esp32/usb: Wake main thread when usb receives data.

This improves latency on stdin.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

ports/esp32/usb.c

@@ -41,7 +41,8 @@
 static uint8_t usb_rx_buf[CONFIG_TINYUSB_CDC_RX_BUFSIZE];
 
 static void usb_callback_rx(int itf, cdcacm_event_t *event) {
-    // TODO: what happens if more chars come in during this function, are they lost?
+    // IDF places tinyusb rx data onto freertos ringbuffer which this function
+    // forwards onto the stdin_ringbuf
     for (;;) {
         size_t len = 0;
         esp_err_t ret = tinyusb_cdcacm_read(itf, usb_rx_buf, sizeof(usb_rx_buf), &len);
@@ -58,6 +59,7 @@ static void usb_callback_rx(int itf, cdcacm_event_t *event) {
                 ringbuf_put(&stdin_ringbuf, usb_rx_buf[i]);
             }
         }
+        xTaskNotifyGive(mp_main_task_handle);
     }
 }