STM32 USB学习笔记5

主机环境：Windows 7 SP1

开发环境：MDK5.14

目标板：STM32F103C8T6

开发库：STM32F1Cube库和STM32_USB_Device_Library

承接前文，对于上层应用而言只剩下CDC类接口文件即usbd_cdc_interface，该文件主要为实现CDC类接口所用到的物理资源以及逻辑资源，需要参考通信设备通用串行总线类定义版本1.2以及PSTN设备通用串行总线通信类子类规范版本1.2，这两个文档都可以在USB组织官网上下载得到，首先看下usbd_cdc_interface.h文件，如下：

/* Define to prevent recursive inclusion -------------------------------------*/
#ifndef __USBD_CDC_IF_H
#define __USBD_CDC_IF_H

/* Includes ------------------------------------------------------------------*/
#include "usbd_cdc.h"

/* Exported types ------------------------------------------------------------*/
/* Exported constants --------------------------------------------------------*/
/* User can use this section to tailor USARTx/UARTx instance used and associated 
   resources */
/* Definition for USARTx clock resources */
#define USARTx                           USART1
#define USARTx_CLK_ENABLE()              __HAL_RCC_USART1_CLK_ENABLE();
#define DMAx_CLK_ENABLE()                __HAL_RCC_DMA1_CLK_ENABLE()
#define USARTx_RX_GPIO_CLK_ENABLE()      __HAL_RCC_GPIOA_CLK_ENABLE()
#define USARTx_TX_GPIO_CLK_ENABLE()      __HAL_RCC_GPIOA_CLK_ENABLE() 

#define USARTx_FORCE_RESET()             __HAL_RCC_USART1_FORCE_RESET()
#define USARTx_RELEASE_RESET()           __HAL_RCC_USART1_RELEASE_RESET()

/* Definition for USARTx Pins */
#define USARTx_TX_PIN                    GPIO_PIN_9
#define USARTx_TX_GPIO_PORT              GPIOA  
#define USARTx_RX_PIN                    GPIO_PIN_10
#define USARTx_RX_GPIO_PORT              GPIOA 

/* Definition for USARTx's NVIC: used for receiving data over Rx pin */
#define USARTx_IRQn                      USART1_IRQn
#define USARTx_IRQHandler                USART1_IRQHandler

/* Definition for USARTx's DMA: used for transmitting data over Tx pin */
#define USARTx_TX_DMA_STREAM             DMA1_Channel4
#define USARTx_RX_DMA_STREAM             DMA1_Channel5

/* Definition for USARTx's NVIC */
#define USARTx_DMA_TX_IRQn               DMA1_Channel4_IRQn
#define USARTx_DMA_RX_IRQn               DMA1_Channel5_IRQn
#define USARTx_DMA_TX_IRQHandler         DMA1_Channel4_IRQHandler
#define USARTx_DMA_RX_IRQHandler         DMA1_Channel5_IRQHandler

/* Definition for TIMx clock resources */
#define TIMx                             TIM3
#define TIMx_CLK_ENABLE                  __HAL_RCC_TIM3_CLK_ENABLE
#define TIMx_FORCE_RESET()               __HAL_RCC_USART1_FORCE_RESET()
#define TIMx_RELEASE_RESET()             __HAL_RCC_USART1_RELEASE_RESET()

/* Definition for TIMx's NVIC */
#define TIMx_IRQn                        TIM3_IRQn
#define TIMx_IRQHandler                  TIM3_IRQHandler

/* Periodically, the state of the buffer "UserTxBuffer" is checked.
   The period depends on CDC_POLLING_INTERVAL */
#define CDC_POLLING_INTERVAL             5 /* in ms. The max is 65 and the min is 1 */

extern USBD_CDC_ItfTypeDef  USBD_CDC_fops;

/* Exported macro ------------------------------------------------------------*/
/* Exported functions ------------------------------------------------------- */
#endif /* __USBD_CDC_IF_H */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

这其中主要是一些物理资源的定义，需要用到一个串口资源(且使用DMA方式发送数据)，一个定时器资源(定时读取从串口接收到的数据并发往USB接口)。这里虽然列出了两个DMA通道，但在实现中只用到了TX的DMA发送一个通道，文件末尾有一个CDC类接口数据结构USBD_CDC_ItfTypeDef，如下：

typedef struct _USBD_CDC_Itf
{
  int8_t (* Init)          (void);
  int8_t (* DeInit)        (void);
  int8_t (* Control)       (uint8_t, uint8_t * , uint16_t);   
  int8_t (* Receive)       (uint8_t *, uint32_t *);  

