// fields, refer to "Table 2-3 in the reference document ENGINEERING
+/// CHANGE NOTICE, USB 2.0 Link Power Management Addendum"
+///
+/// [2] for a definition of LPM Token BESL field, refer to "Table 2-3
+/// in the reference document ENGINEERING CHANGE NOTICE, USB 2.0 Link
+/// Power Management Addendum" and "Table X-X1 in Errata for ECN USB
+/// 2.0 Link Power Management.
+pub(crate) struct VariableR(u16);
+impl VariableR {
+    pub fn bits(&self) -> u16 {
+        self.0
+    }
+}
+
+/// SUBPID field with extended token
+///
+/// These bits define the SUBPID field sent with extended token. See
+/// “Section 2.1.1 Protocol Extension Token in the reference document
+/// ENGINEERING CHANGE NOTICE, USB 2.0 Link Power Management
+/// Addendum”.
+///
+/// To support the USB2.0 Link Power Management addition the SUBPID
+/// field should be set as described in “Table 2.2 SubPID Types in the
+/// reference document ENGINEERING CHANGE NOTICE, USB 2.0 Link Power
+/// Management Addendum”.
+pub(crate) struct SubPIDR(u8);
+impl SubPIDR {
+    pub fn bits(&self) -> u8 {
+        self.0
+    }
+}
+
+impl W {
+    /// Write raw bits.
+    pub unsafe fn bits(&mut self, v: u16) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn variable(&mut self) -> VariableW {
+        VariableW { w: self }
+    }
+    pub fn subpid(&mut self) -> SubPIDW {
+        SubPIDW { w: self }
+    }
+}
+
+pub(crate) struct VariableW<'a> {
+    w: &'a mut W,
+}
+impl<'a> VariableW<'a> {
+    pub unsafe fn bits(self, v: u16) -> &'a mut W {
+        const POS: u8 = 4;
+        const MASK: u16 = 0x7ff;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+}
+
+pub(crate) struct SubPIDW<'a> {
+    w: &'a mut W,
+}
+impl<'a> SubPIDW<'a> {
+    pub unsafe fn bits(self, v: u16) -> &'a mut W {
+        const POS: u8 = 0;
+        const MASK: u16 = 0xf;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+}
diff --git a/app/src/usb/pipe/pck_size.rs b/app/src/usb/pipe/pck_size.rs
new file mode 100644
index 0000000..5133005
--- /dev/null
+++ b/app/src/usb/pipe/pck_size.rs
@@ -0,0 +1,360 @@
+/// § 32.8.7.3
+/// Packet Size.
+///
+/// Offset: 0x04 & 0x14
+/// Reset: 0xxxxxxxxx
+/// Property: NA
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct PckSize(u32);
+
+pub(crate) struct R {
+    bits: u32,
+}
+
+pub(crate) struct W {
+    bits: u32,
+}
+
+impl PckSize {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u32> for PckSize {
+    fn from(v: u32) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u32 {
+        self.bits
+    }
+
+    pub fn auto_zlp(&self) -> AutoZLPR {
+        let bits = {
+            const POS: u8 = 31;
+            const MASK: u32 = 1;
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        AutoZLPR(bits)
+    }
+
+    pub fn size(&self) -> SizeR {
+        let bits = {
+            const POS: u8 = 28;
+            const MASK: u32 = 0x7;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        SizeR::from(bits)
+    }
+
+    pub fn multi_packet_size(&self) -> MultiPacketSizeR {
+        let bits = {
+            const POS: u8 = 14;
+            const MASK: u32 = 0x3fff;
+            ((self.bits >> POS) & MASK) as u16
+        };
+
+        MultiPacketSizeR(bits)
+    }
+
+    pub fn byte_count(&self) -> ByteCountR {
+        let bits = {
+            const POS: u8 = 8;
+            const MASK: u32 = 0x3f;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        ByteCountR(bits)
+    }
+}
+
+/// Automatic Zero Length Packet
+///
+/// This bit defines the automatic Zero Length Packet mode of the
+/// pipe.
+///
+/// When enabled, the USB module will manage the ZLP handshake by
+/// hardware. This bit is for OUT pipes only. When disabled the
+/// handshake should be managed by firmware.
+pub(crate) struct AutoZLPR(bool);
+impl AutoZLPR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit()
+    }
+}
+
+/// Pipe size
+///
+/// These bits contains the size of the pipe.
