RT-Thread基于AT32单片机的485应用开发（二）

在上篇RT-Thread基于AT32单片机的485应用开发（一）中实现了RS485收发，但总觉得效率不高，函数封装也不完善。考虑到RS485总线应用都是主从式结构，比如工业领域常用的Modbus协议，都是以帧为单位进行收发，本次测试对收发函数进行了封装，并对RS485的收发控制引脚根据波特率进行了自动延时控制，降低了CPU负载。

本例中收发全部采用DMA的NON_BLOCKING方式，把接收一帧数据和发送一帧数据进行了函数封装。

测试代码如下：

#include <rtthread.h>
#include <rtdevice.h>

/* 串口设备句柄 */
static rt_device_t serial;

/* 485控制引脚 */
static rt_base_t rs485_ctrl_pin = -1;

/* timeout receive */
static int serial_read_frame(rt_device_t dev, uint8_t *buf, int max_len, uint32_t idle_ms, int timeout_ms)
{
    int rx_len = 0, rc;
    uint32_t idle_time, timeout_time, cur_tick, last_tick;

    timeout_time = rt_tick_from_millisecond(timeout_ms);
    idle_time = rt_tick_from_millisecond(idle_ms);
    cur_tick = rt_tick_get();

    while((rt_tick_get()-last_tick<idle_time && rx_len<max_len) || rx_len<=0){
        rc = rt_device_read(dev, rx_len, buf, max_len-rx_len);
        if(rc>0){
            rx_len += rc;
            last_tick = rt_tick_get();
        }else{
            rt_thread_mdelay(1);
        }
        if(rt_tick_get()-cur_tick>timeout_time && rx_len<=0)
            break;
    }
    return rx_len;
}
/* transmit with auto 485 pin ctrl */
static void serial_write_frame_rs485(rt_device_t dev, uint8_t *buf, int len, int bitrate, int ctrl_pin)
{
    int ms = len * 10 *1000 / bitrate + 2;

    rt_pin_write(rs485_ctrl_pin,1);
    rt_hw_us_delay(10);
    rt_device_write(dev, 0, buf, len);
    rt_thread_mdelay(ms);
    rt_pin_write(rs485_ctrl_pin,0);
}
static void serial_thread_entry(void *parameter)
{
    rt_uint32_t rx_len;
    static unsigned char rx_buf[256];


    while(1){
        rx_len = serial_read_frame(serial, rx_buf, 255, 10, 1000);
        if(rx_len<=0)
            continue;
        serial_write_frame_rs485(serial, rx_buf, rx_len, 115200, rs485_ctrl_pin);
        /* 打印数据 */
        rx_buf[rx_len] = '\0';
        rt_kprintf("rx_len = %d\n",rx_len);
    }
}

static int uart_485_sample(int argc, char *argv[])
{
    rt_err_t ret = RT_EOK;
    char uart_name[RT_NAME_MAX] = "uart4";

    if (argc == 2)
    {
        rt_strncpy(uart_name, argv[1], RT_NAME_MAX);
    }

    rt_kprintf("uart_name = %s\n",uart_name);
    if(rt_strcmp(uart_name,"uart3")==0){
        rs485_ctrl_pin = rt_pin_get("PE.15");
        rt_pin_mode(rs485_ctrl_pin, PIN_MODE_OUTPUT);
        rt_pin_write(rs485_ctrl_pin,0 );
    }else if(rt_strcmp(uart_name,"uart4")==0){
        rs485_ctrl_pin = rt_pin_get("PA.15");
        rt_pin_mode(rs485_ctrl_pin, PIN_MODE_OUTPUT);
        rt_pin_write(rs485_ctrl_pin,0);
    }else{
        return RT_ERROR;
    }

    /* 查找串口设备 */
    serial = rt_device_find(uart_name);
    if (!serial)
    {
        rt_kprintf("find %s failed!\n", uart_name);
        return RT_ERROR;
    }

    /* 以 DMA 接收及轮询发送方式打开串口设备 */
    rt_device_open(serial, RT_DEVICE_FLAG_RX_NON_BLOCKING | RT_DEVICE_FLAG_TX_NON_BLOCKING);

    /* 创建 serial 线程 */
    rt_thread_t thread = rt_thread_create("serial", serial_thread_entry, RT_NULL, 1024, 25, 10);
    /* 创建成功则启动线程 */
    if (thread != RT_NULL)
    {
        rt_thread_startup(thread);
    }
    else
    {
        ret = RT_ERROR;
    }

    return ret;
}
/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(uart_485_sample, uart device rs485 sample);

接收函数，返回收到的字节数：

int serial_read_frame(rt_device_t dev, uint8_t *buf, int max_len, uint32_t idle_ms, int timeout_ms)

idle_ms : 收到最后一个字节数据后空闲的毫秒数

timeout_ms : 如果在这个时间内没有收到数据，则返回0；-1代表一直等待直到收到数据。

发送函数

void serial_write_frame_rs485(rt_device_t dev, uint8_t *buf, int len, int bitrate, int ctrl_pin)

bitrate : 波特率，用于计算实际需要发送的时间

ctrl_pin ：485收发控制引脚号

实际测试结果：