Hi, On 09/04/2009 05:14 AM, Andy Walls wrote:
The V4L2 spec for the read() call seems unlcear to me: "Return Value On success, the number of bytes read is returned. It is not an error if this number is smaller than the number of bytes requested, or the amount of data required for one frame. This may happen for example because read() was interrupted by a signal. On error, -1 is returned, and the errno variable is set appropriately. In this case the next read will start at the beginning of a new frame." To me, the spec only says the remainder of a frame is thrown away when read() exits with an error.
It does seem to say that yes, as said in a previous mail of me, this part of the spec needs some fixing. It seems to try and describe the queuing that happens inside the driver in too much detail and leaves out other much me important bits about how read() on video devices behaves.
BTW, should select() return "data available", if less than one whole frame is available? It can happen if the buffers we give to the CX23418 firmware don't exactly match the YUV framesize. The V4l2 spec for the read() call seems to imply that read() should block (or return with EAGAIN) until at least one whole frame is available. Is that correct?
I agree that waiting until at least one whole frame is available. Is the correct behaviour. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