+///
+/// These bits are cleared upon sending a USB reset.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(crate) enum SizeR {
+    Bytes8,
+    Bytes16,
+    Bytes32,
+    Bytes64,
+    Bytes128,
+    Bytes256,
+    Bytes512,
+    Bytes1024,
+}
+
+impl SizeR {
+    pub fn bits(&self) -> u8 {
+        match *self {
+            Self::Bytes8 => 0x0,
+            Self::Bytes16 => 0x1,
+            Self::Bytes32 => 0x2,
+            Self::Bytes64 => 0x3,
+            Self::Bytes128 => 0x4,
+            Self::Bytes256 => 0x5,
+            Self::Bytes512 => 0x6,
+            Self::Bytes1024 => 0x7,
+        }
+    }
+
+    fn is_bytes8(&self) -> bool {
+        *self == Self::Bytes8
+    }
+    fn is_bytes16(&self) -> bool {
+        *self == Self::Bytes16
+    }
+    fn is_bytes32(&self) -> bool {
+        *self == Self::Bytes32
+    }
+    fn is_bytes64(&self) -> bool {
+        *self == Self::Bytes64
+    }
+    fn is_bytes128(&self) -> bool {
+        *self == Self::Bytes128
+    }
+    fn is_bytes256(&self) -> bool {
+        *self == Self::Bytes256
+    }
+    fn is_bytes512(&self) -> bool {
+        *self == Self::Bytes512
+    }
+    fn is_bytes1024(&self) -> bool {
+        *self == Self::Bytes1024
+    }
+}
+
+impl From<u8> for SizeR {
+    fn from(v: u8) -> Self {
+        match v {
+            0x0 => Self::Bytes8,
+            0x1 => Self::Bytes16,
+            0x2 => Self::Bytes32,
+            0x3 => Self::Bytes64,
+            0x4 => Self::Bytes128,
+            0x5 => Self::Bytes256,
+            0x6 => Self::Bytes512,
+            0x7 => Self::Bytes1024,
+            _ => panic!("pcksize between 0 and 7 only"),
+        }
+    }
+}
+
+/// Multi Packet IN or OUT size
+///
+/// These bits define the 14-bit value that is used for multi-packet
+/// transfers.
+///
+/// For IN pipes, MULTI_PACKET_SIZE holds the total number of bytes
+/// sent. MULTI_PACKET_SIZE should be written to zero when setting up
+/// a new transfer.
+///
+/// For OUT pipes, MULTI_PACKET_SIZE holds the total data size for the
+/// complete transfer. This value must be a multiple of the maximum
+/// packet size.
+pub(crate) struct MultiPacketSizeR(u16);
+impl MultiPacketSizeR {
+    pub fn bits(&self) -> u16 {
+        self.0
+    }
+}
+
+/// Byte Count
+///
+/// These bits define the 14-bit value that contains number of bytes
+/// sent in the last OUT or SETUP transaction for an OUT pipe, or of
+/// the number of bytes to be received in the next IN transaction for
+/// an input pipe.
+pub(crate) struct ByteCountR(u8);
+impl ByteCountR {
+    pub fn bits(&self) -> u8 {
+        self.0
+    }
+}
+
+impl W {
+    /// Write raw bits.
+    pub unsafe fn bits(&mut self, v: u32) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn auto_zlp(&mut self) -> AutoZLPW {
+        AutoZLPW { w: self }
+    }
+
+    pub fn size(&mut self) -> _SizeW {
+        _SizeW { w: self }
+    }
+
+    pub fn multi_packet_size(&mut self) -> MultiPacketSizeW {
+        MultiPacketSizeW { w: self }
+    }
+
+    pub fn byte_count(&mut self) -> ByteCountW {
+        ByteCountW { w: self }
+    }
+}
+
+pub(crate) struct AutoZLPW<'a> {
+    w: &'a mut W,
+}
+impl<'a> AutoZLPW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 31;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u32) << POS);
+        self.w.bits |= ((v & MASK) as u32) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub(crate) enum SizeW {
+    Bytes8,
+    Bytes16,
+    Bytes32,
+    Bytes64,
+    Bytes128,
+    Bytes256,
+    Bytes512,
+    Bytes1024,
+}
+impl SizeW {
+    pub fn bits(&self) -> u8 {
+        match *self {
+            Self::Bytes8 => 0,
+            Self::Bytes16 => 1,
+            Self::Bytes32 => 2,
+            Self::Bytes64 => 3,
+            Self::Bytes128 => 4,
+            Self::Bytes256 => 5,
+            Self::Bytes512 => 6,
+            Self::Bytes1024 => 7,
+        }
+    }
+}
+
+/// Proxy for `SizeW`
+pub(crate) struct _SizeW<'a> {
+    w: &'a mut W,
+}
+impl<'a> _SizeW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 28;
+        const MASK: u8 = 0x7;
+        self.w.bits &= !((MASK as u32) << POS);
+        self.w.bits |= ((v & MASK) as u32) << POS;
+        self.w
+    }
+
+    pub fn variant(self, v: SizeW) -> &'a mut W {
+        unsafe { self.bits(v.bits()) }
+    }
+
