代码收藏家 深入解析STM32 HAL库中的串口中断服务函数
前言
最近在实现利用上位机通过串口发送指令给下位机执行操作的实验，在之前学习串口的过程中我就一直有一个疑惑，那就是为什么在串口中断回调函数内除了要加上自己的操作以外还要在末尾再执行一次接收中断，在查阅了一些资料后我才发现原来和中断服务函数有关
中断服务流程
我们可以从这张图看出串口收发数据的大致流程：
串口收发的寄存器原理
我所使用的F1的串口收发是通过数据寄存器USART_DR来实现的，其内部分为TDR(发送)和RDR(接收)，当向寄存器写入数据时串口会自动发送，当收到数据时会将数据存入该寄存器，对应到HAL库的API如下
HAL_StatusTypeDef HAL_UART_Receive(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)
HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)当我们调用了中断服务入口函数时，向函数传递一个句柄，然后我们就会跳转到真正的中断服务函数，在这里它会判断需要进入的是哪种类型的中断(接收&传输)，具体源代码如下
void HAL_UART_IRQHandler(UART_HandleTypeDef *huart)
{
uint32_t isrflags = READ_REG(huart->Instance->SR);
uint32_t cr1its = READ_REG(huart->Instance->CR1);
uint32_t cr3its = READ_REG(huart->Instance->CR3);
uint32_t errorflags = 0x00U;
uint32_t dmarequest = 0x00U;
/* If no error occurs */
errorflags = (isrflags & (uint32_t)(USART_SR_PE | USART_SR_FE | USART_SR_ORE | USART_SR_NE));
if (errorflags == RESET)
{
/* UART in mode Receiver -------------------------------------------------*/
if (((isrflags & USART_SR_RXNE) != RESET) && ((cr1its & USART_CR1_RXNEIE) != RESET))
{
UART_Receive_IT(huart);
return;
}
}
/* If some errors occur */
if ((errorflags != RESET) && (((cr3its & USART_CR3_EIE) != RESET) || ((cr1its & (USART_CR1_RXNEIE | USART_CR1_PEIE)) != RESET)))
{
/* UART parity error interrupt occurred ----------------------------------*/
if (((isrflags & USART_SR_PE) != RESET) && ((cr1its & USART_CR1_PEIE) != RESET))
{
huart->ErrorCode |= HAL_UART_ERROR_PE;
}
/* UART noise error interrupt occurred -----------------------------------*/
if (((isrflags & USART_SR_NE) != RESET) && ((cr3its & USART_CR3_EIE) != RESET))
{
huart->ErrorCode |= HAL_UART_ERROR_NE;
}
/* UART frame error interrupt occurred -----------------------------------*/
if (((isrflags & USART_SR_FE) != RESET) && ((cr3its & USART_CR3_EIE) != RESET))
{
huart->ErrorCode |= HAL_UART_ERROR_FE;
}
/* UART Over-Run interrupt occurred --------------------------------------*/
if (((isrflags & USART_SR_ORE) != RESET) && (((cr1its & USART_CR1_RXNEIE) != RESET) || ((cr3its & USART_CR3_EIE) != RESET)))
{
huart->ErrorCode |= HAL_UART_ERROR_ORE;
}
/* Call UART Error Call back function if need be --------------------------*/
if (huart->ErrorCode != HAL_UART_ERROR_NONE)
{
/* UART in mode Receiver -----------------------------------------------*/
if (((isrflags & USART_SR_RXNE) != RESET) && ((cr1its & USART_CR1_RXNEIE) != RESET))
{
UART_Receive_IT(huart);
}
/* If Overrun error occurs, or if any error occurs in DMA mode reception,
consider error as blocking */
dmarequest = HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR);
if (((huart->ErrorCode & HAL_UART_ERROR_ORE) != RESET) || dmarequest)
{
/* Blocking error : transfer is aborted
Set the UART state ready to be able to start again the process,
Disable Rx Interrupts, and disable Rx DMA request, if ongoing */
UART_EndRxTransfer(huart);
/* Disable the UART DMA Rx request if enabled */
if (HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR))
{
CLEAR_BIT(huart->Instance->CR3, USART_CR3_DMAR);
/* Abort the UART DMA Rx channel */
if (huart->hdmarx != NULL)
{
/* Set the UART DMA Abort callback :
will lead to call HAL_UART_ErrorCallback() at end of DMA abort procedure */
huart->hdmarx->XferAbortCallback = UART_DMAAbortOnError;
if (HAL_DMA_Abort_IT(huart->hdmarx) != HAL_OK)
{
/* Call Directly XferAbortCallback function in case of error */
huart->hdmarx->XferAbortCallback(huart->hdmarx);
}
}
else
{
/* Call user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered error callback*/
huart->ErrorCallback(huart);
#else
/*Call legacy weak error callback*/
HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
}
}
else
{
/* Call user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered error callback*/
huart->ErrorCallback(huart);
#else
/*Call legacy weak error callback*/
HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
}
}
else
{
/* Non Blocking error : transfer could go on.
