虚拟串口与STM32通信遇到的疑问求解

我想要一个虚拟串口与STM32通信。
在其中，我需要从串口获取输入命令，然后实现命令想要做的事情。

我在网上看到很多关于它的例子。 然而，它们都在“CDC_Receive_FS”中获得消息并立即重新发送到PC。 这意味着消息没有出去。 例如，离开“usbd_cdc_if.c”并在“main.c”中发送给PC。

如何在“CDC_Receive_FS”外部收到消息？

如何避免丢失消息？

usbd_cdc_if.c

• /**
  
•   * @brief  Data received over USB OUT endpoint are sent over CDC interface
  
•   *         through this function.
  
•   *
  
•   *         @note
  
•   *         This function will block any OUT packet reception on USB endpoint
  
•   *         untill exiting this function. If you exit this function before transfer
  
•   *         is complete on CDC interface (ie. using DMA controller) it will result
  
•   *         in receiving more data while previous ones are still not sent.
  
•   *
  
•   * @param  Buf: Buffer of data to be received
  
•   * @param  Len: Number of data received (in bytes)
  
•   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
  
•   */
  
• static int8_t CDC_Receive_FS(uint8_t* Buf, uint32_t *Len)
  
• {
  
•   /* USER CODE BEGIN 6 */
  
•   USBD_CDC_SetRxBuffer( hUsbDeviceFS,  Buf[0]);
  
•   USBD_CDC_ReceivePacket( hUsbDeviceFS);
  
• 
  
•   USBD_CDC_SetTxBuffer( hUsbDeviceFS, Buf, Len);
  
•   USBD_CDC_TransmitPacket( hUsbDeviceFS);
  
• 
  
•   return (USBD_OK);
  
•   /* USER CODE END 6 */
  
• }
  

如何在main.c中使用“UserRxBufferFS”和“UserTxBufferFS”？

• /** @defgroup USBD_CDC_IF_Private_Variables USBD_CDC_IF_Private_Variables
  
•   * @brief Private variables.
  
•   * @{
  
•   */
  
• /* Create buffer for reception and transmission           */
  
• /* It's up to user to redefine and/or remove those define */
  
• /** Received data over USB are stored in this buffer      */
  
• uint8_t UserRxBufferFS[APP_RX_DATA_SIZE];
  
• 
  
• /** Data to send over USB CDC are stored in this buffer   */
  
• uint8_t UserTxBufferFS[APP_TX_DATA_SIZE];
  

[/td]
以下内容为评论
[td]我正在使用Blue Pill板。

我在下面找到了例子。它教我成功在外面使用“UserRxBufferFS”和“* Len”。

• 
  
• /**
  
•   ******************************************************************************
  
•   * @file           : main.c
  
•   * @brief          : Main program body
  
•   ******************************************************************************
  
•   * This notice applies to any and all portions of this file
  
•   * that are not between comment pairs USER CODE BEGIN and
  
•   * USER CODE END. Other portions of this file, whether
  
•   * inserted by the user or by software development tools
  
•   * are owned by their respective copyright owners.
  
•   *
  
•   * Copyright (c) 2018 STMicroelectronics International N.V.
  
•   * All rights reserved.
  
•   *
  
•   * Redistribution and use in source and binary forms, with or without
  
•   * modification, are permitted, provided that the following conditions are met:
  
•   *
  
•   * 1. Redistribution of source code must retain the above copyright notice,
  
•   *    this list of conditions and the following disclaimer.
  
•   * 2. Redistributions in binary form must reproduce the above copyright notice,
  
•   *    this list of conditions and the following disclaimer in the documentation
  
•   *    and/or other materials provided with the distribution.
  
•   * 3. Neither the name of STMicroelectronics nor the names of other
  
•   *    contributors to this software may be used to endorse or promote products
  
•   *    derived from this software without specific written permission.
  
•   * 4. This software, including modifications and/or derivative works of this
  
•   *    software, must execute solely and exclusively on microcontroller or
  
•   *    microprocessor devices manufactured by or for STMicroelectronics.
  
