Dear all ~~
I have met a issue when I used the mmap method for previewing . I just
used the standard code as spec to get the image data :
status_t CameraHardwareProwave::V4l2Camera::v4l2CaptureMainloop()
{
LOG_FUNCTION_NAME
int rt ;
unsigned int i ;
fd_set fds ;
struct timeval tv ;
struct v4l2_buffer buf ;
for(;;){
FD_ZERO(&fds) ;
FD_SET(v4l2Fd, &fds) ;
//now the time is long ,just for debug
tv.tv_sec = 2 ;
tv.tv_usec = 0 ;
rt = select(v4l2Fd + 1, &fds, NULL, NULL, &tv) ;
LOGD("The value of select return : %d\n", rt) ;
/********** for debug
if(V4L2_NOERROR != v4l2ReadFrame()){
LOGE("READ ERROR") ;
}
***********/
if(-1 == rt){
LOGE("there is something wrong in select
function(select)") ;
//no defined error manage
return V4L2_IOCTL_ERROR ;
}
if(0 == rt){
LOGE("wait for data timeout in select") ;
return V4L2_TIMEOUT ;
}
memset(&buf, 0, sizeof(buf)) ;
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
buf.memory = V4L2_MEMORY_MMAP ;
if(-1 == ioctl(v4l2Fd, VIDIOC_DQBUF, &buf)){
LOGE("there is something wrong in dequeue
buffer(VIDIOC_DQBUF)") ;
return V4L2_IOCTL_ERROR ;
}
assert(i < n_buf) ;
LOGE("buf.index 0buf.length = %d %d \n", buf.index ,
buf.length) ;
memcpy((mCameraProwave->getPreviewHeap())->base(),
v4l2Buffer[buf.index].start, buf.length) ;
if(-1 == ioctl(v4l2Fd, VIDIOC_QBUF, &buf)){
LOGE("there is something wrong in enqueue
buffer(VIDIOC_QBUF)") ;
return V4L2_IOCTL_ERROR ;
}
//break ; //i don't know whether the break is needed ;
}
return V4L2_NOERROR ;
}
when executed the VIDIOC_DQBUF IOCTL,the return value was right, but the
value of buf.length would always be zero. Then I used the read()
function to read raw data in the file handle for debug, and I can get
the raw data. Anybody have met this issue before ? Who can give me some
advices or tell me what is wrong , thanks a lot ~
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