RT-Thread基于AT32单片机的485应用开发（二）-编程知识

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：