•   * 5. Redistribution and use of this software other than as permitted under
  
•   *    this license is void and will automatically terminate your rights under
  
•   *    this license.
  
•   *
  
•   * THIS SOFTWARE IS PROVIDED BY STMICROELECTRONICS AND CONTRIBUTORS "AS IS"
  
•   * AND ANY EXPRESS, IMPLIED OR STATUTORY WARRANTIES, INCLUDING, BUT NOT
  
•   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  
•   * PARTICULAR PURPOSE AND NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY
  
•   * RIGHTS ARE DISCLAIMED TO THE FULLEST EXTENT PERMITTED BY LAW. IN NO EVENT
  
•   * SHALL STMICROELECTRONICS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  
•   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  
•   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
  
•   * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  
•   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  
•   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
  
•   * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
•   *
  
•   ******************************************************************************
  
•   */
  
• /* Includes ------------------------------------------------------------------*/
  
• #include "main.h"
  
• #include "stm32f1xx_hal.h"
  
• #include "usart.h"
  
• #include "usb_device.h"
  
• #include "gpio.h"
  
• 
  
• /* USER CODE BEGIN Includes */
  
• 
  
• #include "usb_device.h"
  
• #include "usbd_core.h"
  
• #include "usbd_desc.h"
  
• #include "usbd_cdc.h"
  
• #include "usbd_cdc_if.h"
  
• /* USER CODE END Includes */
  
• 
  
• /* Private variables ---------------------------------------------------------*/
  
• 
  
• /* USER CODE BEGIN PV */
  
• /* Private variables ---------------------------------------------------------*/
  
• // http://www.smilefrog.net/?p=763  "USB-CDC (VCP)“
  
• extern uint8_t UserRxBufferFS[];  // declare receive data external variable
  
• extern uint8_t DataLen;  // declare receive buffer external variable
  
• /* USER CODE END PV */
  
• 
  
• /* Private function prototypes -----------------------------------------------*/
  
• void SystemClock_Config(void);
  
• 
  
• /* USER CODE BEGIN PFP */
  
• /* Private function prototypes -----------------------------------------------*/
  
• 
  
• /* USER CODE END PFP */
  
• 
  
• /* USER CODE BEGIN 0 */
  
• 
  
• /* USER CODE END 0 */
  
• 
  
• /**
  
•   * @brief  The application entry point.
  
•   *
  
•   * @retval None
  
•   */
  
• int main(void)
  
• {
  
•   /* USER CODE BEGIN 1 */
  
• 
  
•   /* USER CODE END 1 */
  
• 
  
•   /* MCU Configuration----------------------------------------------------------*/
  
• 
  
•   /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  
•   HAL_Init();
  
• 
  
•   /* USER CODE BEGIN Init */
  
• 
  
•   /* USER CODE END Init */
  
• 
  
•   /* Configure the system clock */
  
•   SystemClock_Config();
  
• 
  
•   /* USER CODE BEGIN SysInit */
  
• 
  
•   /* USER CODE END SysInit */
  
• 
  
•   /* Initialize all configured peripherals */
  
•   MX_GPIO_Init();
  
•   MX_USART1_UART_Init();
  
•   MX_USB_DEVICE_Init();
  
•   /* USER CODE BEGIN 2 */
  
• 
  
•   /* USER CODE END 2 */
  
• 
  
•   /* Infinite loop */
  
•   /* USER CODE BEGIN WHILE */
  
•   while (1)
  
•   {
  
• 
  
•   /* USER CODE END WHILE */
  
• 
  
•   /* USER CODE BEGIN 3 */
  
•           /* to ensure the code is running */
  
•           //HAL_GPIO_TogglePin(GPIOB, GPIO_PIN_12);
  
•           //HAL_Delay(1000);
  
• 
  
•           if(DataLen > 0)
  
•           {
  
•                   while(CDC_Transmit_FS(UserRxBufferFS, DataLen));
  
•                   DataLen = 0;
  
•           }
  
•   }
  
•   /* USER CODE END 3 */
  
• 
  
• }
  
• 
  
• /**
  
•   * @brief System Clock Configuration
  
•   * @retval None
  
•   */
  
• void SystemClock_Config(void)
  
