Snippet from earlier post:
>From: "Karl Regier" <reply@togroup.com>
>Subject: 1394 Iso Synchronization
>
>I am having a problem performing iso receives in a driver based on
the
>1394DCAM sample. In my driver, a "frame sized" buffer is passed to
the
>driver by the streaming interface, then that buffer is attached using
>REQUEST_ISOCH_ATTACH_BUFFERS with the Sy field set to 1 and the
>DESCRIPTOR_SYNCH_ON_SY field set. This implies to me that it should
wait
>for a packet with a Sy == 1 (indicating the first packet in a new
frame) and
>then continue to receive the data. The filled buffer (frame) is then
passed
>back to the streaming interface for display.
>
>This seems to work about 90% of the time. But quite often you see
>"glitches" in the video stream. It appears that a packet is missed,
causing
>a shift, and then the top of the next fram appears at the bottom of
the
>current frame. I am wondering if I am using these flags incorrectly,
or if
>the problem lies elsewhere.
>
I am experiencing the same symptoms using a driver that is not based
on the 1394DCAM sample. My driver attaches several buffers in stream
based mode, each large enough to contain a single frame of video data,
and sets the SYNCH_ON_SY flag. Everything works correctly most of the
time, the video is synchronized and all the frames are received. BUT
occaisionally packets are missing from the buffer and the end of the
buffer contains the start of the next frame. This bug does not appear
on all computers, and seems to be related to which OHCI card is being
used. But other DCAM drivers do not exhibit this problem.
Has anyone else experienced this problem and solved it? Or can anyone
suggest what I might be doing wrong?
Thanks!
Erik