}USBD_CDC_ItfTypeDef;

有关该结构的说明可以在USB器件库文档中找到，如下：

由上可以看出这里只有OUT传输而没有IN传输，VCP模型很简单就只有简单的收发数据以及一些属性的修改等，因此这里的CDC接口接口内容不多。下面查看一下usbd_cdc_interface.c文件，其内容是CDC类物理以及逻辑接口的具体实现。文件开头申请了两块缓冲区用于数据的收发，如下：

#define APP_RX_DATA_SIZE  2048
#define APP_TX_DATA_SIZE  2048

uint8_t UserRxBuffer[APP_RX_DATA_SIZE];/* Received Data over USB are stored in this buffer */
uint8_t UserTxBuffer[APP_TX_DATA_SIZE];/* Received Data over UART (CDC interface) are stored in this buffer */
uint32_t BuffLength;
uint32_t UserTxBufPtrIn = 0;/* Increment this pointer or roll it back to
                               start address when data are received over USART */
uint32_t UserTxBufPtrOut = 0; /* Increment this pointer or roll it back to
                                 start address when data are sent over USB */ 

两块缓冲区是循环使用，其中的RX、TX是针对USB模块而言，各2K字节。在文件头部还有一个新的数据结构USBD_CDC_LineCodingTypeDef，该结构很简单，如下：

typedef struct
{
  uint32_t bitrate;
  uint8_t  format;
  uint8_t  paritytype;
  uint8_t  datatype;
}USBD_CDC_LineCodingTypeDef;

对应着串口的各个属性，有关LineCoding的相关信息可以在PSTN120文档中找到，如下：

并且罗列了各个属性的取值范围，由此可以看出默认状态下串口属性为：115200波特率、1个停止位，8个数据位，无校验。接着查看CDC类接口的实现函数，首先是硬件资源的初始化操作：

USBD_CDC_ItfTypeDef USBD_CDC_fops = 
{
  CDC_Itf_Init,
  CDC_Itf_DeInit,
  CDC_Itf_Control,
  CDC_Itf_Receive
};

/* Private functions ---------------------------------------------------------*/

/**
  * @brief  CDC_Itf_Init
  *         Initializes the CDC media low layer
  * @param  None
  * @retval Result of the opeartion: USBD_OK if all operations are OK else USBD_FAIL
  */
static int8_t CDC_Itf_Init(void)
{
  /*##-1- Configure the UART peripheral ######################################*/
  /* Put the USART peripheral in the Asynchronous mode (UART Mode) */
  /* USART configured as follows:
      - Word Length = 8 Bits
      - Stop Bit    = One Stop bit
      - Parity      = No parity
      - BaudRate    = 115200 baud
      - Hardware flow control disabled (RTS and CTS signals) */
  UartHandle.Instance        = USARTx;
  UartHandle.Init.BaudRate   = 115200;
  UartHandle.Init.WordLength = UART_WORDLENGTH_8B;
  UartHandle.Init.StopBits   = UART_STOPBITS_1;
  UartHandle.Init.Parity     = UART_PARITY_NONE;
  UartHandle.Init.HwFlowCtl  = UART_HWCONTROL_NONE;
  UartHandle.Init.Mode       = UART_MODE_TX_RX;
  
  if(HAL_UART_Init(&UartHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
  
  /*##-2- Put UART peripheral in IT reception process ########################*/
  /* Any data received will be stored in "UserTxBuffer" buffer  */
  if(HAL_UART_Receive_IT(&UartHandle, (uint8_t *)UserTxBuffer, 1) != HAL_OK)
  {
    /* Transfer error in reception process */
    Error_Handler();
  }
  
  /*##-3- Configure the TIM Base generation  #################################*/
  TIM_Config();
  
  /*##-4- Start the TIM Base generation in interrupt mode ####################*/
  /* Start Channel1 */
  if(HAL_TIM_Base_Start_IT(&TimHandle) != HAL_OK)
  {
    /* Starting Error */
    Error_Handler();
  }
  
  /*##-5- Set Application Buffers ############################################*/
  USBD_CDC_SetTxBuffer(&USBD_Device, UserTxBuffer, 0);
  USBD_CDC_SetRxBuffer(&USBD_Device, UserRxBuffer);
  
  return (USBD_OK);
}

/**
  * @brief  CDC_Itf_DeInit
  *         DeInitializes the CDC media low layer
  * @param  None
  * @retval Result of the opeartion: USBD_OK if all operations are OK else USBD_FAIL
  */
static int8_t CDC_Itf_DeInit(void)
{
  /* DeInitialize the UART peripheral */
  if(HAL_UART_DeInit(&UartHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
  return (USBD_OK);
}

