On 16.11.2012 10:39, Daniel Griscom wrote:
At 7:22 AM +0800 11/16/12, Daniel Mack wrote:
Hi Daniel, Hi Elad,
On 16.11.2012 05:32, Daniel Griscom wrote:
At 10:02 PM +0100 11/15/12, Eldad Zack wrote:
Hi Daniel,
On Thu, 15 Nov 2012, Daniel Griscom wrote:
I'm having trouble getting implicit feedback working with my custom capture/playback USB audio class device, even with the latest kernel. I presume it's a problem with my device's configuration, but can't figure out exactly what the problem is (after a whole lotta investigation).
What exactly doesn't work?
The audio output stream (from the computer to my device) runs at a few frames per second higher or lower rate than that of the input stream (from my device to the computer). The actual difference seems to be stable on a specific machine, but varies greatly between machines (I've seen differences from +7fps to -2fps; I presume this is due to differences in CPU clock frequencies).
So you're saying that this is what you experience after you added code to make the driver use the implicit feedback mechanism? Over which time did you measure this and how exactly? Because frankly, I doubt that - the data rate is purely derived from the number of incoming samples.
This has been the case for a while; we started work with ALSA 1.0.23, but upgrading to kernel 3.6.6 (with included ALSA code) didn't change anything. We have yet to do any patching of ALSA for this matter.
Well, afaik, ALSA 1.0.23 is what ships with a kernel <= 3.4, and the code for implicit feedback went in for 3.5.
Does your device demand the same number of *bytes* or samples/channel to be sent?
I'll have to check that.
Let me rephrase the question: does the number of input and output channels match? Eldad had a patch in his series that should make it work for both scenarios.
The code I wrote for implicit feedback is used by the M-Audio FTU devices,
So, with an FTU the implicit feedback code works?
Yes, it does for many others.
What version of kernel/ALSA should I use - the latest?
Yes, always use the latests from git, especially for such relatively new features.
Daniel