• {
  
• 
  
•   RCC_OscInitTypeDef RCC_OscInitStruct;
  
•   RCC_ClkInitTypeDef RCC_ClkInitStruct;
  
•   RCC_PeriphCLKInitTypeDef PeriphClkInit;
  
• 
  
•     /**Initializes the CPU, AHB and APB busses clocks
  
•     */
  
•   RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  
•   RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  
•   RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  
•   RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  
•   RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  
•   RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  
•   RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  
•   if (HAL_RCC_OscConfig( RCC_OscInitStruct) != HAL_OK)
  
•   {
  
•     _Error_Handler(__FILE__, __LINE__);
  
•   }
  
• 
  
•     /**Initializes the CPU, AHB and APB busses clocks
  
•     */
  
•   RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
  
•                               |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  
•   RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  
•   RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  
•   RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
  
•   RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  
• 
  
•   if (HAL_RCC_ClockConfig( RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  
•   {
  
•     _Error_Handler(__FILE__, __LINE__);
  
•   }
  
• 
  
•   PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB;
  
•   PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_PLL_DIV1_5;
  
•   if (HAL_RCCEx_PeriphCLKConfig( PeriphClkInit) != HAL_OK)
  
•   {
  
•     _Error_Handler(__FILE__, __LINE__);
  
•   }
  
• 
  
•     /**Configure the Systick interrupt time
  
•     */
  
•   HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
  
• 
  
•     /**Configure the Systick
  
•     */
  
•   HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
  
• 
  
•   /* SysTick_IRQn interrupt configuration */
  
•   HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
  
• }
  
• 
  
• /* USER CODE BEGIN 4 */
  
• 
  
• /* USER CODE END 4 */
  
• 
  
• /**
  
•   * @brief  This function is executed in case of error occurrence.
  
•   * @param  file: The file name as string.
  
•   * @param  line: The line in file as a number.
  
•   * @retval None
  
•   */
  
• void _Error_Handler(char *file, int line)
  
• {
  
•   /* USER CODE BEGIN Error_Handler_Debug */
  
•   /* User can add his own implementation to report the HAL error return state */
  
•   while(1)
  
•   {
  
•   }
  
•   /* USER CODE END Error_Handler_Debug */
  
• }
  
• 
  
• #ifdef  USE_FULL_ASSERT
  
• /**
  
•   * @brief  Reports the name of the source file and the source line number
  
•   *         where the assert_param error has occurred.
  
•   * @param  file: pointer to the source file name
  
•   * @param  line: assert_param error line source number
  
•   * @retval None
  
•   */
  
• void assert_failed(uint8_t* file, uint32_t line)
  
• {
  
•   /* USER CODE BEGIN 6 */
  
•   /* User can add his own implementation to report the file name and line number,
  
•      tex: printf("Wrong parameters value: file %s on line %drn", file, line) */
  
•   /* USER CODE END 6 */
  
• }
  
• #endif /* USE_FULL_ASSERT */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/
  

复制代码

• /**
  
•   ******************************************************************************
  
•   * @file           : usbd_cdc_if.c///
  
•   * @version        : v2.0_Cube
  
•   * @brief          : Usb device for Virtual Com Port.
  
•   ******************************************************************************
  
•   * This notice applies to any and all portions of this file
  
•   * that are not between comment pairs USER CODE BEGIN and
  
•   * USER CODE END. Other portions of this file, whether
  
•   * inserted by the user or by software development tools
  
•   * are owned by their respective copyright owners.
  
•   *
  
•   * Copyright (c) 2018 STMicroelectronics International N.V.
  
•   * All rights reserved.
  
•   *
  
•   * Redistribution and use in source and binary forms, with or without
  
•   * modification, are permitted, provided that the following conditions are met:
  
•   *
  
•   * 1. Redistribution of source code must retain the above copyright notice,
  
•   *    this list of conditions and the following disclaimer.
  
•   * 2. Redistributions in binary form must reproduce the above copyright notice,
  
•   *    this list of conditions and the following disclaimer in the documentation
  
•   *    and/or other materials provided with the distribution.
  
