diff --git a/ports/esp32/usb.c b/ports/esp32/usb.c
index 2e417755c..316482e18 100644
--- a/ports/esp32/usb.c
+++ b/ports/esp32/usb.c
@@ -40,8 +40,10 @@
 
 static uint8_t usb_rx_buf[CONFIG_TINYUSB_CDC_RX_BUFSIZE];
 
+// This is called from FreeRTOS task "tusb_tsk" in espressif__esp_tinyusb (not an ISR).
 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?
+    // espressif__esp_tinyusb places tinyusb rx data onto freertos ringbuffer which
+    // this function forwards onto our 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 +60,7 @@ static void usb_callback_rx(int itf, cdcacm_event_t *event) {
                 ringbuf_put(&stdin_ringbuf, usb_rx_buf[i]);
             }
         }
+        mp_hal_wake_main_task();
     }
 }