+    pub fn bytes8(self) -> &'a mut W {
+        self.variant(SizeW::Bytes8)
+    }
+
+    pub fn bytes16(self) -> &'a mut W {
+        self.variant(SizeW::Bytes16)
+    }
+
+    pub fn bytes32(self) -> &'a mut W {
+        self.variant(SizeW::Bytes32)
+    }
+
+    pub fn bytes64(self) -> &'a mut W {
+        self.variant(SizeW::Bytes64)
+    }
+
+    pub fn bytes128(self) -> &'a mut W {
+        self.variant(SizeW::Bytes128)
+    }
+
+    pub fn bytes256(self) -> &'a mut W {
+        self.variant(SizeW::Bytes256)
+    }
+
+    pub fn bytes512(self) -> &'a mut W {
+        self.variant(SizeW::Bytes512)
+    }
+
+    pub fn bytes1024(self) -> &'a mut W {
+        self.variant(SizeW::Bytes1024)
+    }
+}
+
+pub(crate) struct MultiPacketSizeW<'a> {
+    w: &'a mut W,
+}
+impl<'a> MultiPacketSizeW<'a> {
+    pub unsafe fn bits(self, v: u16) -> &'a mut W {
+        const POS: u8 = 14;
+        const MASK: u16 = 0x3fff;
+        self.w.bits &= !((MASK as u32) << POS);
+        self.w.bits |= ((v & MASK) as u32) << POS;
+        self.w
+    }
+}
+
+pub(crate) struct ByteCountW<'a> {
+    w: &'a mut W,
+}
+impl<'a> ByteCountW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 8;
+        const MASK: u8 = 0x3f;
+        self.w.bits &= !((MASK as u32) << POS);
+        self.w.bits |= ((v & MASK) as u32) << POS;
+        self.w
+    }
+}
diff --git a/app/src/usb/pipe/status_bk.rs b/app/src/usb/pipe/status_bk.rs
new file mode 100644
index 0000000..4ddb420
--- /dev/null
+++ b/app/src/usb/pipe/status_bk.rs
@@ -0,0 +1,170 @@
+/// §32.8.7.5
+/// Host Status Bank.
+///
+/// Offset: 0x0a & 0x1a
+/// Reset: 0xxxxxxx
+/// Property: NA
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct StatusBk(u8);
+
+pub(crate) struct R {
+    bits: u8,
+}
+
+pub(crate) struct W {
+    bits: u8,
+}
+
+impl StatusBk {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u8> for StatusBk {
+    fn from(v: u8) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u8 {
+        self.bits
+    }
+
+    pub fn errorflow(&self) -> ErrorFlowR {
+        let bits = {
+            const POS: u8 = 1;
+            const MASK: u8 = 1;
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        ErrorFlowR(bits)
+    }
+
+    pub fn crcerr(&self) -> CRCErrR {
+        let bits = {
+            const POS: u8 = 0;
+            const MASK: u8 = 1;
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        CRCErrR(bits)
+    }
+}
+
+/// Error Flow Status
+///
+/// This bit defines the Error Flow Status.
+///
+/// This bit is set when a Error Flow has been detected during
+/// transfer from/towards this bank.
+///
+/// For IN transfer, a NAK handshake has been received. For OUT
+/// transfer, a NAK handshake has been received. For Isochronous IN
+/// transfer, an overrun condition has occurred. For Isochronous OUT
+/// transfer, an underflow condition has occurred.
+pub(crate) struct ErrorFlowR(bool);
+impl ErrorFlowR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+/// CRC Error
+///
+/// This bit defines the CRC Error Status.
+///
+/// This bit is set when a CRC error has been detected in an
+/// isochronous IN endpoint bank.
+pub(crate) struct CRCErrR(bool);
+impl CRCErrR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+impl W {
+    /// Write raw bits.
+    pub unsafe fn bits(&mut self, v: u8) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn errorflow(&mut self) -> ErrorFlowW {
+        ErrorFlowW { w: self }
+    }
+
+    pub fn crcerr(&mut self) -> CRCErrW {
+        CRCErrW { w: self }
+    }
+}
+
+pub(crate) struct ErrorFlowW<'a> {
+    w: &'a mut W,
+}
+impl<'a> ErrorFlowW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 1;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u8) << POS);
+        self.w.bits |= ((v & MASK) as u8) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+pub(crate) struct CRCErrW<'a> {
+    w: &'a mut W,
+}
+impl<'a> CRCErrW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 0;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u8) << POS);
+        self.w.bits |= ((v & MASK) as u8) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
diff --git a/app/src/usb/pipe/status_pipe.rs b/app/src/usb/pipe/status_pipe.rs
new file mode 100644
index 0000000..4f8eb41
--- /dev/null
+++ b/app/src/usb/pipe/status_pipe.rs
@@ -0,0 +1,407 @@
+/// Host Status Pipe.
