编写一份RTTHREAD的MODBUS RTU驱动程序

以下是一个简单的RTTHREAD的MODBUS RTU驱动程序示例，该程序使用串口通信协议进行通信：

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

#define MODBUS_SLAVE_ADDRESS    1
#define MODBUS_FUNCTION_CODE    3
#define MODBUS_START_ADDRESS    0
#define MODBUS_NUM_REGISTERS    10

static rt_device_t modbus_dev;

static int modbus_read_registers(rt_uint8_t slave_addr, rt_uint8_t func_code, rt_uint16_t start_addr, rt_uint16_t num_regs, rt_uint16_t *regs)
{
    rt_uint8_t request[8];
    rt_uint8_t response[5 + 2 * num_regs];
    rt_uint16_t crc;
    rt_uint16_t i;
    rt_size_t size;

    /* Construct request message */
    request[0] = slave_addr;
    request[1] = func_code;
    request[2] = (start_addr >> 8) & 0xff;
    request[3] = start_addr & 0xff;
    request[4] = (num_regs >> 8) & 0xff;
    request[5] = num_regs & 0xff;

    /* Calculate CRC */
    crc = rt_modbus_crc(request, 6);
    request[6] = crc & 0xff;
    request[7] = (crc >> 8) & 0xff;

    /* Send request message */
    size = rt_device_write(modbus_dev, 0, request, sizeof(request));
    if (size != sizeof(request))
    {
        rt_kprintf("MODBUS RTU: Failed to send request message!\n");
        return -RT_ERROR;
    }

    /* Receive response message */
    size = rt_device_read(modbus_dev, 0, response, sizeof(response));
    if (size != sizeof(response))
    {
        rt_kprintf("MODBUS RTU: Failed to receive response message!\n");
        return -RT_ERROR;
    }

    /* Check response message */
    if (response[0] != slave_addr || response[1] != func_code || response[2] != 2 * num_regs)
    {
        rt_kprintf("MODBUS RTU: Invalid response message!\n");
        return -RT_ERROR;
    }

    /* Extract data from response message */
    for (i = 0; i < num_regs; ++i)
    {
        regs[i] = (response[3 + 2 * i] << 8) | response[4 + 2 * i];
    }

    return RT_EOK;
}

static void modbus_thread_entry(void *parameter)
{
    rt_uint16_t regs[MODBUS_NUM_REGISTERS];

    while (1)
    {
        /* Read registers from MODBUS slave device */
        if (modbus_read_registers(MODBUS_SLAVE_ADDRESS, MODBUS_FUNCTION_CODE, MODBUS_START_ADDRESS, MODBUS_NUM_REGISTERS, regs) == RT_EOK)
        {
            /* Process the received data */
            // ...
        }

        /* Wait for next polling interval */
        rt_thread_mdelay(1000);
    }
}

int modbus_init(void)
{
    /* Open MODBUS RTU device */
    modbus_dev = rt_device_find("uart1");
    if (modbus_dev == RT_NULL)
    {
        rt_kprintf("MODBUS RTU: Failed to open device!\n");
        return -RT_ERROR;
    }
    if (rt_device_open(modbus_dev, RT_DEVICE_OFLAG_RDWR) != RT_EOK)
    {
        rt_kprintf("MODBUS RTU: Failed to open device!\n");
        return -RT_ERROR;
    }

    /* Create MODBUS RTU polling thread */
    rt_thread_t tid = rt_thread_create("modbus", modbus_thread_entry, RT_NULL, 1024, 25, 5);
    if (tid != RT_NULL)
    {
        rt_thread_startup(tid);
        return RT_EOK;
    }
    else
    {
        rt_kprintf("MODBUS RTU: Failed to create thread!\n");
        return -RT_ERROR;
    }
}

该程序包含一个 `modbus_read_registers()` 函数，该函数可以向MODBUS从设备发送读取寄存器请求，并接收从设备返回的数据。在主线程中，我们可以通过调用该函数来获取MODBUS从设备的寄存器值，并对其进行处理。

该程序还包含一个 `modbus_init()` 函数，该函数打开MODBUS RTU设备并创建一个MODBUS RTU轮询线程。在主程序中，我们可以通过调用该函数来启动MODBUS RTU驱动程序。