v4l2 simple application - performance problem - c

Question

I have a very simple setup where a camera connected to a Pi Zero is triggered by an external signal.
Problem: Achievable framerate is <0.4fps with my code using v4l2. Works fine with e.g.: raspivid.
With raspivid 1920x1080 # 50fps works as expected (tested using -pts to save timecodes). My code instead will never dequeue a buffer at 50Hz. I have to reduce the trigger rate to 5Hz before receiving frames every ~600ms! This looks like I'm still only receiving every third frame. The returned framebuffers always skip one index:
new frame 0: 3110400
time diff 0.6006
new frame 2: 3110400
time diff 0.6006
new frame 4: 3110400
time diff 0.600601
new frame 6: 3110400
time diff 0.6006
You can find my code below (exposure setup,... removed)
Question: Can you give me a hint what could be the problem? The program does nothing but dequeue and enqueue the buffers so performance should not be an issue.
#define NB_BUFFER 10
int main(int argc, char *argv[])
{
int exposure = 50;
int rows = 1080;
int cols = 1920;
if(argc > 1){
exposure= atoi(argv[1]);
}
if(argc > 3){
cols=atoi(argv[2]);
rows=atoi(argv[3]);
}
struct vdIn vdin;
struct vdIn *vd = &vdin;
if((vd->fd = open("/dev/video0", O_RDWR)) < 0){
perror("open");
exit(1);
}
if(ioctl(vd->fd, VIDIOC_QUERYCAP, &vd->cap) < 0){
perror("VIDIOC_QUERYCAP");
exit(1);
}
if(!(vd->cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)){
fprintf(stderr, "The device does not handle single-planar video capture.\n");
exit(1);
}
vd->fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd->fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_SBGGR8;//V4L2_PIX_FMT_BGR24;
vd->fmt.fmt.pix.width = cols;
vd->fmt.fmt.pix.height = rows;
if(ioctl(vd->fd, VIDIOC_S_FMT, &vd->fmt) < 0){
perror("VIDIOC_S_FMT");
exit(1);
}
struct v4l2_control control;
control.id = V4L2_CID_EXPOSURE_AUTO ;
control.value = V4L2_EXPOSURE_MANUAL;
if(ioctl(vd->fd, VIDIOC_S_CTRL, &control) < 0){
perror("VIDIOC_S_CTRL EXPOSURE MANUAL");
exit(1);
}
.... iso manual, line frequency off, set exposure, auto whitebalance off
vd->rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd->rb.memory = V4L2_MEMORY_MMAP;
vd->rb.count = NB_BUFFER;
if(ioctl(vd->fd, VIDIOC_REQBUFS, &vd->rb) < 0){
perror("VIDIOC_REQBUFS");
exit(1);
}
int ret;
/* map the buffers */
struct v4l2_buffer buf;
for (int i = 0; i < NB_BUFFER; i++) {
memset (&vd->buf, 0, sizeof (struct v4l2_buffer));
vd->buf.index = i;
vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd->buf.memory = V4L2_MEMORY_MMAP;
ret = ioctl (vd->fd, VIDIOC_QUERYBUF, &vd->buf);
if (ret < 0) {
fprintf (stderr, "Unable to query buffer (%d).\n", errno);
return -1;
}
std::cout << "buf len " << vd->buf.length<<std::endl;
vd->mem[i] = mmap (0 /* start anywhere */ ,
vd->buf.length, PROT_READ, MAP_SHARED, vd->fd,
vd->buf.m.offset);
if (vd->mem[i] == MAP_FAILED) {
fprintf (stderr, "Unable to map buffer (%d)\n", errno);
return -1;
}
}
/* Queue the buffers. */
for (int i = 0; i < NB_BUFFER; ++i) {
memset (&vd->buf, 0, sizeof (struct v4l2_buffer));
vd->buf.index = i;
vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd->buf.memory = V4L2_MEMORY_MMAP;
ret = ioctl (vd->fd, VIDIOC_QBUF, &vd->buf);
if (ret < 0) {
fprintf (stderr, "Unable to queue buffer (%d).\n", errno);
return -1;
}
}
// Activate streaming
int type = vd->fmt.type;
if(ioctl(vd->fd, VIDIOC_STREAMON, &type) < 0){
perror("VIDIOC_STREAMON");
exit(1);
}
bool capture_is_running = true;
double lastTimestamp=0;
while(capture_is_running){
memset (&vd->buf, 0, sizeof (struct v4l2_buffer));
vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd->buf.memory = V4L2_MEMORY_MMAP;
std::cout << "try to dequeue" << std::endl;
ret = ioctl (vd->fd, VIDIOC_DQBUF, &vd->buf);
if (ret < 0) {
fprintf (stderr, "Unable to dequeue buffer (%d).\n", errno);
return -1;
}
cout << "new frame "<<vd->buf.index<<": "<< vd->buf.bytesused << endl;
double timestamp = vd->buf.timestamp.tv_sec + vd->buf.timestamp.tv_usec/1000000.;
double timeDiff = timestamp - lastTimestamp;
lastTimestamp = timestamp;
std::cout << "time diff " << timeDiff << std::endl;
ret = ioctl (vd->fd, VIDIOC_QBUF, &vd->buf);
if (ret < 0) {
fprintf (stderr, "Unable to requeue buffer (%d).\n", errno);
return -1;
}
}
// Deactivate streaming
if(ioctl(vd->fd, VIDIOC_STREAMOFF, &type) < 0){
perror("VIDIOC_STREAMOFF");
exit(1);
}
close(vd->fd);
return EXIT_SUCCESS;
return 0;
}