[alsa-devel] USB asynchronous mode feedback format

Alex Lee lee188 at singnet.com.sg
Fri Oct 15 15:31:50 CEST 2010


On Fri, 2010-10-15 at 15:04 +0200, Julian Scheel wrote:

> Ah right, thanks.
> Well now I swapped data[1] and data[2]. When monitoring the amount of data I 
> get per read, it is constant at 192bytes, which would be expected for feedback 
> ratio of 48, right? But if I have 0x06 to 0x07 for example I do still get 
> exactly 192bytes per read, shouldn't I get less data in that case? (I always 
> try to read up to MAXPACKETSIZE which is 512, btw)

Suggest:

(1) The feedback rate has to fall withing +/- 10% of the nominal rate.
Otherwise it is ignored.

(2) You need to find out exactly how many samples the host sends you.
Look at my sdr-widget code, for example.  Then you read what the host
sends you.

(3) Do a > dmesg | tail 
    after unplugging and plugging your USB device in.  Then you can see
whether there are any errors in your syncpipe

btw, what is your Linux kernel version?

Alex




More information about the Alsa-devel mailing list