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This PR updates the traits to allow poll() to return Result<> types if needed. I'm unsure if the UsbClass::poll() function should return a Result or not currently.

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I think this PR makes sense because currently there's no way to return an error from the driver. Using PollResult::None in such situations is ambiguous.

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@ianrrees ianrrees left a comment

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I like this change, in particular because it encourages users to think about how to handle the return value of poll() - in most of the examples I've seen it is just ignored.

@@ -228,15 +228,17 @@ impl<B: UsbBus> UsbDevice<'_, B> {

match req {
Some(req) if req.direction == UsbDirection::In => {
if let Err(_err) = self.control_in(classes, req) {
if let Err(err) = self.control_in(classes, req) {
// TODO: Propagate error out of `poll()`
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This comment should go away with the PR, the same appears in a couple more places below.

@@ -317,10 +319,10 @@ impl<B: UsbBus> UsbDevice<'_, B> {
}

for cls in classes.iter_mut() {
cls.poll();
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@ianrrees ianrrees Mar 5, 2025

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This introduces a subtle change in behaviour that maybe should be documented: if there are multiple classes and an earlier one errors out, the later classes won't be polled.

However, looking at the current implementation and docstring, it's not explicit that polling the device (sometimes... unclear if that's correct per #32) results in the classes being polled.

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3 participants