Re: [alsa-devel] Allocating buffers for USB transfers (again)
On 08/10/2011 04:32 PM, Alan Stern wrote:
Looking at the driver's current code, it appears that your patch does not fix the bug properly. Using discontiguous regions in the transfer buffer is perfectly okay. The real problem is later on, where you do:
if (send_it) { out->number_of_packets = FRAMES_PER_URB;
This should be
out->number_of_packets = outframe;
The way it is now, the USB stack will try to use data from all the frame descriptors, and the last few will be stale because the loop doesn't set them.
That's actually true, even though it doesn't seem to cause any trouble. I tested everything here of course, and the output URBs return back from the USB stack with their length fields zeroed out, which then causes the stack to send packets with zero-length fields at the end.
However, doing it right doesn't harm either. Thanks for spotting.
Takashi, can you apply this version?
Thanks, Daniel
At Wed, 10 Aug 2011 17:33:02 +0200, Daniel Mack wrote:
On 08/10/2011 04:32 PM, Alan Stern wrote:
Looking at the driver's current code, it appears that your patch does not fix the bug properly. Using discontiguous regions in the transfer buffer is perfectly okay. The real problem is later on, where you do:
if (send_it) { out->number_of_packets = FRAMES_PER_URB;
This should be
out->number_of_packets = outframe;
The way it is now, the USB stack will try to use data from all the frame descriptors, and the last few will be stale because the loop doesn't set them.
That's actually true, even though it doesn't seem to cause any trouble. I tested everything here of course, and the output URBs return back from the USB stack with their length fields zeroed out, which then causes the stack to send packets with zero-length fields at the end.
However, doing it right doesn't harm either. Thanks for spotting.
Takashi, can you apply this version?
Yep, applied now. Thanks.
Takashi
participants (2)
-
Daniel Mack -
Takashi Iwai