On Thursday 14 February 2002 03:31 pm, Alan Cox wrote: > Its a ring buffer. When you start capturing the kernel starts filling > all the available buffers one per frame. As you finish with each frame > in the shared buffer you tell the kernel via the ioctl and it becomes > eligible for reuse. > > The driver runs round and round the ring chasing after you. If the driver > catches up with you in the ring it will start dropping frames What if I get ahead of the kernel? If I'm ready for frame #2, but it hasn't finished streaming off the usb port yet, how does the kernel indicate to me that frame #2 doesn't contain good data yet? (or in my case, how does my driver tell a calling program "not yet"?) Do I need to call VIDIOCMCAPTURE once per frame? If it is a ring buffer, what is the function of the video_mmap.frame ? Does it indicate which of the available frames the first one should be spooled to? And did I get the expected calling sequence right? (VIDIOCGMBUF, allocate mmap in userspace, call mmap file op, VIDIOCMCAPTURE, VIDIOCSYNC)
