Hi,

I'm currently developing an ALSA ioplug plugin that should transfer audio samples to a DSP over UART.

In my plugin code I set up the hardware constrains (HW_PERIOD_BYTES and HW_PERIODS being among them) and then I utilize the transfer callback to send the audio chunk over UART.

The DSP application would like to have exactly 156 - 164 audio samples at a time, where the sampling rate has to be 8 kHz and the format is S16_LE. In between there has to be a delay of 20ms (which is equal to 164 audio frames at a sampling rate of 8 kHz (i.e. 164 * 125us = 20,5 ms).

For this reason I configured HW_PERIOD_BYTES with these values. The result is that each time the transfer callback gets called, exactly 312 bytes (thus 164 frames with each one having 2 bytes) are transfered.

However, what I do not understand is the setup of HW_PERIODS which is AFAIK the number of periods being transfered at a time ?

* What is the influence of this constraint on my ioplug plugin ?

* How does it change the way data is being transfered with the transfer callback ?

* What would be the correct setup for the mentioned application ?

cheers, stefan