On Fri, 25 May 2018, John Sledge <john_sledget@xxxxxxxxx> wrote:
> Hi Jani,
> I seek 0-800 and here's what I get, all 11 0A in hex. Not sure if this is the brightness value of the display. I also did a test, when I disconnect the DP to the display and execute the dd commands, it would say error reading 'dev/drm_dp_aux1': Connection timed out. So I think my display setup is okay and the 11 0A values are really coming out from the display.
> Output in hex:11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A 11 0A ....
>
> int main(int argc, char **argv)
> { int ret = 0; int offset = 0; char call[100]; for(offset=0;offset<800;offset++) { sprintf(call,"dd if=/dev/drm_dp_aux1 bs=1 count=2 seek=%d >> out.txt",offset); ret = system(call); } return 0;}
Look, in this case dd is for debugging and testing on the command line,
to verify your approach before writing C. For your real thing, use the
open, read, write, lseek system calls. Don't call dd from C.
I've directed you to the right direction, and this is the right place to
ask about drm and kms related stuff. But for the basics, you might be
better off asking at stackoverflow or something.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
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