Andy Ng wrote:

I am quite surprised that by sending hardware params with alsa-lib the prepare function is called automatically in the driver.

In my case, I would like to open and configure pcmNp and pcmNc and then call prepare for pcmNp and pcmPc channels.

It is quite imperative to execute specific configuration steps after both channels are opened and configured.

What configuration steps? Is there some dependency or shared resource between the two streams? In that case, you have to set the SNDRV_PCM_INFO_JOINT_DUPLEX flag, and do whatever is necessary in the first hw_params call, and just check for correctness in the later hw_params call of the other stream.

I was wondering if there is any ioctl interface that can be hooked in alsa-lib to pass extra configuration info before start the streams.

No.

Regards, Clemens