+///
+/// Offset: 0x0e & 0x1e
+/// Reset: 0xxxxxx
+/// Property: PAC Write-Protection, Write-Synchronized, Read-Synchronized
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub(crate) struct StatusPipe(u16);
+
+pub(crate) struct R {
+    bits: u16,
+}
+pub(crate) struct W {
+    bits: u16,
+}
+
+impl StatusPipe {
+    pub fn read(&self) -> R {
+        R { bits: self.0 }
+    }
+
+    pub fn write<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut W) -> &mut W,
+    {
+        let mut w = W { bits: self.0 };
+        f(&mut w);
+        self.0 = w.bits;
+    }
+}
+
+impl From<u16> for StatusPipe {
+    fn from(v: u16) -> Self {
+        Self(v)
+    }
+}
+
+impl R {
+    /// Value in raw bits.
+    pub fn bits(&self) -> u16 {
+        self.bits
+    }
+
+    pub fn ercnt(&self) -> ErCntR {
+        let bits = {
+            const POS: u8 = 5;
+            const MASK: u16 = 0x7;
+            ((self.bits >> POS) & MASK) as u8
+        };
+
+        ErCntR(bits)
+    }
+
+    pub fn crc16er(&self) -> CRC16ErR {
+        let bits = {
+            const POS: u8 = 4;
+            const MASK: u16 = 1;
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        CRC16ErR(bits)
+    }
+
+    pub fn touter(&self) -> TOutErrR {
+        let bits = {
+            const POS: u8 = 3;
+            const MASK: u16 = 1;
+
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        TOutErrR(bits)
+    }
+
+    pub fn pider(&self) -> PIDErR {
+        let bits = {
+            const POS: u8 = 2;
+            const MASK: u16 = 1;
+
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        PIDErR(bits)
+    }
+
+    pub fn dapider(&self) -> DaPIDErR {
+        let bits = {
+            const POS: u8 = 1;
+            const MASK: u16 = 1;
+
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        DaPIDErR(bits)
+    }
+
+    pub fn dtgler(&self) -> DTglErR {
+        let bits = {
+            const POS: u8 = 0;
+            const MASK: u16 = 1;
+
+            ((self.bits >> POS) & MASK) == 1
+        };
+
+        DTglErR(bits)
+    }
+}
+
+/// Pipe Error Counter
+///
+/// The number of errors detected on the pipe.
+pub(crate) struct ErCntR(u8);
+impl ErCntR {
+    pub fn bits(&self) -> u8 {
+        self.0
+    }
+}
+
+/// CRC16 ERROR
+///
+/// This bit defines the CRC16 Error Status.
+///
+/// This bit is set when a CRC 16 error has been detected during a IN
+/// transactions.
+pub(crate) struct CRC16ErR(bool);
+impl CRC16ErR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+/// TIME OUT ERROR
+///
+/// This bit defines the Time Out Error Status.
+///
+/// This bit is set when a Time Out error has been detected during a
+/// USB transaction.
+pub(crate) struct TOutErrR(bool);
+impl TOutErrR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+/// PID ERROR
+///
+/// This bit defines the PID Error Status.
+///
+/// This bit is set when a PID error has been detected during a USB
+/// transaction.
+pub(crate) struct PIDErR(bool);
+impl PIDErR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+/// Data PID ERROR
+///
+/// This bit defines the PID Error Status.
+///
+/// This bit is set when a Data PID error has been detected during a
+/// USB transaction.
+pub(crate) struct DaPIDErR(bool);
+impl DaPIDErR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+/// Data Toggle Error
+///
+/// This bit defines the Data Toggle Error Status.
+///
+/// This bit is set when a Data Toggle Error has been detected.
+pub(crate) struct DTglErR(bool);
+impl DTglErR {
+    pub fn bit(&self) -> bool {
+        self.0
+    }
+
+    pub fn bit_is_set(&self) -> bool {
+        self.bit()
+    }
+
+    pub fn bit_is_clear(&self) -> bool {
+        !self.bit_is_set()
+    }
+}
+
+impl W {
+    /// Write raw bits.
+    pub unsafe fn bits(&mut self, v: u16) -> &mut Self {
+        self.bits = v;
+        self
+    }
+
+    pub fn ercnt(&mut self) -> ErCntW {
+        ErCntW { w: self }
+    }
+
+    pub fn crc16er(&mut self) -> CRC16ErW {
+        CRC16ErW { w: self }
+    }
+
+    pub fn touter(&mut self) -> TOutErW {
+        TOutErW { w: self }
+    }
+
+    pub fn pider(&mut self) -> PIDErW {
+        PIDErW { w: self }
+    }
+
+    pub fn dapider(&mut self) -> DaPIDErW {
+        DaPIDErW { w: self }
+    }
+
+    pub fn dtgler(&mut self) -> DTglErW {
+        DTglErW { w: self }
+    }
+}
+
+/// Pipe Error Counter
+///
+/// The number of errors detected on the pipe.
+pub(crate) struct ErCntW<'a> {
+    w: &'a mut W,
+}
+impl<'a> ErCntW<'a> {
+    pub unsafe fn bits(self, v: u8) -> &'a mut W {
+        const POS: u8 = 5;
+        const MASK: u8 = 0x7;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_count(self, v: u8) -> &'a mut W {
+        unsafe { self.bits(v) }
+    }
+}
+
+/// CRC16 ERROR
+///
+/// This bit defines the CRC16 Error Status.
