From d13c53906ffba1495f49fcf90f1f3260bb17703f Mon Sep 17 00:00:00 2001
From: Brian Cully <bjc@kublai.com>
Date: Sun, 28 Jul 2019 12:12:41 -0400
Subject: Add pipe::NO_DATA_STAGE const for convenience.

For use in `control_req`'s buffer argument if no data stage is
required. It was either this or have a separate function.
---
 usbh/src/device.rs | 6 +++---
 usbh/src/lib.rs    | 4 ++--
 usbh/src/pipe.rs   | 7 ++++++-
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/usbh/src/device.rs b/usbh/src/device.rs
index eeaa33b..bdb993e 100644
--- a/usbh/src/device.rs
+++ b/usbh/src/device.rs
@@ -1,4 +1,4 @@
-use super::pipe::{Pipe, PipeErr, PipeTable};
+use super::pipe::{Pipe, PipeErr, PipeTable, NO_DATA_STAGE};
 use super::usbproto::*;
 
 use core::convert::TryInto;
@@ -199,7 +199,7 @@ impl Device {
                     RequestCode::SetConfiguration,
                     WValue::from((conf, 0)),
                     0,
-                    Option::<&mut ()>::None,
+                    NO_DATA_STAGE,
                     self.millis,
                 )?;
                 debug!(" -- configuration set");
@@ -214,7 +214,7 @@ impl Device {
                     RequestCode::GetInterface, // This is also idle, but can't have two enums with the same value.
                     WValue::from((0, 0)),
                     0,
-                    Option::<&mut ()>::None,
+                    NO_DATA_STAGE,
                     self.millis,
                 )?;
                 debug!(" -- idle set");
diff --git a/usbh/src/lib.rs b/usbh/src/lib.rs
index 94230b2..70acc31 100755
--- a/usbh/src/lib.rs
+++ b/usbh/src/lib.rs
@@ -6,7 +6,7 @@ mod pipe;
 mod usbproto;
 
 use device::DeviceTable;
-use pipe::{PipeErr, PipeTable, USBPipeType};
+use pipe::{PipeErr, PipeTable, USBPipeType, NO_DATA_STAGE};
 use rb::{Reader, RingBuffer, Writer};
 use usbproto::*;
 
@@ -383,7 +383,7 @@ where
                     RequestCode::SetAddress,
                     WValue::from((device.addr, 0)),
                     0,
-                    Option::<&mut ()>::None,
+                    NO_DATA_STAGE,
                     self.millis,
                 )?;
 
diff --git a/usbh/src/pipe.rs b/usbh/src/pipe.rs
index 3dab629..388b518 100644
--- a/usbh/src/pipe.rs
+++ b/usbh/src/pipe.rs
@@ -21,14 +21,19 @@ use atsamd_hal::target_device::usb::{
 use core::convert::TryInto;
 use log::{debug, trace};
 
-// TODO: verify this timeout against §9.2.6.1 of USB 2.0 spec.
+// Maximum time to wait for a control request with data to finish. cf
+// §9.2.6.1 of USB 2.0.
 const USB_TIMEOUT: usize = 5 * 1024; // 5 Seconds
 
 // samd21 only supports 8 pipes.
 const MAX_PIPES: usize = 8;
 
+// How many times to retry a transaction that has transient errors.
 const NAK_LIMIT: usize = 15;
 
+// For use in control requests that do not require a data stage.
+pub(crate) const NO_DATA_STAGE: Option<&mut ()> = None;
+
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub(crate) enum PipeErr {
     ShortPacket,
-- 
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