•   * 3. Neither the name of STMicroelectronics nor the names of other
  
•   *    contributors to this software may be used to endorse or promote products
  
•   *    derived from this software without specific written permission.
  
•   * 4. This software, including modifications and/or derivative works of this
  
•   *    software, must execute solely and exclusively on microcontroller or
  
•   *    microprocessor devices manufactured by or for STMicroelectronics.
  
•   * 5. Redistribution and use of this software other than as permitted under
  
•   *    this license is void and will automatically terminate your rights under
  
•   *    this license.
  
•   *
  
•   * THIS SOFTWARE IS PROVIDED BY STMICROELECTRONICS AND CONTRIBUTORS "AS IS"
  
•   * AND ANY EXPRESS, IMPLIED OR STATUTORY WARRANTIES, INCLUDING, BUT NOT
  
•   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  
•   * PARTICULAR PURPOSE AND NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY
  
•   * RIGHTS ARE DISCLAIMED TO THE FULLEST EXTENT PERMITTED BY LAW. IN NO EVENT
  
•   * SHALL STMICROELECTRONICS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  
•   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  
•   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
  
•   * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  
•   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  
•   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
  
•   * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
•   *
  
•   ******************************************************************************
  
•   */
  
• 
  
• /* Includes ------------------------------------------------------------------*/
  
• #include "usbd_cdc_if.h"
  
• 
  
• /* USER CODE BEGIN INCLUDE */
  
• 
  
• /* USER CODE END INCLUDE */
  
• 
  
• /* Private typedef -----------------------------------------------------------*/
  
• /* Private define ------------------------------------------------------------*/
  
• /* Private macro -------------------------------------------------------------*/
  
• 
  
• /* USER CODE BEGIN PV */
  
• /* Private variables ---------------------------------------------------------*/
  
• 
  
• /* USER CODE END PV */
  
• 
  
• /** @addtogroup STM32_USB_OTG_DEVICE_LIBRARY
  
•   * @brief Usb device library.
  
•   * @{
  
•   */
  
• 
  
• /** @addtogroup USBD_CDC_IF
  
•   * @{
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Private_TypesDefinitions USBD_CDC_IF_Private_TypesDefinitions
  
•   * @brief Private types.
  
•   * @{
  
•   */
  
• 
  
• /* USER CODE BEGIN PRIVATE_TYPES */
  
• 
  
• /* USER CODE END PRIVATE_TYPES */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Private_Defines USBD_CDC_IF_Private_Defines
  
•   * @brief Private defines.
  
•   * @{
  
•   */
  
• 
  
• /* USER CODE BEGIN PRIVATE_DEFINES */
  
• /* Define size for the receive and transmit buffer over CDC */
  
• /* It's up to user to redefine and/or remove those define */
  
• #define APP_RX_DATA_SIZE  64
  
• #define APP_TX_DATA_SIZE  64
  
• /* USER CODE END PRIVATE_DEFINES */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Private_Macros USBD_CDC_IF_Private_Macros
  
•   * @brief Private macros.
  
•   * @{
  
•   */
  
• 
  
• /* USER CODE BEGIN PRIVATE_MACRO */
  
• 
  
• /* USER CODE END PRIVATE_MACRO */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Private_Variables USBD_CDC_IF_Private_Variables
  
•   * @brief Private variables.
  
•   * @{
  
•   */
  
• /* Create buffer for reception and transmission           */
  
• /* It's up to user to redefine and/or remove those define */
  
• /** Received data over USB are stored in this buffer      */
  
• uint8_t UserRxBufferFS[APP_RX_DATA_SIZE];
  
• 
  
• /** Data to send over USB CDC are stored in this buffer   */
  
• uint8_t UserTxBufferFS[APP_TX_DATA_SIZE];
  
• 
  
• /* USER CODE BEGIN PRIVATE_VARIABLES */
  
• // http://www.smilefrog.net/?p=763  "USB-CDC (VCP)“
  
• uint8_t DataLen; // define receive buffer length variable
  
• /* USER CODE END PRIVATE_VARIABLES */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Exported_Variables USBD_CDC_IF_Exported_Variables
  
•   * @brief Public variables.
  
