(Moving this discussion from sdr-widget to alsa-devel. Can't Cc: the original mailing list as it forbids cross-posting)

On Thu, Jun 10, 2010 at 09:36:48PM -0700, Alex Lee wrote:

I studied the driver source again and it becomes apparent that the driver only looks at the MIN value of the triplet (MIN, MAX, RES). It does not take into consideration of the MAX and the RES in each triplet.

For samplerates it does that, yes.

The driver calculates its own MIN and MAX values by going through all the triplets in the clock source. In the present firmware, we only have ONE triplet in each clock source, with:

# of triplets = 1 (2 byte value) MIN 48000 MAX 96000 RES 48000

Ah, that's a corner case I didn't see. I'll fix this.

in accordance with the UAC2 specs. The present driver code expects:

# of triplets = 2 (2 byte value) triplet 1:

MIN 48000 MAX 48000 RES 00000

triplet 2:

MIN 96000 MAX 96000 RES 00000

Yes, that's right. All firmware code I've seen so far also has a triplet for each discrete sample rate.

Thus the present driver cannot decode the 1st case above correctly, and only get the 48khz value.

I will update the firmware to cater to the 2nd case above and we should have the 96khz back :-)

Ok, fair fix. I'll make sure future versions of the driver also support the other approach.

Thanks, Daniel