ZCM在嵌入式MCU（RTTHREAD）上线程通讯实现

从ZCM通讯简介中我们了解到ZCM还适用于多线程应用，能够提供稳定的内部通讯机制。基于此功能实现了一个内部通讯的demo工程，实现原理：发布订阅使用通一个队列，发布时往队列中写入数据，zcm获取从同一个队列中获取数据，然后按照协议解析，就能拿到一个线程中发布的数据，并根据订阅的主题回调对应的函数执行相应的功能，此demo使用轮询的方式来获取队列中的数据，会性能不足，只是提供一种思路；需要线程中的发布订阅模型还请参考uorb来实现。

实现ZCM的发送接收功能函数

size_t serial_get(uint8_t* data, size_t nData, void* usr)
{
if(recv_send_buf != NULL)
{
return rt_ringbuffer_get(recv_send_buf, data, nData);
}
return 0;
}

size_t serial_put(const uint8_t* data, size_t nData, void* usr)
{
if(recv_send_buf != NULL)
{
return rt_ringbuffer_put(recv_send_buf, data, nData);
}
return 0;
}

2.创建ZCM对象，订阅主题

struct rt_ringbuffer* recv_send_buf = NULL;
zcm_trans_t * serial_trans = NULL;
zcm_t * serial_zcm = NULL;

int main(void)
{
    rt_thread_t tid;
    int count = 1;
    /* set LED0 pin mode to output */
    recv_send_buf = rt_ringbuffer_create(4096);
    if(recv_send_buf == NULL)
    {
        rt_kprintf("recv send buf malloc failed\r\n");
    }
    
    serial_trans = zcm_trans_generic_serial_create(serial_get, serial_put, serial_trans, tick_now, NULL, 1514, 2048);
    serial_zcm = zcm_create_from_trans(serial_trans);
     zcm_subscribe(serial_zcm, "example", example_1_handle, NULL);
    zcm_subscribe(serial_zcm, "example", example_2_handle, NULL);
    zcm_subscribe(serial_zcm, "example", example_3_handle, NULL);
    return RT_EOK;
}

3。创建2个线程，一个线程用数据数据刷新获取订阅的主题执行回调功能，一个用发布主题主题消息到总线中。

int64_t tick_now(void* usr)
{
    return rt_tick_get();
}

void example_1_handle(const zcm_recv_buf_t* rbuf, const char* channel, void* usr)
{
    rt_kprintf("%s, %d, %d\r\n", channel, rbuf->data_size,*((uint32_t *)rbuf->data));
}

void example_2_handle(const zcm_recv_buf_t* rbuf, const char* channel, void* usr)
{
    rt_kprintf("%s, %d, %d\r\n", channel, rbuf->data_size,*((uint32_t *)rbuf->data));
}

void example_3_handle(const zcm_recv_buf_t* rbuf, const char* channel, void* usr)
{
    rt_kprintf("%s, %d, %d\r\n", channel, rbuf->data_size,*((uint32_t *)rbuf->data));
}

void task_entry_1(void* param)
{

    while(1)
    {
        zcm_flush(serial_zcm);
        rt_thread_delay(1);
    }
}

void task_entry_2(void* param)
{
    uint32_t dt = 0;
    while(1)
    {
        dt++;
        zcm_publish(serial_zcm, "example", (uint8_t *)&dt, 1);
        rt_thread_delay(10);
    }
}



int main(void)
{
    rt_thread_t tid;
    int count = 1;
    /* set LED0 pin mode to output */
    recv_send_buf = rt_ringbuffer_create(4096);
    if(recv_send_buf == NULL)
    {
        rt_kprintf("recv send buf malloc failed\r\n");
    }
    
    serial_trans = zcm_trans_generic_serial_create(serial_get, serial_put, serial_trans, tick_now, NULL, 1514, 2048);
    serial_zcm = zcm_create_from_trans(serial_trans);
     zcm_subscribe(serial_zcm, "example", example_1_handle, NULL);
    zcm_subscribe(serial_zcm, "example", example_2_handle, NULL);
    zcm_subscribe(serial_zcm, "example", example_3_handle, NULL);
    tid = rt_thread_create("task_1", task_entry_1, RT_NULL, 1024, 9, 10);
    rt_thread_startup(tid);
    //tid = rt_thread_create("task_2", task_entry_2, RT_NULL, 1024, 10, 10);
    //rt_thread_startup(tid);
    uint32_t dt = 0;
    while(1)
    {
        dt++;
        zcm_publish(serial_zcm, "example", (uint8_t *)&dt, 1);
        rt_kprintf("send :%d\r\n", dt);
        rt_thread_delay(10);
    }
    return RT_EOK;
}

从嵌入式MCU中运行后，我们会发现三个订阅都会被回调（example_1_handle，example_2_handle，example_3_handle），并将接收的打印出来。