Fanchao Liu wrote:

It can transfer data via DMA,the problem is I don't know when to update hw_ptr and other pointers without interrupt.

Does the hardware have some other means to at least read the current position?

I set a timer and call snd_pcm_period_elapsed() every 50ms but get underrun error.

With a call to snd_pcm_period_elapsed(), the driver guarantees that the current position is at or after the next period boundary.

Regards, Clemens