Error is notified to user through user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered error callback*/
huart->ErrorCallback(huart);
#else
/*Call legacy weak error callback*/
HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
huart->ErrorCode = HAL_UART_ERROR_NONE;
}
}
return;
} /* End if some error occurs */
/* Check current reception Mode :
If Reception till IDLE event has been selected : */
if ( (huart->ReceptionType == HAL_UART_RECEPTION_TOIDLE)
&&((isrflags & USART_SR_IDLE) != 0U)
&&((cr1its & USART_SR_IDLE) != 0U))
{
__HAL_UART_CLEAR_IDLEFLAG(huart);
/* Check if DMA mode is enabled in UART */
if (HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR))
{
/* DMA mode enabled */
/* Check received length : If all expected data are received, do nothing,
(DMA cplt callback will be called).
Otherwise, if at least one data has already been received, IDLE event is to be notified to user */
uint16_t nb_remaining_rx_data = (uint16_t) __HAL_DMA_GET_COUNTER(huart->hdmarx);
if ( (nb_remaining_rx_data > 0U)
&&(nb_remaining_rx_data < huart->RxXferSize))
{
/* Reception is not complete */
huart->RxXferCount = nb_remaining_rx_data;
/* In Normal mode, end DMA xfer and HAL UART Rx process*/
if (huart->hdmarx->Init.Mode != DMA_CIRCULAR)
{
/* Disable PE and ERR (Frame error, noise error, overrun error) interrupts */
CLEAR_BIT(huart->Instance->CR1, USART_CR1_PEIE);
CLEAR_BIT(huart->Instance->CR3, USART_CR3_EIE);
/* Disable the DMA transfer for the receiver request by resetting the DMAR bit
in the UART CR3 register */
CLEAR_BIT(huart->Instance->CR3, USART_CR3_DMAR);
/* At end of Rx process, restore huart->RxState to Ready */
huart->RxState = HAL_UART_STATE_READY;
huart->ReceptionType = HAL_UART_RECEPTION_STANDARD;
CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);
/* Last bytes received, so no need as the abort is immediate */
(void)HAL_DMA_Abort(huart->hdmarx);
}
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered Rx Event callback*/
huart->RxEventCallback(huart, (huart->RxXferSize - huart->RxXferCount));
#else
/*Call legacy weak Rx Event callback*/
HAL_UARTEx_RxEventCallback(huart, (huart->RxXferSize - huart->RxXferCount));
#endif
}
return;
}
else
{
/* DMA mode not enabled */
/* Check received length : If all expected data are received, do nothing.
