usbd: clear endpoint busy/claimed when a completion event is dropped

An XFER_COMPLETE dropped by a full event queue leaves its endpoint's
BUSY|CLAIMED state set forever - the consumer that normally clears it
never sees the event, so usbd_edpt_claim()/usbd_edpt_xfer() fail from
then on and the class never re-arms the endpoint. Clear both flags when
the enqueue fails: the completion is lost either way, but the endpoint
stays usable.

Unit test: arm a bulk endpoint, drop its completion against a full
queue, verify the endpoint can be claimed and re-armed.

1 files changed, 12 insertions, 4 deletions

diff --git a/src/device/usbd.c b/src/device/usbd.c
index 79802e70f..f5c3046d6 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -1475,10 +1475,18 @@ TU_ATTR_FAST_FUNC void dcd_event_handler(dcd_event_t const* event, bool in_isr)
       break;
   }
 
-  if (send && !queue_event(event, in_isr) && event->event_id == DCD_EVENT_SETUP_RECEIVED) {
-    // dropped by a full queue: undo the increment, else every later SETUP is skipped as
-    // "other SETUP in queue" and EP0 is deaf until re-init
-    _usbd_queued_setup--;
+  if (send && !queue_event(event, in_isr)) {
+    // event dropped by a full queue: undo state that would otherwise wedge permanently
+    if (event->event_id == DCD_EVENT_SETUP_RECEIVED) {
+      // undo the increment, else every later SETUP is skipped as "other SETUP in queue"
+      // and EP0 is deaf until re-init
+      _usbd_queued_setup--;
+    } else if (event->event_id == DCD_EVENT_XFER_COMPLETE) {
+      // clear busy + claimed, else the endpoint can never be claimed or re-armed again
+      uint8_t const epnum = tu_edpt_number(event->xfer_complete.ep_addr);
+      uint8_t const ep_dir = tu_edpt_dir(event->xfer_complete.ep_addr);
+      _usbd_dev.ep_status[epnum][ep_dir] &= (uint8_t) ~(TU_EDPT_STATE_BUSY | TU_EDPT_STATE_CLAIMED);
+    }
   }
 }