+///
+/// This bit is set when a CRC 16 error has been detected during a IN
+/// transactions.
+pub(crate) struct CRC16ErW<'a> {
+    w: &'a mut W,
+}
+impl<'a> CRC16ErW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 4;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+/// TIME OUT ERROR
+///
+/// This bit defines the Time Out Error Status.
+///
+/// This bit is set when a Time Out error has been detected during a
+/// USB transaction.
+pub(crate) struct TOutErW<'a> {
+    w: &'a mut W,
+}
+impl<'a> TOutErW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 3;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+/// PID ERROR
+///
+/// This bit defines the PID Error Status.
+///
+/// This bit is set when a PID error has been detected during a USB
+/// transaction.
+pub(crate) struct PIDErW<'a> {
+    w: &'a mut W,
+}
+impl<'a> PIDErW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 2;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+/// Data PID ERROR
+///
+/// This bit defines the PID Error Status.
+///
+/// This bit is set when a Data PID error has been detected during a
+/// USB transaction.
+pub(crate) struct DaPIDErW<'a> {
+    w: &'a mut W,
+}
+impl<'a> DaPIDErW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 1;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
+
+/// Data Toggle Error
+///
+/// This bit defines the Data Toggle Error Status.
+///
+/// This bit is set when a Data Toggle Error has been detected.
+pub(crate) struct DTglErW<'a> {
+    w: &'a mut W,
+}
+impl<'a> DTglErW<'a> {
+    pub fn bit(self, v: bool) -> &'a mut W {
+        const POS: u8 = 0;
+        const MASK: bool = true;
+        self.w.bits &= !((MASK as u16) << POS);
+        self.w.bits |= ((v & MASK) as u16) << POS;
+        self.w
+    }
+
+    pub fn set_bit(self) -> &'a mut W {
+        self.bit(true)
+    }
+
+    pub fn clear_bit(self) -> &'a mut W {
+        self.bit(false)
+    }
+}
diff --git a/app/src/usb/usbproto.rs b/app/src/usb/usbproto.rs
new file mode 100644
index 0000000..9a86ed7
--- /dev/null
+++ b/app/src/usb/usbproto.rs
@@ -0,0 +1,331 @@
+/// USB Protocol level types and functions.
+///
+/// Everything in here is defined by the USB specification, and
+/// hardware independent.
+
+// TODO: Put protocol section references in for types and
+// documentation.
+
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(C, packed)]
+pub struct USBDeviceDescriptor {
+    pub b_length: u8,
+    pub b_descriptor_type: u8,
+    pub bcd_usb: u16,
+    pub b_device_class: u8,
+    pub b_device_sub_class: u8,
+    pub b_device_protocol: u8,
+    pub b_max_packet_size: u8,
+    pub id_vendor: u16,
+    pub id_product: u16,
+    pub bcd_device: u16,
+    pub i_manufacturer: u8,
+    pub i_product: u8,
+    pub i_serial_number: u8,
+    pub b_num_configurations: u8,
+}
+
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(C, packed)]
+pub struct USBConfigurationDescriptor {
+    pub b_length: u8,
+    pub b_descriptor_type: u8,
+    pub w_total_length: u16,
+    pub b_num_interfaces: u8,
+    pub b_configuration_value: u8,
+    pub i_configuration: u8,
+    pub bm_attributes: u8,
+    pub b_max_power: u8,
+}
+
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(C, packed)]
+pub struct USBInterfaceDescriptor {
+    pub b_length: u8,
+    pub b_descriptor_type: u8,
+    pub b_interface_number: u8,
+    pub b_alternate_setting: u8,
+    pub b_num_endpoints: u8,
+    pub b_interface_class: u8,
+    pub b_interface_sub_class: u8,
+    pub b_interface_protocol: u8,
+    pub i_interface: u8,
+}
+
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(C, packed)]
+pub struct USBEndpointDescriptor {
+    pub b_length: u8,
+    pub b_descriptor_type: u8,
+    pub b_endpoint_address: u8,
+    pub bm_attributes: u8,
+    pub w_max_packet_size: u16,
+    pub b_interval: u8,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[repr(C, packed)]
+pub struct USBSetupPacket {
+    pub bm_request_type: BMRequestType,
+    pub b_request: USBRequest,
+    pub w_value: WValue,
+    pub w_index: u16,
+    pub w_length: u16,
+}
+// TODO: shortcuts for standard device requests §9.4 of USB standard.
