1 files changed, 139 insertions, 0 deletions
diff --git a/samd21-host/examples/simple/logger.rs b/samd21-host/examples/simple/logger.rs
new file mode 100644
index 0000000..9f9452e
--- /dev/null
+++ b/samd21-host/examples/simple/logger.rs
@@ -0,0 +1,139 @@
+use crate::rtc;
+use rb::{Reader, RingBuffer, Writer};
+
+use core::cell::UnsafeCell;
+use core::fmt::{self, Write};
+use embedded_hal::{digital::v2::OutputPin, serial};
+use log::{Metadata, Record};
+use trinket_m0::{
+    gpio::{Pa6, Pa7, PfD},
+    sercom::{Sercom0Pad2, Sercom0Pad3, UART0},
+};
+
+static mut UART0: usize = 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 fmt::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 LB: RingBuffer<u8> = RingBuffer::<u8>::new(0);
+static mut JRB: JoinedRingBuffer = unsafe { JoinedRingBuffer::new(&LB) };
+
+// The UART isn't necessarily Sync, so wrap it in something that
+// is. As long as flush() is only called from one thread, we're fine,
+// but this is a guarantee that the logger module doesn't make.
+pub struct WriteWrapper<W> {
+    w: W,
+}
+impl<W> WriteWrapper<W>
+where
+    W: serial::Write<u8>,
+{
+    pub const fn new(writer: W) -> Self {
+        Self { w: writer }
+    }
+}
+unsafe impl<W> Sync for WriteWrapper<W> {}
+
+pub struct SerialLogger<W, L> {
+    writer: UnsafeCell<WriteWrapper<W>>,
+    led: UnsafeCell<L>,
+}
+
+impl<W, L> SerialLogger<W, L>
+where
+    W: serial::Write<u8>,
+    L: OutputPin + Send + Sync,
+{
+    pub fn new(writer: WriteWrapper<W>, led: L) -> Self {
+        // Stash this for unsafe usage in case there's an issue with
+        // the rest of the logging.
+        unsafe { UART0 = core::mem::transmute(&writer.w) };
+        Self {
+            writer: UnsafeCell::new(writer),
+            led: UnsafeCell::new(led),
+        }
+    }
+}
+unsafe impl<W, L> Send for SerialLogger<W, L> {}
+unsafe impl<W, L> Sync for SerialLogger<W, L> {}
+
+impl<W, L> log::Log for SerialLogger<W, L>
+where
+    W: serial::Write<u8>,
+    L: OutputPin + Send + Sync,
+{
+    fn enabled(&self, metadata: &Metadata) -> bool {
+        metadata.level() <= log::max_level()
+    }
+
+    fn log(&self, record: &Record) {
+        if !self.enabled(record.metadata()) {
+            return;
+        }
+
+        let jrb = unsafe { &mut JRB };
+        write!(
+            jrb,
+            "[{}] {} {} -- {}\r\n",
+            rtc::millis(),
+            record.level(),
+            record.target(),
+            record.args()
+        )
+        .ok();
+    }
+
+    fn flush(&self) {
+        // Unsafe due to mutable static. We can only deal with the
+        // tail position of the buffer here to keep things safe.
+        let jrb = unsafe { &mut JRB };
+        if jrb.lbr.is_empty() {
+            return;
+        }
+
+        let led = unsafe { &mut (*self.led.get()) };
+        let writer = unsafe { &mut (*self.writer.get()) };
+
+        led.set_high().ok();
+        while let Some(b) = jrb.lbr.shift() {
+            nb::block!(writer.w.write(b)).ok();
+        }
+        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");
+    }
+}