shared/tinyusb/mp_usbd_cdc: Fix short CDC TX timeouts.

dpgeorge · dpgeorge · commit 880f7bc0406a · 2024-06-26T14:50:42.000+10:00
The `mp_event_wait_ms()` function may return earlier than the requested
timeout, and if that happens repeatedly (eg due to lots of USB data and
IRQs) then the loop waiting for CDC TX FIFO space to become available may
exit much earlier than MICROPY_HW_USB_CDC_TX_TIMEOUT, even when there is
no space.

Fix this by using `mp_hal_ticks_ms()` to compute a more accurate timeout.

The `basics/int_big_mul.py` test fails on RPI_PICO without this fix.

Signed-off-by: Damien George &lt;damien@micropython.org&gt;
diff --git a/shared/tinyusb/mp_usbd_cdc.c b/shared/tinyusb/mp_usbd_cdc.c
@@ -102,9 +102,9 @@ mp_uint_t mp_usbd_cdc_tx_strn(const char *str, mp_uint_t len) {
             n = CFG_TUD_CDC_EP_BUFSIZE;
         }
         if (tud_cdc_connected()) {
-            int timeout = 0;
             // If CDC port is connected but the buffer is full, wait for up to USC_CDC_TIMEOUT ms.
-            while (n > tud_cdc_write_available() && timeout++ < MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+            mp_uint_t t0 = mp_hal_ticks_ms();
+            while (n > tud_cdc_write_available() && (mp_uint_t)(mp_hal_ticks_ms() - t0) < MICROPY_HW_USB_CDC_TX_TIMEOUT) {
                 mp_event_wait_ms(1);
 
                 // Explicitly run the USB stack as the scheduler may be locked (eg we