•   * @{
  
•   */
  
• 
  
• extern USBD_HandleTypeDef hUsbDeviceFS;
  
• 
  
• /* USER CODE BEGIN EXPORTED_VARIABLES */
  
• 
  
• /* USER CODE END EXPORTED_VARIABLES */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /** @defgroup USBD_CDC_IF_Private_FunctionPrototypes USBD_CDC_IF_Private_FunctionPrototypes
  
•   * @brief Private functions declaration.
  
•   * @{
  
•   */
  
• 
  
• static int8_t CDC_Init_FS(void);
  
• static int8_t CDC_DeInit_FS(void);
  
• static int8_t CDC_Control_FS(uint8_t cmd, uint8_t* pbuf, uint16_t length);
  
• static int8_t CDC_Receive_FS(uint8_t* pbuf, uint32_t *Len);
  
• 
  
• /* USER CODE BEGIN PRIVATE_FUNCTIONS_DECLARATION */
  
• 
  
• /* USER CODE END PRIVATE_FUNCTIONS_DECLARATION */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• USBD_CDC_ItfTypeDef USBD_Interface_fops_FS =
  
• {
  
•   CDC_Init_FS,
  
•   CDC_DeInit_FS,
  
•   CDC_Control_FS,
  
•   CDC_Receive_FS
  
• };
  
• 
  
• /* Private functions ---------------------------------------------------------*/
  
• /**
  
•   * @brief  Initializes the CDC media low layer over the FS USB IP
  
•   * @retval USBD_OK if all operations are OK else USBD_FAIL
  
•   */
  
• static int8_t CDC_Init_FS(void)
  
• {
  
•   /* USER CODE BEGIN 3 */
  
•   /* Set Application Buffers */
  
•   USBD_CDC_SetTxBuffer( hUsbDeviceFS, UserTxBufferFS, 0);
  
•   USBD_CDC_SetRxBuffer( hUsbDeviceFS, UserRxBufferFS);
  
•   return (USBD_OK);
  
•   /* USER CODE END 3 */
  
• }
  
• 
  
• /**
  
•   * @brief  DeInitializes the CDC media low layer
  
•   * @retval USBD_OK if all operations are OK else USBD_FAIL
  
•   */
  
• static int8_t CDC_DeInit_FS(void)
  
• {
  
•   /* USER CODE BEGIN 4 */
  
•   return (USBD_OK);
  
•   /* USER CODE END 4 */
  
• }
  
• 
  
• /**
  
•   * @brief  Manage the CDC class requests
  
•   * @param  cmd: Command code
  
•   * @param  pbuf: Buffer containing command data (request parameters)
  
•   * @param  length: Number of data to be sent (in bytes)
  
•   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
  
•   */
  
• static int8_t CDC_Control_FS(uint8_t cmd, uint8_t* pbuf, uint16_t length)
  
• {
  
•   /* USER CODE BEGIN 5 */
  
•   switch(cmd)
  
•   {
  
•     case CDC_SEND_ENCAPSULATED_COMMAND:
  
• 
  
•     break;
  
• 
  
•     case CDC_GET_ENCAPSULATED_RESPONSE:
  
• 
  
•     break;
  
• 
  
•     case CDC_SET_COMM_FEATURE:
  
• 
  
•     break;
  
• 
  
•     case CDC_GET_COMM_FEATURE:
  
• 
  
•     break;
  
• 
  
•     case CDC_CLEAR_COMM_FEATURE:
  
• 
  
•     break;
  
• 
  
•   /*******************************************************************************/
  
•   /* Line Coding Structure                                                       */
  
•   /*-----------------------------------------------------------------------------*/
  
•   /* Offset | Field       | Size | Value  | Description                          */
  
•   /* 0      | dwDTERate   |   4  | Number |Data terminal rate, in bits per second*/
  
•   /* 4      | bCharFormat |   1  | Number | Stop bits                            */
  
•   /*                                        0 - 1 Stop bit                       */
  
•   /*                                        1 - 1.5 Stop bits                    */
  
•   /*                                        2 - 2 Stop bits                      */
  