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum USBSetupDirection {
+    HostToDevice = 0x00,
+    DeviceToHost = 0x80,
+}
+impl<T> From<T> for USBSetupDirection
+where
+    T: Into<u8>,
+{
+    fn from(v: T) -> Self {
+        match v.into() {
+            0x00 => Self::HostToDevice,
+            0x80 => Self::DeviceToHost,
+            _ => panic!("direction can only be 0x00 or 0x80"),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum USBSetupType {
+    Standard = 0x00,
+    Class = 0x20,
+    Vendor = 0x40,
+}
+impl<T> From<T> for USBSetupType
+where
+    T: Into<u8>,
+{
+    fn from(v: T) -> Self {
+        match v.into() {
+            0x00 => Self::Standard,
+            0x20 => Self::Class,
+            0x40 => Self::Vendor,
+            _ => panic!("type can only be 0x00, 0x20, or 0x40"),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum USBSetupRecipient {
+    Device = 0x00,
+    Interface = 0x01,
+    Endpoint = 0x02,
+    Other = 0x03,
+}
+impl<T> From<T> for USBSetupRecipient
+where
+    T: Into<u8>,
+{
+    fn from(v: T) -> Self {
+        match v.into() {
+            0x00 => Self::Device,
+            0x01 => Self::Interface,
+            0x02 => Self::Endpoint,
+            0x03 => Self::Other,
+            _ => panic!("recipient can only be between 0 and 3"),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+#[repr(C)]
+pub struct BMRequestType(u8);
+impl BMRequestType {
+    // Get descriptor request type.
+    pub fn get_descr() -> Self {
+        Self::from((
+            USBSetupDirection::DeviceToHost,
+            USBSetupType::Standard,
+            USBSetupRecipient::Device,
+        ))
+    }
+
+    // Set request type for all but 'set feature' and 'set interface'.
+    pub fn set() -> Self {
+        Self::from((
+            USBSetupDirection::HostToDevice,
+            USBSetupType::Standard,
+            USBSetupRecipient::Device,
+        ))
+    }
+
+    // Get interface request type.
+    pub fn cl_get_intf() -> Self {
+        Self::from((
+            USBSetupDirection::DeviceToHost,
+            USBSetupType::Class,
+            USBSetupRecipient::Interface,
+        ))
+    }
+
+    pub fn recipient(&self) -> USBSetupRecipient {
+        const POS: u8 = 0;
+        const MASK: u8 = 0x1f;
+        (self.0 & (MASK << POS)).into()
+    }
+
+    pub fn set_recipient(&mut self, v: USBSetupRecipient) {
+        const POS: u8 = 0;
+        const MASK: u8 = 0x1f;
+        self.0 &= !(MASK << POS);
+        self.0 |= v as u8 & MASK;
+    }
+
+    pub fn typ(&self) -> USBSetupType {
+        const POS: u8 = 5;
+        const MASK: u8 = 0x3;
+        (self.0 & (MASK << POS)).into()
+    }
+
+    pub fn set_typ(&mut self, v: USBSetupType) {
+        const POS: u8 = 5;
+        const MASK: u8 = 0x3;
+        self.0 &= !(MASK << POS);
+        self.0 |= v as u8 & MASK;
+    }
+
+    pub fn direction(&self) -> USBSetupDirection {
+        const POS: u8 = 7;
+        const MASK: u8 = 0x1;
+        (self.0 & (MASK << POS)).into()
+    }
+
+    pub fn set_direction(&mut self, v: USBSetupDirection) {
+        const POS: u8 = 7;
+        const MASK: u8 = 0x1;
+        self.0 &= !(MASK << POS);
+        self.0 |= v as u8 & MASK;
+    }
+}
+impl From<u8> for BMRequestType {
+    fn from(v: u8) -> Self {
+        Self(v)
+    }
+}
+impl From<(USBSetupDirection, USBSetupType, USBSetupRecipient)> for BMRequestType {
+    fn from(v: (USBSetupDirection, USBSetupType, USBSetupRecipient)) -> Self {
+        Self(v.0 as u8 | v.1 as u8 | v.2 as u8)
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+#[repr(C)]
+pub struct WValue(u16);
+impl WValue {
+    pub fn w_value_lo(&self) -> u8 {
+        const POS: u8 = 0;
+        const MASK: u16 = 0xff;
+        ((self.0 >> POS) & MASK) as u8
+    }
+
+    pub fn set_w_value_lo(&mut self, v: u8) {
+        const POS: u8 = 0;
+        const MASK: u8 = 0xff;
+        self.0 &= !((MASK as u16) << POS);
+        self.0 |= ((v & MASK) as u16) << POS;
+    }
+
+    pub fn w_value_hi(&self) -> u8 {
+        const POS: u8 = 8;
+        const MASK: u16 = 0xff;
+        ((self.0 >> POS) & MASK) as u8
+    }
+
+    pub fn set_w_value_hi(&mut self, v: u8) {
+        const POS: u8 = 8;
+        const MASK: u8 = 0xff;
+        self.0 &= !((MASK as u16) << POS);
+        self.0 |= ((v & MASK) as u16) << POS;