Otherwise, if at least one data has already been received, IDLE event is to be notified to user */
uint16_t nb_rx_data = huart->RxXferSize - huart->RxXferCount;
if ( (huart->RxXferCount > 0U)
&&(nb_rx_data > 0U) )
{
/* Disable the UART Parity Error Interrupt and RXNE interrupts */
CLEAR_BIT(huart->Instance->CR1, (USART_CR1_RXNEIE | USART_CR1_PEIE));
/* Disable the UART Error Interrupt: (Frame error, noise error, overrun error) */
CLEAR_BIT(huart->Instance->CR3, USART_CR3_EIE);
/* Rx process is completed, restore huart->RxState to Ready */
huart->RxState = HAL_UART_STATE_READY;
huart->ReceptionType = HAL_UART_RECEPTION_STANDARD;
CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered Rx complete callback*/
huart->RxEventCallback(huart, nb_rx_data);
#else
/*Call legacy weak Rx Event callback*/
HAL_UARTEx_RxEventCallback(huart, nb_rx_data);
#endif
}
return;
}
}
/* UART in mode Transmitter ------------------------------------------------*/
if (((isrflags & USART_SR_TXE) != RESET) && ((cr1its & USART_CR1_TXEIE) != RESET))
{
UART_Transmit_IT(huart);
return;
}
/* UART in mode Transmitter end --------------------------------------------*/
if (((isrflags & USART_SR_TC) != RESET) && ((cr1its & USART_CR1_TCIE) != RESET))
{
UART_EndTransmit_IT(huart);
return;
}
}我们只需要挑关键的地方来看：在代码的最开头定义了几个标志位，用于判断是否为接收类型的中断，如果是的话则调用接收中断函数，代码如下
static HAL_StatusTypeDef UART_Receive_IT(UART_HandleTypeDef *huart)
{
uint8_t *pdata8bits;
uint16_t *pdata16bits;
/* Check that a Rx process is ongoing */
if (huart->RxState == HAL_UART_STATE_BUSY_RX)
{
if ((huart->Init.WordLength == UART_WORDLENGTH_9B) && (huart->Init.Parity == UART_PARITY_NONE))
{
pdata8bits = NULL;
pdata16bits = (uint16_t *) huart->pRxBuffPtr;
*pdata16bits = (uint16_t)(huart->Instance->DR & (uint16_t)0x01FF);
huart->pRxBuffPtr += 2U;
}
else
{
pdata8bits = (uint8_t *) huart->pRxBuffPtr;
pdata16bits = NULL;
if ((huart->Init.WordLength == UART_WORDLENGTH_9B) || ((huart->Init.WordLength == UART_WORDLENGTH_8B) && (huart->Init.Parity == UART_PARITY_NONE)))
{
*pdata8bits = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);
}
else
{
*pdata8bits = (uint8_t)(huart->Instance->DR & (uint8_t)0x007F);
}
huart->pRxBuffPtr += 1U;
}
if (--huart->RxXferCount == 0U)
{
/* Disable the UART Data Register not empty Interrupt */
__HAL_UART_DISABLE_IT(huart, UART_IT_RXNE);
/* Disable the UART Parity Error Interrupt */
__HAL_UART_DISABLE_IT(huart, UART_IT_PE);
/* Disable the UART Error Interrupt: (Frame error, noise error, overrun error) */
__HAL_UART_DISABLE_IT(huart, UART_IT_ERR);
/* Rx process is completed, restore huart->RxState to Ready */
huart->RxState = HAL_UART_STATE_READY;
/* Check current reception Mode :
If Reception till IDLE event has been selected : */
if (huart->ReceptionType == HAL_UART_RECEPTION_TOIDLE)
{
/* Set reception type to Standard */
huart->ReceptionType = HAL_UART_RECEPTION_STANDARD;
/* Disable IDLE interrupt */
CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);
/* Check if IDLE flag is set */
if (__HAL_UART_GET_FLAG(huart, UART_FLAG_IDLE))
{
/* Clear IDLE flag in ISR */
__HAL_UART_CLEAR_IDLEFLAG(huart);
}
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered Rx Event callback*/
huart->RxEventCallback(huart, huart->RxXferSize);
#else
/*Call legacy weak Rx Event callback*/
HAL_UARTEx_RxEventCallback(huart, huart->RxXferSize);