•   /* 5      | bParityType |  1   | Number | Parity                               */
  
•   /*                                        0 - None                             */
  
•   /*                                        1 - Odd                              */
  
•   /*                                        2 - Even                             */
  
•   /*                                        3 - Mark                             */
  
•   /*                                        4 - Space                            */
  
•   /* 6      | bDataBits  |   1   | Number Data bits (5, 6, 7, 8 or 16).          */
  
•   /*******************************************************************************/
  
•     case CDC_SET_LINE_CODING:
  
• 
  
•     break;
  
• 
  
•     case CDC_GET_LINE_CODING:
  
• 
  
•     break;
  
• 
  
•     case CDC_SET_CONTROL_LINE_STATE:
  
• 
  
•     break;
  
• 
  
•     case CDC_SEND_BREAK:
  
• 
  
•     break;
  
• 
  
•   default:
  
•     break;
  
•   }
  
• 
  
•   return (USBD_OK);
  
•   /* USER CODE END 5 */
  
• }
  
• 
  
• /**
  
•   * @brief  Data received over USB OUT endpoint are sent over CDC interface
  
•   *         through this function.
  
•   *
  
•   *         @note
  
•   *         This function will block any OUT packet reception on USB endpoint
  
•   *         untill exiting this function. If you exit this function before transfer
  
•   *         is complete on CDC interface (ie. using DMA controller) it will result
  
•   *         in receiving more data while previous ones are still not sent.
  
•   *
  
•   * @param  Buf: Buffer of data to be received
  
•   * @param  Len: Number of data received (in bytes)
  
•   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
  
•   */
  
• static int8_t CDC_Receive_FS(uint8_t* Buf, uint32_t *Len)
  
• {
  
•   /* USER CODE BEGIN 6 */
  
•   USBD_CDC_SetRxBuffer( hUsbDeviceFS,  Buf[0]);
  
•   USBD_CDC_ReceivePacket( hUsbDeviceFS);
  
• 
  
•   DataLen = *Len; //assign receive buffer length, don't edit any other!!!
  
• 
  
•   return (USBD_OK);
  
•   /* USER CODE END 6 */
  
• }
  
• 
  
• /**
  
•   * @brief  CDC_Transmit_FS
  
•   *         Data to send over USB IN endpoint are sent over CDC interface
  
•   *         through this function.
  
•   *         @note
  
•   *
  
•   *
  
•   * @param  Buf: Buffer of data to be sent
  
•   * @param  Len: Number of data to be sent (in bytes)
  
•   * @retval USBD_OK if all operations are OK else USBD_FAIL or USBD_BUSY
  
•   */
  
• uint8_t CDC_Transmit_FS(uint8_t* Buf, uint16_t Len)
  
• {
  
•   uint8_t result = USBD_OK;
  
•   /* USER CODE BEGIN 7 */
  
•   USBD_CDC_HandleTypeDef *hcdc = (USBD_CDC_HandleTypeDef*)hUsbDeviceFS.pClassData;
  
•   if (hcdc->TxState != 0){
  
•     return USBD_BUSY;
  
•   }
  
•   USBD_CDC_SetTxBuffer( hUsbDeviceFS, Buf, Len);
  
•   result = USBD_CDC_TransmitPacket( hUsbDeviceFS);
  
•   /* USER CODE END 7 */
  
•   return result;
  
• }
  
• 
  
• /* USER CODE BEGIN PRIVATE_FUNCTIONS_IMPLEMENTATION */
  
• 
  
• /* USER CODE END PRIVATE_FUNCTIONS_IMPLEMENTATION */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /**
  
•   * @}
  
•   */
  
• 
  
• /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/
  

复制代码

问题1。
为什么使用“while（CDC_Transmit_FS（UserRxBufferFS，DataLen））;”？
我尝试只使用“CDC_Transmit_FS（UserRxBufferFS，DataLen）”，它似乎也有用。
它与下一步“DataLen = 0”（重置DataLen）有关吗？

问题2。
只有当我在主循环中添加一些延迟（以模拟另一个任务）时，它会丢失消息或只是回转最后一个字。
如何避免丢失？

请指教！