STM32 -USART中断方式

前面我们接收了串口通信的查询方式，现在我们来介绍中断方式。

步骤一：初始化GPIO
GPIO_InitTypeDef GPIO_InitStructure;
/* Configure USART1 Tx (PA.09) as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* Configure USART1 Rx (PA.10) as input floating */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);

步骤二：开时钟
/* Enable USART1, GPIOA, GPIOD and AFIO clocks */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOD
| RCC_APB2Periph_AFIO, ENABLE);
在此说明，不用设置RCC_APB2Periph_AFIO也是可以的，也就是在此没有使用复用功能。
这两个步骤与查询方式是一样的。

步骤三：初始化USART1
USART_InitStructure.USART_BaudRate = 115200;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_2;
USART_InitStructure.USART_Parity = USART_Parity_No; //设置奇校验时，通信出现错误
USART_InitStructure.USART_HardwareFlowControl=USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
/* Configure the USART1 */
USART_Init(USART1, &USART_InitStructure);
/* Enable the USART Transmoit interrupt: this interrupt is generated when the
USART1 transmit data register is empty */
USART_ITConfig(USART1, USART_IT_TXE, ENABLE);
/* Enable the USART Receive interrupt: this interrupt is generated when the
USART1 receive data register is not empty */
USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
/* Enable USART1 */
USART_Cmd(USART1, ENABLE);
在这里要使能USART1的外设中断，如USART_ITConfig(USART1, USART_IT_TXE, ENABLE);这就是使能发送中断，但发送寄存器空时能产生中断。

步骤四：编写中断函数
uint8_t TxBuffer[] = "/n/rUSART Hyperterminal Interrupts Example: USART-Hyperterminal/
communication using Interrupt/n/r";
uint8_t RxBuffer[RxBufferSize];
uint8_t NbrOfDataToTransfer = TxBufferSize;
uint8_t NbrOfDataToRead = RxBufferSize;
uint8_t TxCounter = 0;
uint16_t RxCounter = 0;

void USART1_IRQHandler(void)
{
if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
{
/* Read one byte from the receive data register */
RxBuffer[RxCounter++] = (USART_ReceiveData(USART1) & 0x7F);
if(RxCounter == NbrOfDataToRead)
{
/* Disable the USART Receive interrupt */
USART_ITConfig(USART1, USART_IT_RXNE, DISABLE);
}
}

if(USART_GetITStatus(USART1, USART_IT_TXE) != RESET)
{
/* Write one byte to the transmit data register */
USART_SendData(USART1, TxBuffer[TxCounter++]);
if(TxCounter == NbrOfDataToTransfer)
{
/* Disable the USART1 Transmit interrupt */
USART_ITConfig(USART1, USART_IT_TXE, DISABLE);
}
}
}

至此程序就结束了。

我们就会有个疑问,main()只包括前三个步骤的初始化和一个死循环，那么中断又是如何触发的呢，main（）的结构如下：
int main(void)
{
/* System Clocks Configuration */
RCC_Configuration();
/* NVIC configuration */
NVIC_Configuration();
/* Configure the GPIO ports */
GPIO_Configuration();
USART_Configuration();

while (1)
{
}
}
原来是这样的：状态寄存器USART_SR的复位值为0x00C0H, 也就是第七位TXE和第六位TC复位值为1，而TXE=1,表明发送数据寄存器为空， TC=1表明发送已完成。而在USART的设置中有
USART_ITConfig(USART1, USART_IT_TXE, ENABLE);
USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
这两句使能中断，也就是说当TXE=1就会进入中断，所以程序初始化后就能进入中断，执行
if(USART_GetITStatus(USART1, USART_IT_TXE) != RESET)
{
/* Write one byte to the transmit data register */
USART_SendData(USART1, TxBuffer[TxCounter++]);
if(TxCounter == NbrOfDataToTransfer)
{
/* Disable the USART1 Transmit interrupt */
USART_ITConfig(USART1, USART_IT_TXE, DISABLE);
}
}