I have a basic mmap question I hope I can get some help with.
I haven't been able to find a clear example of using it with a camera, so
please excuse my ignorance.
My code pretty much works, but there are some performance issues.
This is how I initialize the mmap
ioctl(camera_fd, VIDIOCGMBUF, &vid_mbuf);
grab_size = grab_buf.width * grab_buf.height * 3;
picture = mmap(0, grab_size, PROT_READ | PROT_WRITE, MAP_SHARED,
camera_fd, 0);
-- This should make it so I am sharing a 1 frame buffer with the camera (an
OV511)
To read it, I do
grab_buf.frame = 0;
if (pthread_mutex_lock(&camera_mem_mutex))
pthread_exit(NULL);
if (ioctl(camera_fd, VIDIOCMCAPTURE, &grab_buf) == -1)
{
pthread_mutex_unlock(&camera_mem_mutex);
perror("ioctl VIDIOCMCAPTURE");
return 0;
}
if (ioctl(camera_fd, VIDIOCSYNC, &grab_buf.frame) == -1)
{
pthread_mutex_unlock(&camera_mem_mutex);
perror("ioctl VIDIOCSYNC");
return 0;
}
pthread_mutex_unlock(&camera_mem_mutex);
-- Here (inside a thread) I am "safely" waiting for frame 0 to "sync" -
which I assume means get filled from the camera.
Sometimes I get stuck waiting for VIDIOSYNC.
Is this the correct order of operation? Can I set the camera up to use
multiple frames effectively? Is is worth it?
-- Devin
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