这里主要是串口资源的初始化，按照LineCoding中默认的属性初始化串口资源，并进一步调用之前stm32f1xx_hal_msp.c文件中的HAL_UART_MspInit()，HAL_UART_MspDeInit()方法。此外开启串口接收中断接收字节数据，同时初始化定时器资源，如下：

/**
  * @brief  TIM_Config: Configure TIMx timer
  * @param  None.
  * @retval None.
  */
static void TIM_Config(void)
{  
  /* Set TIMx instance */
  TimHandle.Instance = TIMx;
  
  /* Initialize TIM3 peripheral as follows:
       + Period = 10000 - 1
       + Prescaler = ((SystemCoreClock/2)/10000) - 1
       + ClockDivision = 0
       + Counter direction = Up
  */
  TimHandle.Init.Period = (CDC_POLLING_INTERVAL*1000) - 1;
  TimHandle.Init.Prescaler = 84-1;
  TimHandle.Init.ClockDivision = 0;
  TimHandle.Init.CounterMode = TIM_COUNTERMODE_UP;
  if(HAL_TIM_Base_Init(&TimHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
}

这个没什么说的，在CDC_Itf_Init()函数的末尾有两个设置缓冲区的函数，USBD_CDC_SetTxBuffer()、USBD_CDC_SetRxBuffer()，这两个函数在USB器件库的类文件中，后面再分析，这里知道其作用即可。下面类分析CDC_Itf_Control()函数，该函数管理CDC类请求，如下：

/**
  * @brief  CDC_Itf_Control
  *         Manage the CDC class requests
  * @param  Cmd: Command code            
  * @param  Buf: Buffer containing command data (request parameters)
  * @param  Len: Number of data to be sent (in bytes)
  * @retval Result of the opeartion: USBD_OK if all operations are OK else USBD_FAIL
  */
static int8_t CDC_Itf_Control (uint8_t cmd, uint8_t* pbuf, uint16_t length)
{ 
  switch (cmd)
  {
  case CDC_SEND_ENCAPSULATED_COMMAND:
    /* Add your code here */
    break;

  case CDC_GET_ENCAPSULATED_RESPONSE:
    /* Add your code here */
    break;

  case CDC_SET_COMM_FEATURE:
    /* Add your code here */
    break;

  case CDC_GET_COMM_FEATURE:
    /* Add your code here */
    break;

  case CDC_CLEAR_COMM_FEATURE:
    /* Add your code here */
    break;

  case CDC_SET_LINE_CODING:
    LineCoding.bitrate    = (uint32_t)(pbuf[0] | (pbuf[1] << 8) |\
                            (pbuf[2] << 16) | (pbuf[3] << 24));
    LineCoding.format     = pbuf[4];
    LineCoding.paritytype = pbuf[5];
    LineCoding.datatype   = pbuf[6];
    
    /* Set the new configuration */
    ComPort_Config();
    break;

  case CDC_GET_LINE_CODING:
    pbuf[0] = (uint8_t)(LineCoding.bitrate);
    pbuf[1] = (uint8_t)(LineCoding.bitrate >> 8);
    pbuf[2] = (uint8_t)(LineCoding.bitrate >> 16);
    pbuf[3] = (uint8_t)(LineCoding.bitrate >> 24);
    pbuf[4] = LineCoding.format;
    pbuf[5] = LineCoding.paritytype;
    pbuf[6] = LineCoding.datatype;     
    
    /* Add your code here */
    break;

  case CDC_SET_CONTROL_LINE_STATE:
    /* Add your code here */
    break;

  case CDC_SEND_BREAK:
     /* Add your code here */
    break;    
    
  default:
    break;
  }
  
  return (USBD_OK);
}

USB请求在USB器件库文档中分为三类：标准请求、特定类请求、特定厂商请求。其中标准请求由默认的控制端点0接收处理，另外两类请求由回调函数传递到特定类代码进行处理，这里的CDC_Itf_Control()函数即为回调函数最终实现者，其处理CDC类的特定请求，这些请求可以在PSTN120协议文档以及CDC120协议文档中找到，如下：

