串口驱动编程实现

samsung.c:

/* linux/drivers/serial/samsuing.c


/* ? - where has parity gone?? */
#define S3C2410_UERSTAT_PARITY (0x1000)

static irqreturn_t
s3c24xx_serial_rx_chars(int irq, void *dev_id)
{
    struct s3c24xx_uart_port *ourport = dev_id;
    struct uart_port *port = &ourport->port;
    struct tty_struct *tty = port->info->port.tty;
    unsigned int ufcon, ch, flag, ufstat, uerstat;
    int max_count = 64;

    while(max_count-- > 0)
    {
     //1.如果接收FIFO为空
        ufstat = rd_regl(port, S3C2410_UFSTAT);
     if((ufstat & 0x3f) == 0)
            break;
     //2.
        uerstat = rd_regl(port, S3C2410_UERSTAT);
     //3.从URXH寄存器中获取接收到的字符
        ch = rd_regb(port, S3C2410_URXH);
     //6.
     if(uart_handle_sysrq_char(port, ch))
            break;
        flag = TTY_NORMAL;
     //7.
        uart_insert_char(port, uerstat, S3C2410_UERSTAT_OVERRUN, ch, flag);
    }
    //8.
    tty_flip_buffer_push(tty);

    return IRQ_HANDLED;
}

static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
{
    struct s3c24xx_uart_port *ourport = id;
    struct uart_port *port = &ourport->port;
    struct circ_buf *xmit = &port->info->xmit;
    int count = 256;

    //1.判断x_char是否为0
    if(port->x_char)
    {
        wr_regb(port, S3C2410_UTXH, port->x_char);
        goto out;
    }

    //2.如果发送缓冲空，或者驱动为停止发送状态，则取消发送
    if(uart_circ_empty(xmit) || uart_tx_stopped(port))
    {
        s3c24xx_serial_stop_tx(port);
        goto out;
    }

    //3.循环发送，循环条件：发送缓冲不为空
    while(!uart_circ_empty(xmit) && ((count--)>0))
    {
     //3.1 判断FIFO是否满了
     if(rd_regl(port, S3C2410_UFSTAT) & (1<<14))
            break;
     //3.2 将要发送的字符写入发送寄存器
        wr_regl(port, S3C2410_UTXH, xmit->buf[xmit->tail]);
     //3.3 修改循环缓冲的尾部位置
        xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE -1);
        port->icount.tx++;
    }
    //4.如果发送余量数据<256，唤醒之前阻塞的发送进程
    if(uart_circ_chars_pending(xmit) < 256)
    {
        uart_write_wakeup(port);
    }
    //5.如果发送缓冲空，关闭发送功能
    if(uart_circ_empty(xmit))
        s3c24xx_serial_stop_tx(port);
out:
    return IRQ_HANDLED;
}