SDMMC驱动的mmc_detect疑惑

发布于 2020-11-10 22:24:14 浏览：1501 订阅该版

```C
void mmcsd_detect(void *param)
{
    struct rt_mmcsd_host *host;
    rt_uint32_t  ocr;
    rt_int32_t  err;

while (1) 
    {
        if (rt_mb_recv(&mmcsd_detect_mb, (rt_ubase_t *)&host, RT_WAITING_FOREVER) == RT_EOK)	//这句是做什么用的？
        {
            if (host->card == RT_NULL)
            {
                mmcsd_host_lock(host);
                mmcsd_power_up(host);
                mmcsd_go_idle(host);

mmcsd_send_if_cond(host, host->valid_ocr);

err = sdio_io_send_op_cond(host, 0, &ocr);
                if (!err)
                {
                    if (init_sdio(host, ocr))
                        mmcsd_power_off(host);
                    mmcsd_host_unlock(host);
                    continue;
                }

/*
                 * detect SD card
                 */
                err = mmcsd_send_app_op_cond(host, 0, &ocr);
                if (!err) 
                {
                    if (init_sd(host, ocr))
                        mmcsd_power_off(host);
                    mmcsd_host_unlock(host);
                    rt_mb_send(&mmcsd_hotpluge_mb, (rt_uint32_t)host);
                    continue;
                }
                
                /*
                 * detect mmc card
                 */
                err = mmc_send_op_cond(host, 0, &ocr);
                if (!err) 
                {
                    if (init_mmc(host, ocr))
                        mmcsd_power_off(host);
                    mmcsd_host_unlock(host);
                    rt_mb_send(&mmcsd_hotpluge_mb, (rt_uint32_t)host);
                    continue;
                }
                mmcsd_host_unlock(host);
            }
            else
            {
            	/* card removed */
            	mmcsd_host_lock(host);
            	if (host->card->sdio_function_num != 0)
            	{
            		LOG_W("unsupport sdio card plug out!");
            	}
            	else
            	{
            		rt_mmcsd_blk_remove(host->card);
            		rt_free(host->card);

host->card = RT_NULL;
            	}
            	mmcsd_host_unlock(host);
            	rt_mb_send(&mmcsd_hotpluge_mb, (rt_uint32_t)host);
            }
        }
    }
}

int rt_mmcsd_core_init(void)
{
    rt_err_t ret;

/* initialize detect SD cart thread */
    /* initialize mailbox and create detect SD card thread */
    ret = rt_mb_init(&mmcsd_detect_mb, "mmcsdmb",
        &mmcsd_detect_mb_pool[0], sizeof(mmcsd_detect_mb_pool) / sizeof(mmcsd_detect_mb_pool[0]),
        RT_IPC_FLAG_FIFO);
    RT_ASSERT(ret == RT_EOK);

ret = rt_mb_init(&mmcsd_hotpluge_mb, "mmcsdhotplugmb",
        &mmcsd_hotpluge_mb_pool[0], sizeof(mmcsd_hotpluge_mb_pool) / sizeof(mmcsd_hotpluge_mb_pool[0]),
        RT_IPC_FLAG_FIFO);
    RT_ASSERT(ret == RT_EOK);
     ret = rt_thread_init(&mmcsd_detect_thread, "mmcsd_detect", mmcsd_detect, RT_NULL, 
                 &mmcsd_stack[0], RT_MMCSD_STACK_SIZE, RT_MMCSD_THREAD_PREORITY, 20);
    if (ret == RT_EOK) 
    {
        rt_thread_startup(&mmcsd_detect_thread);
    }

rt_sdio_init();

return 0;
}
INIT_PREV_EXPORT(rt_mmcsd_core_init);
```

问题：if (rt_mb_recv(&mmcsd_detect_mb, (rt_ubase_t *)&host, RT_WAITING_FOREVER) == RT_EOK)	//这句是做什么用的？运行起来if语句内条件不为真，这是为什么。