在CDC_Itf_Control()可以处理以上请求，但在具体实现上只处理了个别请求，即SET_LINE_CODING和GET_LINE_CODING，代码中各个请求的定义如下：

/*---------------------------------------------------------------------*/
/*  CDC definitions                                                    */
/*---------------------------------------------------------------------*/
#define CDC_SEND_ENCAPSULATED_COMMAND               0x00
#define CDC_GET_ENCAPSULATED_RESPONSE               0x01
#define CDC_SET_COMM_FEATURE                        0x02
#define CDC_GET_COMM_FEATURE                        0x03
#define CDC_CLEAR_COMM_FEATURE                      0x04
#define CDC_SET_LINE_CODING                         0x20
#define CDC_GET_LINE_CODING                         0x21
#define CDC_SET_CONTROL_LINE_STATE                  0x22
#define CDC_SEND_BREAK                              0x23

可以看到各个请求的值与PSTN120协议文档中的值相一致，而CDC_SEND_ENCAPSULATED_COMMAND和CDC_SEND_ENCAPSULATED_RESPONSE的值没有在PSTN120协议文档中，其是在CDC120协议文档中定义的。当我们在PC端上的串口工具中修改串口通信的属性时就会触发CDC_SET_LINE_CODING请求，同时也可以通过CDC_GET_LINE_CODING请求来获取当前串口通信的属性值，在CDC_SET_LINE_CODING请求中通过ComPort_Config()函数类重新配置串口，如下：

/**
  * @brief  ComPort_Config
  *         Configure the COM Port with the parameters received from host.
  * @param  None.
  * @retval None.
  * @note   When a configuration is not supported, a default value is used.
  */
static void ComPort_Config(void)
{
  if(HAL_UART_DeInit(&UartHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
  
  /* set the Stop bit */
  switch (LineCoding.format)
  {
  case 0:
    UartHandle.Init.StopBits = UART_STOPBITS_1;
    break;
  case 2:
    UartHandle.Init.StopBits = UART_STOPBITS_2;
    break;
  default :
    UartHandle.Init.StopBits = UART_STOPBITS_1;
    break;
  }
  
  /* set the parity bit*/
  switch (LineCoding.paritytype)
  {
  case 0:
    UartHandle.Init.Parity = UART_PARITY_NONE;
    break;
  case 1:
    UartHandle.Init.Parity = UART_PARITY_ODD;
    break;
  case 2:
    UartHandle.Init.Parity = UART_PARITY_EVEN;
    break;
  default :
    UartHandle.Init.Parity = UART_PARITY_NONE;
    break;
  }
  
  /*set the data type : only 8bits and 9bits is supported */
  switch (LineCoding.datatype)
  {
  case 0x07:
    /* With this configuration a parity (Even or Odd) must be set */
    UartHandle.Init.WordLength = UART_WORDLENGTH_8B;
    break;
  case 0x08:
    if(UartHandle.Init.Parity == UART_PARITY_NONE)
    {
      UartHandle.Init.WordLength = UART_WORDLENGTH_8B;
    }
    else 
    {
      UartHandle.Init.WordLength = UART_WORDLENGTH_9B;
    }
    
    break;
  default :
    UartHandle.Init.WordLength = UART_WORDLENGTH_8B;
    break;
  }
  
  UartHandle.Init.BaudRate = LineCoding.bitrate;
  UartHandle.Init.HwFlowCtl  = UART_HWCONTROL_NONE;
  UartHandle.Init.Mode       = UART_MODE_TX_RX;
  
  if(HAL_UART_Init(&UartHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }

  /* Start reception: provide the buffer pointer with offset and the buffer size */
  HAL_UART_Receive_IT(&UartHandle, (uint8_t *)(UserTxBuffer + UserTxBufPtrIn), 1);
}

在ComPort_Config()函数的最后再次开启串口接收中断用于接收字节数据，在缓冲区后面追加。SetLineConding和GetLineCoding请求的数据格式如下：

这个要配合SETUP包的结构定义才方便理解，如SetLineCoding请求中bmRequestType值为00100001B对照SETUP包结构可知其为类请求且接收者是接口，wValue为0，wIndex为接口号，wLength为后面数据长度，针对Line Coding结构而言该值为7，wIndex的值在接收者为端点和接口时含义不同，如下：

