通过 8051 微控制器上的中断进行 UART 传输

Question

我的平台是 c8051F120 微控制器。我想使用中断通过 UART0 发送（=tx）字节。到目前为止，我的设计如下：

#define UART0_TX_SIZE 16    
char UART0_tx[UART0_TX_SIZE];
short UART0_tx_uart = 0;
short UART0_tx_main = 0;
short UART0_tx_available = 0;

void UART0_putChar(char value) {
  char SAVE_SFRPAGE;
  bit EA_SAVE = EA;
  // potentially blocking code
  while (UART0_tx_available == UART0_TX_SIZE)
    ;
  // disable interrupts
  EA = 0;
  EA = 0;
  if (UART0_tx_available) {
    UART0_tx[UART0_tx_main] = value;
    ++UART0_tx_main;
    if (UART0_tx_main == UART0_TX_SIZE)
      UART0_tx_main = 0;
    ++UART0_tx_available;
  } else {
    SAVE_SFRPAGE = SFRPAGE;
    SFRPAGE = UART0_PAGE;
    SBUF0 = value;
    SFRPAGE = SAVE_SFRPAGE;
  }
  // reenable if necessary
  EA = EA_SAVE;
}

// (return void works for other interrupts)
void UART0_Interrupt() interrupt (4) {
  if (RI0 == 1) {
    RI0 = 0;
  }
  if (TI0 == 1) { // cause of interrupt: previous tx is finished
    TI0 = 0; // Q: Should this clear tx interrupt flag be further down?
    if (SSTA0 & 0x20) { // Errors tx collision
      SSTA0 &= 0xDF;
    }
    if (UART0_tx_available) { // If buffer not empty
      --UART0_tx_available; // Decrease array size
      SBUF0 = UART0_tx[UART0_tx_uart]; //Transmit
      ++UART0_tx_uart; //Update counter
      if (UART0_tx_uart == UART0_TX_SIZE)
        UART0_tx_uart = 0;
    }    
  }
}

我很确定通过 Timer2（不是上述代码的一部分）对 UART0 寄存器和计时进行的初始化是正确的，因为我可以使用阻塞功能：

char putchar_Blocking(char value) {
  char SFRPAGE_SAVE = SFRPAGE;
  SFRPAGE = UART0_PAGE;
  while (!TI0) // while TI0 == 1 wait for transmit complete
    ;
  TI0 = 0;
  SBUF0 = value;
  SFRPAGE = SFRPAGE_SAVE;
  return value;
}

当我要切换到中断设计的时候，当然我也设置了

ES0 = 1;

有人在我的设计中发现了试图使用中断的缺陷吗？或者，有人有这方面的示例代码吗？谢谢！非常感谢 jszakmeister，他回答了我关于读取 TCNT 寄存器的问题。

Answer 1

我看到的最大缺陷是你不应该有任何变量（例如：UART0_tx_available）被主代码和中断代码修改。

通常我使用一个循环缓冲区和两个指针来实现一个中断驱动的 UART。

这是 AVR micro 的简单 C 示例。我的 8051 代码都是汇编代码。

/* size of RX/TX buffers */
#define UART_RX_BUFFER_SIZE  16
#define UART_TX_BUFFER_SIZE  16
#define UART_RX_BUFFER_MASK ( UART_RX_BUFFER_SIZE - 1)
#define UART_TX_BUFFER_MASK ( UART_TX_BUFFER_SIZE - 1)

#if ( UART_RX_BUFFER_SIZE & UART_RX_BUFFER_MASK )
#error RX buffer size is not a power of 2   
#endif  
#if ( UART_TX_BUFFER_SIZE & UART_TX_BUFFER_MASK )
#error TX buffer size is not a power of 2
#endif

/* 
 *  module global variables
 */
static volatile unsigned char UART_TxBuf[UART_TX_BUFFER_SIZE];
static volatile unsigned char UART_RxBuf[UART_RX_BUFFER_SIZE];
static volatile unsigned char UART_TxHead;
static volatile unsigned char UART_TxTail;
static volatile unsigned char UART_RxHead;
static volatile unsigned char UART_RxTail;
static volatile unsigned char UART_LastRxError;

SIGNAL(UART0_TRANSMIT_INTERRUPT)
/*************************************************************************
Function: UART Data Register Empty interrupt
Purpose:  called when the UART is ready to transmit the next byte
**************************************************************************/
{
    unsigned char tmptail;

    if ( UART_TxHead != UART_TxTail) {
        /* calculate and store new buffer index */
        tmptail = (UART_TxTail + 1) & UART_TX_BUFFER_MASK;

        /* get one byte from buffer and write it to UART */
        UART0_DATA = UART_TxBuf[tmptail];  /* start transmission */
        UART_TxTail = tmptail;
    }else{
        /* tx buffer empty, disable UDRE interrupt */
        UART0_CONTROL &= ~_BV(UART0_UDRIE);
    }
}

/*************************************************************************
Function: uart_putc()
Purpose:  write byte to ringbuffer for transmitting via UART
Input:    byte to be transmitted
Returns:  none
**************************************************************************/
void uart_putc(unsigned char data)
{
    unsigned char tmphead;

    tmphead  = (UART_TxHead + 1) & UART_TX_BUFFER_MASK;

    while ( tmphead == UART_TxTail ){
        ;/* wait for free space in buffer */
    }

    UART_TxBuf[tmphead] = data;
    UART_TxHead = tmphead;

    /* enable UDRE interrupt */
    UART0_CONTROL |= _BV(UART0_UDRIE);

}/* uart_putc */

特别感谢 Peter Fleury http://jump.to/fleury 提供这些例程来自的库。

Answer 2

我的同事郭雄发现了错误：变量UART0_tx_available没有在正确的地方增加和减少。以下是经过修正和测试的版本：

#define UART0_TX_SIZE 16    
char UART0_tx[UART0_TX_SIZE];
short UART0_tx_uart = 0;
short UART0_tx_main = 0;
short UART0_tx_available = 0;

void UART0_putChar(char value) {
  char SAVE_SFRPAGE;
  bit EA_SAVE = EA;
  // potentially blocking code
  while (UART0_tx_available == UART0_TX_SIZE)
    ;
  // disable interrupts
  EA = 0;
  EA = 0;
  if (UART0_tx_available) {
    UART0_tx[UART0_tx_main] = value;
    ++UART0_tx_main;
    if (UART0_tx_main == UART0_TX_SIZE)
      UART0_tx_main = 0;
  } else {
    SAVE_SFRPAGE = SFRPAGE;
    SFRPAGE = UART0_PAGE;
    SBUF0 = value;
    SFRPAGE = SAVE_SFRPAGE;
  }
  ++UART0_tx_available;
  // reenable if necessary
  EA = EA_SAVE;
}

// (return void works for other interrupts)
void UART0_Interrupt() interrupt (4) {
  if (RI0 == 1) {
    RI0 = 0;
  }
  if (TI0 == 1) { // cause of interrupt: previous tx is finished
    TI0 = 0; // Q: Should this clear tx interrupt flag be further down?
    if (SSTA0 & 0x20) { // Errors tx collision
      SSTA0 &= 0xDF;
    }
    --UART0_tx_available; // Decrease array size
    if (UART0_tx_available) { // If buffer not empty
      SBUF0 = UART0_tx[UART0_tx_uart]; //Transmit
      ++UART0_tx_uart; //Update counter
      if (UART0_tx_uart == UART0_TX_SIZE)
        UART0_tx_uart = 0;
    }    
  }
}