Fixed error, when host send some buffer, less then minimum.

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

@@ -882,6 +882,18 @@ uint8_t  USBD_CDC_ReceivePacket(USBD_HandleTypeDef *pdev)
   }
 }
 
+uint8_t USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev)
+{
+  /* Suspend or Resume USB Out process */
+  if (pdev->pClassData != NULL) {
+    /* Prepare Out endpoint to receive next packet */
+    USBD_LL_PrepareReceive(pdev, CDC_OUT_EP, 0, 0);
+    return USBD_OK;
+  } else {
+    return USBD_FAIL;
+  }
+}
+
 #endif /* USBD_USE_CDC */
 #endif /* USBCON */
 /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

cores/arduino/stm32/usb/cdc/usbd_cdc.h

@@ -156,6 +156,8 @@ uint8_t  USBD_CDC_SetRxBuffer(USBD_HandleTypeDef   *pdev,
 
 uint8_t  USBD_CDC_ReceivePacket(USBD_HandleTypeDef *pdev);
 
+uint8_t  USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev);
+
 uint8_t  USBD_CDC_TransmitPacket(USBD_HandleTypeDef *pdev);
 /**
   * @}

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

@@ -205,7 +205,9 @@ static int8_t USBD_CDC_Receive(uint8_t *Buf, uint32_t *Len)
   CDC_ReceiveQueue_CommitBlock(&ReceiveQueue, (uint16_t)(*Len));
   receivePended = false;
   /* If enough space in the queue for a full buffer then continue receive */
-  CDC_resume_receive();
+  if (!CDC_resume_receive()) {
+    USBD_CDC_ClearBuffer(&hUSBD_Device_CDC);
+  }
   return USBD_OK;
 }
 
@@ -271,7 +273,7 @@ void CDC_continue_transmit(void)
   }
 }
 
-void CDC_resume_receive(void)
+bool CDC_resume_receive(void)
 {
   /*
    * TS: main and IRQ threads can't pass it at same time, because
@@ -284,7 +286,9 @@ void CDC_resume_receive(void)
       /* Set new buffer */
       USBD_CDC_SetRxBuffer(&hUSBD_Device_CDC, block);
       USBD_CDC_ReceivePacket(&hUSBD_Device_CDC);
+      return true;
     }
+    return false;
   }
 }
 

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

@@ -47,7 +47,7 @@ extern CDC_ReceiveQueue_TypeDef ReceiveQueue;
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */
 void CDC_continue_transmit(void);
-void CDC_resume_receive(void);
+bool CDC_resume_receive(void);
 void CDC_init(void);
 void CDC_deInit(void);