+    }
+}
+impl From<(u8, u8)> for WValue {
+    fn from(v: (u8, u8)) -> Self {
+        let mut rc = Self(0);
+        rc.set_w_value_lo(v.0);
+        rc.set_w_value_hi(v.1);
+        rc
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum USBRequest {
+    GetStatus = 0,
+    ClearFeature = 1,
+    SetFeature = 3,
+    SetAddress = 5,
+    GetDescriptor = 6,
+    SetDescriptor = 7,
+    GetConfiguration = 8,
+    SetConfiguration = 9,
+    GetInterface = 10,
+    SetInterface = 11,
+    SynchFrame = 12,
+}
+impl<T> From<T> for USBRequest
+where
+    T: Into<u8>,
+{
+    fn from(v: T) -> Self {
+        match v.into() {
+            0 => Self::GetStatus,
+            1 => Self::ClearFeature,
+            3 => Self::SetFeature,
+            5 => Self::SetAddress,
+            6 => Self::GetDescriptor,
+            7 => Self::SetDescriptor,
+            8 => Self::GetConfiguration,
+            9 => Self::SetConfiguration,
+            10 => Self::GetInterface,
+            11 => Self::SetInterface,
+            12 => Self::SynchFrame,
+            _ => panic!("invalid request value"),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum USBFeature {
+    EndpointHalt = 0,
+    DeviceRemoteWakeup = 1,
+    TestMode = 2,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum USBDescriptor {
+    Device = 0x01,
+    Configuration = 0x02,
+    String = 0x03,
+    Interface = 0x04,
+    Endpoint = 0x05,
+    DeviceQualifier = 0x06,
+    OtherSpeed = 0x07,
+    InterfacePower = 0x08,
+    OTG = 0x09,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum HIDDescriptor {
+    HID = 0x21,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum OTGFeature {
+    BHNPEnable = 3,
+    AHNPSupport = 4,
+    AAltHNPSupport = 5,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum USBTransferType {
+    Control = 0x00,
+    Isochronous = 0x01,
+    Bulk = 0x02,
+    Interrupt = 0x03,
+}
diff --git a/rb/Cargo.lock b/rb/Cargo.lock
new file mode 100644
index 0000000..1adf307
--- /dev/null
+++ b/rb/Cargo.lock
@@ -0,0 +1,6 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "rb"
+version = "0.1.0"
+
diff --git a/rb/Cargo.toml b/rb/Cargo.toml
new file mode 100644
index 0000000..d18a9e2
--- /dev/null
+++ b/rb/Cargo.toml
@@ -0,0 +1,5 @@
+[package]
+name = "rb"
+version = "0.1.0"
+authors = ["Brian Cully <bjc@kublai.com>"]
+edition = "2018"
diff --git a/rb/src/lib.rs b/rb/src/lib.rs
new file mode 100755
index 0000000..d51bb26
--- /dev/null
+++ b/rb/src/lib.rs
@@ -0,0 +1,221 @@
+// FIXME: Currently RingBuffer requires its type parameter to be
+// `Copy` because items are stored in a fixed-length array (which,
+// itself, is required to allow creating RingBuffers
+// statically). There may be work-arounds with ptr routines, and it
+// should be investigated.
+//
+// TODO: Needs impls for Iter/IterMut.
+#![no_std]
+#![feature(const_fn)]
+
+use core::{
+    cell::UnsafeCell,
+    marker::PhantomData,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+
+/// Underlying buffer capacity. Needs to be hard-coded for now,
+/// because the size of the structure needs to be known at compile
+/// time so it can be statically allocated or created on the stack.
+///
+/// This will disappear when const generics appear.
+const CAPACITY: usize = 256;
+
+#[derive(Debug, PartialEq)]
+pub enum Error {
+    BufferFull,
+}
+
+/// A lock-free concurrent ring buffer that prevents overwriting data
+/// before it is read.
+pub struct RingBuffer<T> {
+    head: AtomicUsize,
+    tail: AtomicUsize,
+
+    // Backing store needs to be UnsafeCell to make sure it's not
+    // stored in read-only data sections.
+    buf: UnsafeCell<[T; CAPACITY]>,
+}
+
+impl<T> RingBuffer<T>
+where
+    T: Copy,
+{
+    /// Create a new RingBuffer.
+    pub const fn new(default: T) -> Self {
+        Self {
+            head: AtomicUsize::new(0),
+            tail: AtomicUsize::new(0),
+            buf: UnsafeCell::new([default; CAPACITY]),
+        }
+    }
+
+    // Honestly, this should consume `self` or at least be `mut`, but
+    // it needs to be available in const static contexts, which
+    // prevents that. Basically all the rest of the unsafe stuff in
+    // here is a consequence of that.
+    //
+    // No, lazy_static is not an option, because it doesn't work on
+    // architectures where CAS atomics are missing.
