Em Thu, 23 Apr 2009 19:15:14 +0900
"Dongsoo, Nathaniel Kim" <dongsoo....@gmail.com> escreveu:
> Hello Hans,
>
> Is it an ordinary way to use twice reqbuf without closing and
> re-opening between them?
>
> I mean like this,
>
> 1. Open device
> 2. VIDIOC_REQBUFS
> <snip>
> 3. VIDIOC_STREAMON
> <snip>
> 4. VIDIOC_STREAMOFF
> 5. VIDIOC_REQBUFS
> <snip>
> 6. VIDIOC_STREAMON
>
> I suppose there should be a strict order for this. That order seems to
> be wrong but necessary when we do capturing a JPEG data which size
> (not resolution) is bigger than the preview data size. (Assuming that
> user is using mmap)
> Please let me know the right way for that kind of case. Just close and
> re-open with big enough size for JPEG? or mmap with big enough size in
> the first place?
That's a very good question.
You shouldn't be needing to close/open the device for this to work, but between
(4) and (5), you'll need to call VIDIOC_S_FMT, to change the videobuf size,
and, to be safe, unmap the videobuf memory.
A code like the above may give different results depending on the way
videobuffer handling is implemented.
A good idea is to test it with vivi driver (that uses videobuf), with debugs
enabled, and compare with other drivers.
I did such test with vivi and it worked properly (although I didn't change the
data size).
If you want to test, I used the driver-test program, available at the
development tree, with the patch bellow. I didn't actually tested to resize the
stream, but from vivi logs, the mmapped buffers seem to be properly
allocated/deallocated.
Cheers,
Mauro
diff --git a/v4l2-apps/test/driver-test.c b/v4l2-apps/test/driver-test.c
--- a/v4l2-apps/test/driver-test.c
+++ b/v4l2-apps/test/driver-test.c
@@ -30,7 +30,7 @@ int main(void)
{
struct v4l2_driver drv;
struct drv_list *cur;
- unsigned int count = 10, i;
+ unsigned int count = 10, i, j;
double freq;
if (v4l2_open ("/dev/video0", 1,&drv)<0) {
@@ -97,45 +97,47 @@ int main(void)
fflush (stdout);
sleep(1);
- v4l2_mmap_bufs(&drv, 2);
+ for (j = 0; j < 5; j++) {
+ v4l2_mmap_bufs(&drv, 2);
- v4l2_start_streaming(&drv);
+ v4l2_start_streaming(&drv);
- printf("Waiting for frames...\n");
+ printf("Waiting for frames...\n");
- for (i=0;i<count;i++) {
- fd_set fds;
- struct timeval tv;
- int r;
+ for (i=0;i<count;i++) {
+ fd_set fds;
+ struct timeval tv;
+ int r;
- FD_ZERO (&fds);
- FD_SET (drv.fd, &fds);
+ FD_ZERO (&fds);
+ FD_SET (drv.fd, &fds);
- /* Timeout. */
- tv.tv_sec = 2;
- tv.tv_usec = 0;
+ /* Timeout. */
+ tv.tv_sec = 2;
+ tv.tv_usec = 0;
- r = select (drv.fd + 1, &fds, NULL, NULL, &tv);
- if (-1 == r) {
- if (EINTR == errno)
- continue;
+ r = select (drv.fd + 1, &fds, NULL, NULL, &tv);
+ if (-1 == r) {
+ if (EINTR == errno)
+ continue;
+
+ perror ("select");
+ return errno;
+ }
- perror ("select");
- return errno;
+ if (0 == r) {
+ fprintf (stderr, "select timeout\n");
+ return errno;
+ }
+
+ if (v4l2_rcvbuf(&drv, recebe_buffer))
+ break;
}
- if (0 == r) {
- fprintf (stderr, "select timeout\n");
- return errno;
- }
-
- if (v4l2_rcvbuf(&drv, recebe_buffer))
- break;
+ printf("stopping streaming\n");
+ v4l2_stop_streaming(&drv);
}
- printf("stopping streaming\n");
- v4l2_stop_streaming(&drv);
-
if (v4l2_close (&drv)<0) {
perror("close");
return -1;
--
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