Add check if the last packet we tried to transfer is dragging for too

long.

cores/arduino/stm32/usb/cdc/usbd_cdc_if.c

@@ -32,6 +32,8 @@
 #define CDC_MAX_PACKET_SIZE USB_MAX_EP0_SIZE
 #endif
 
+#define USB_CDC_TRANSMIT_TIMEOUT 3
+
 /* USBD_CDC Private Variables */
 /* USB Device Core CDC handle declaration */
 USBD_HandleTypeDef hUSBD_Device_CDC;
@@ -43,6 +45,7 @@ CDC_TransmitQueue_TypeDef TransmitQueue;
 CDC_ReceiveQueue_TypeDef ReceiveQueue;
 __IO uint32_t lineState = 0;
 __IO bool receivePended = true;
+static uint32_t transmitStart = 0;
 
 
 /** USBD_CDC Private Function Prototypes */
@@ -212,6 +215,7 @@ static int8_t USBD_CDC_Receive(uint8_t *Buf, uint32_t *Len)
 
 static int8_t USBD_CDC_Transferred(void)
 {
+  transmitStart = 0;
   CDC_TransmitQueue_CommitRead(&TransmitQueue);
   CDC_continue_transmit();
   return (USBD_OK);
@@ -247,7 +251,13 @@ void CDC_deInit(void)
 
 bool CDC_connected()
 {
-  return hUSBD_Device_CDC.dev_state == USBD_STATE_CONFIGURED && lineState;
+  uint32_t transmitTime = 0;
+  if (transmitStart) {
+    transmitTime = HAL_GetTick() - transmitStart;
+  }
+  return hUSBD_Device_CDC.dev_state == USBD_STATE_CONFIGURED
+    && transmitTime < USB_CDC_TRANSMIT_TIMEOUT
+    && lineState;
 }
 
 void CDC_continue_transmit(void)