+    pub const fn split<'a>(&'a self) -> (Reader<T>, Writer<T>) {
+        let rbr = Reader {
+            rb: self as *const _,
+            _marker: PhantomData,
+        };
+        let rbw = Writer {
+            rb: self as *const _,
+            _marker: PhantomData,
+        };
+        (rbr, rbw)
+    }
+}
+
+pub struct Reader<'a, T> {
+    rb: *const RingBuffer<T>,
+    _marker: PhantomData<&'a ()>,
+}
+unsafe impl<T> Send for Reader<'_, T> where T: Send {}
+unsafe impl<T> Sync for Reader<'_, T> {}
+
+pub struct Writer<'a, T> {
+    rb: *const RingBuffer<T>,
+    _marker: PhantomData<&'a ()>,
+}
+unsafe impl<T> Send for Writer<'_, T> where T: Send {}
+unsafe impl<T> Sync for Writer<'_, T> {}
+
+impl<'a, T> Reader<'a, T>
+where
+    T: Copy,
+{
+    pub fn len(&self) -> usize {
+        let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
+        let h = rb.head.load(Ordering::SeqCst);
+        let t = rb.tail.load(Ordering::SeqCst);
+        let rc = (t + CAPACITY - h) % CAPACITY;
+        rc
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Returns the value at the start of the buffer and advances the
+    /// start of the buffer to the next element.
+    ///
+    /// If nothing is available in the buffer, returns `None`
+    pub fn shift(&mut self) -> Option<T> {
+        let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
+        let h = rb.head.load(Ordering::SeqCst);
+        let t = rb.tail.load(Ordering::SeqCst);
+        if h == t {
+            None
+        } else {
+            let nh = (h + 1) % CAPACITY;
+            let buf = unsafe { &mut *rb.buf.get() };
+            let rc = Some(buf[h]);
+            rb.head.store(nh, Ordering::SeqCst);
+            rc
+        }
+    }
+}
+
+impl<'a, T> Writer<'a, T>
+where
+    T: Copy,
+{
+    /// Put `v` at the end of the buffer.
+    ///
+    /// Returns `BufferFull` if appending `v` would overlap with the
+    /// start of the buffer.
+    pub fn unshift(&mut self, v: T) -> Result<(), Error> {
+        let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
+        let h = rb.head.load(Ordering::SeqCst);
+        let t = rb.tail.load(Ordering::SeqCst);
+        let nt = (t + 1) % CAPACITY;
+        // We can't allow overwrites of the head position, because it
+        // would then be possible to write to the same memory location
+        // that is being read. If reading a value of `T` takes more
+        // than one memory read, then reading from the head would
+        // produce garbage in this scenario.
+        if nt == h {
+            // FIXME: this comparison is wrong in the trivial
+            // 1-element buffer case which would never allow an
+            // `unshift`. In larger buffers it wastes a buffer slot.
+            Err(Error::BufferFull)
+        } else {
+            let buf = unsafe { &mut *rb.buf.get() };
+            buf[t] = v;
+            rb.tail.store(nt, Ordering::SeqCst);
+            Ok(())
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn detects_empty() {
+        let rb = RingBuffer::<bool>::new(false);
+        let (mut rbr, mut rbw) = rb.split();
+        assert!(rbr.is_empty());
+        rbw.unshift(true).ok();
+        assert!(!rbr.is_empty());
+        rbr.shift();
+        assert!(rbr.is_empty());
+    }
+
+    #[test]
+    fn len_matches() {
+        let rb = RingBuffer::<bool>::new(false);
+        let (mut rbr, mut rbw) = rb.split();
+
+        // Count length up.
+        for i in 0..CAPACITY - 1 {
+            assert_eq!(rbr.len(), i);
+            assert_eq!(rbw.unshift(true), Ok(()));
+        }
+
+        // ...and back down again.
+        for i in 0..CAPACITY - 1 {
+            assert_eq!(rbr.len(), CAPACITY - 1 - i);
+            rbr.shift();
+        }
+
+        // Final check for empty.
+        assert_eq!(rbr.len(), 0);
+    }
+
+    #[test]
+    fn can_wrap() {
+        let rb = RingBuffer::<usize>::new(0);
+        let (mut rbr, mut rbw) = rb.split();
+
+        // Make sure we can store n-1 elements.
+        for i in 0..CAPACITY - 1 {
+            assert_eq!(rbw.unshift(i), Ok(()))
+        }
+
+        // ...and that we can load them back again.
+        for i in 0..CAPACITY - 1 {
+            assert_eq!(rbr.shift(), Some(i))
+        }
+    }
+
+    #[test]
+    fn cannot_overwrite() {
+        let rb = RingBuffer::<usize>::new(0);
+        let (mut rbr, mut rbw) = rb.split();
+
+        for i in 0..CAPACITY - 1 {
+            assert_eq!(rbw.unshift(i), Ok(()));
+        }
+        assert_eq!(rbw.unshift(0xffff), Err(Error::BufferFull));
+
+        // We can drop an element to allow a slot to write to again.
+        rbr.shift();
+        assert_eq!(rbw.unshift(0xffff), Ok(()));
+    }
+}