Hello,
could please anyone explain me a bit situation about using memory buffers
for dma for video input devices? Unfortunately I don't understand it at
all.
I want to capture images 1600x1200 from 2 mpix sensor on i.mx27 board.
I gave 8MB to mx2_camera device with dma_declare_coherent_memory.
Unfortunately it seems to be not enough. In UYVY format I need 1600x1200x2
for one picture, it is cca 3.8MB.
After some digging I noticed, that dma_alloc_coherent() is called three
times and each time with the 3.8MB demand. Once it is directly from
mx2_camera driver and two times from videobuf_dma_contig. OK, that is more
than 8MB available, but why there are so big memory demands for one
picture?
I'm using gstremer for capturing, so it probably requests several buffers
with VIDIOC_REQBUFS. Is this behaviour normal, even if there is explicitly
noted that I want only one buffer?
gst-launch \
v4l2src num-buffers=1 device=/dev/video1 ! \
video/x-raw-yuv,format=\(fourcc\)UYVY,width=$WIDTH,height=$HEIGHT ! \
jpegenc ! \
filesink location=col_image.jpg
with best regards
Jan
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