#endif
}
else
{
/* Standard reception API called */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
/*Call registered Rx complete callback*/
huart->RxCpltCallback(huart);
#else
/*Call legacy weak Rx complete callback*/
HAL_UART_RxCpltCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
}
return HAL_OK;
}
return HAL_OK;
}
else
{
return HAL_BUSY;
}
}
可以看到这个函数的作用是将每次中断接收到的字符保存在串口的缓存指针中，同时计数器变量自减1，当计数器为0时调用回调函数实现用户处理逻辑
串口句柄具体定义如下
typedef struct __UART_HandleTypeDef
{
USART_TypeDef *Instance; /*!< UART registers base address */
UART_InitTypeDef Init; /*!< UART communication parameters */
uint8_t *pTxBuffPtr; /*!< Pointer to UART Tx transfer Buffer */
uint16_t TxXferSize; /*!< UART Tx Transfer size */
__IO uint16_t TxXferCount; /*!< UART Tx Transfer Counter */
uint8_t *pRxBuffPtr; /*!< Pointer to UART Rx transfer Buffer */
uint16_t RxXferSize; /*!< UART Rx Transfer size */
__IO uint16_t RxXferCount; /*!< UART Rx Transfer Counter */
__IO HAL_UART_RxTypeTypeDef ReceptionType; /*!< Type of ongoing reception */
DMA_HandleTypeDef *hdmatx; /*!< UART Tx DMA Handle parameters */
DMA_HandleTypeDef *hdmarx; /*!< UART Rx DMA Handle parameters */
HAL_LockTypeDef Lock; /*!< Locking object */
__IO HAL_UART_StateTypeDef gState; /*!< UART state information related to global Handle management
and also related to Tx operations.
This parameter can be a value of @ref HAL_UART_StateTypeDef */
__IO HAL_UART_StateTypeDef RxState; /*!< UART state information related to Rx operations.
This parameter can be a value of @ref HAL_UART_StateTypeDef */
__IO uint32_t ErrorCode; /*!< UART Error code */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
void (* TxHalfCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Tx Half Complete Callback */
void (* TxCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Tx Complete Callback */
void (* RxHalfCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Rx Half Complete Callback */
void (* RxCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Rx Complete Callback */
void (* ErrorCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Error Callback */
void (* AbortCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Abort Complete Callback */
void (* AbortTransmitCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Abort Transmit Complete Callback */
void (* AbortReceiveCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Abort Receive Complete Callback */
void (* WakeupCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Wakeup Callback */
void (* RxEventCallback)(struct __UART_HandleTypeDef *huart, uint16_t Pos); /*!< UART Reception Event Callback */
void (* MspInitCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Msp Init callback */
void (* MspDeInitCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Msp DeInit callback */
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
} UART_HandleTypeDef;
因此现在我们可以大致明白为何在回调函数内还需要再进一次中断了：当我们在回调函数中调用
HAL_UART_Receive_IT
其会跳转到
UART_Start_Receive_IT
更新串口句柄中的具体内容，我们缓冲区的数据量也是在这个时候被传入的
而当有数据传输来的时候，在函数内部就会对SR寄存器的位进行赋值
此时会产生硬件中断，进入中断服务函数，在服务函数内部其会通过前面已经写下的标志位判断到底是要接收还是发送，而只有当真正有数据接收到时接收数据标志位才会被赋值，因此在没有接收到数据时是不会进入中断的，直到接收到数据，然而如果我们不写这一条语句的话，那么即使我们向串口发送数据，中断服务函数也不会启动，因为此时只有接收数据位被赋值。
补充
这里我再补充一下，当我们调用串口接收中断函数时，有可能会产生发送数据过长导致终端阻塞的问题，因此我们需要设置一个标志位重新进入中断
当中断阻塞时，timeout就会被置为1，此时循环中的判断就会重新再进入一次中断并清除标志位直至数据全部收完