对于此例而言我们使用的是后者，即低8位标记接口号。接着分析CDC_Itf_Receive()函数，如下：

/**
  * @brief  CDC_Itf_DataRx
  *         Data received over USB OUT endpoint are sent over CDC interface 
  *         through this function.
  * @param  Buf: Buffer of data to be transmitted
  * @param  Len: Number of data received (in bytes)
  * @retval Result of the opeartion: USBD_OK if all operations are OK else USBD_FAIL
  */
static int8_t CDC_Itf_Receive(uint8_t* Buf, uint32_t *Len)
{
  HAL_UART_Transmit_DMA(&UartHandle, Buf, *Len);
  return (USBD_OK);
}

该函数也很简单，将从USB接口收到的数据直接通过串口DMA方式发送出去，至此CDC类接口的回调函数分析完毕，还剩下几个中断回调函数，首先看下串口接收中断回调函数，如下：

/**
  * @brief  Rx Transfer completed callback
  * @param  huart: UART handle
  * @retval None
  */
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
  /* Increment Index for buffer writing */
  UserTxBufPtrIn++;
  
  /* To avoid buffer overflow */
  if(UserTxBufPtrIn == APP_RX_DATA_SIZE)
  {
    UserTxBufPtrIn = 0;
  }
  
  /* Start another reception: provide the buffer pointer with offset and the buffer size */
  HAL_UART_Receive_IT(huart, (uint8_t *)(UserTxBuffer + UserTxBufPtrIn), 1);
}

该回调很简单循环使用USB发送缓冲区，当接收完一个字节后移动USB发送缓冲区下标立即开启下一个字节的接收。接着查看串口发送完成中断回调函数，虽然这里串口发送是使用DMA方式，但在Cube库中会开启三个中断回调函数:半传输完成、传输完成以及错误处理，其中传输完成的回调函数中会进一步调用串口发送完成的回调函数，同时，错误处理的回调函数也会进一步调用串口的错误回调函数，二者如下：

/**
  * @brief  Tx Transfer completed callback
  * @param  huart: UART handle
  * @retval None
  */
void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart)
{
  /* Initiate next USB packet transfer once UART completes transfer (transmitting data over Tx line) */
  USBD_CDC_ReceivePacket(&USBD_Device);
}

/**
  * @brief  UART error callbacks
  * @param  UartHandle: UART handle
  * @retval None
  */
void HAL_UART_ErrorCallback(UART_HandleTypeDef *UartHandle)
{
  /* Transfer error occured in reception and/or transmission process */
  Error_Handler();
}

这里主要看下串口发送完成中断回调函数，其调用USBD_CDC_ReveivePacket()函数来开启下一个USB数据包的接收，该函数在后面再具体分析。现在就只剩下定时器回调函数了，前面已经分析如何把从USB接收到的数据通过串口发送出去，但从串口接收到的数据还没有通过USB发出，定时器的回调函数就是实现该过程的，如下：

/**
  * @brief  TIM period elapsed callback
  * @param  htim: TIM handle
  * @retval None
  */
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
  uint32_t buffptr;
  uint32_t buffsize;
  
  if(UserTxBufPtrOut != UserTxBufPtrIn)
  {
    if(UserTxBufPtrOut > UserTxBufPtrIn) /* rollback */
    {
      buffsize = APP_RX_DATA_SIZE - UserTxBufPtrOut;
    }
    else 
    {
      buffsize = UserTxBufPtrIn - UserTxBufPtrOut;
    }
    
    buffptr = UserTxBufPtrOut;
    
    USBD_CDC_SetTxBuffer(&USBD_Device, (uint8_t*)&UserTxBuffer[buffptr], buffsize);
    
    if(USBD_CDC_TransmitPacket(&USBD_Device) == USBD_OK)
    {
      UserTxBufPtrOut += buffsize;
      if (UserTxBufPtrOut == APP_RX_DATA_SIZE)
      {
        UserTxBufPtrOut = 0;
      }
    }
  }
}

首先是判断UserTxBufPtrOut和UserTxBufPtrIn是否相等以便检测是否在串口中收到了数据，如果不想等则表明在串口中接收到了数据，就要将这些数据通过USB模块发送出去，二者不相等时就需要计算需要通过USB发送的字节数即buffsize的计算，Out比In大时表明缓冲区有循环，则先把末尾数据发送完毕，等下次定时器达到时再从头发送即可。计算完数据量后通过USBD_CDC_SetTxBuffer()函数来设置发送缓冲区及数据大小，通过USBD_CDC_TransmitPacket()函数来开启USB发送，并更新UserTxBufPtrOut数值。至此usbd_cdc_interface文件分析完毕，后面可以开始分析USB器件库了。