I have a jetson nano board running ubuntu18.04, In Text Mode by DRM driver, I want to draw some raw pixels to monitor over HDMI.
To use DRM, I did following step:
1:systemctl set-default multi-user.target and reboot
2: apt install libdrm-dev
3: git clone GitHub - dvdhrm/docs: API Documentations, HowTos and Tutorials
4: build, make and test modeset , it seems woks, the monitor is colorful as expected.
5: modify source code. (uint32_t)&buf->map[off] = 0x00; —> force fill the framebuffer with 0 to show “black” on monitor.
6: then test. the result is unexpected. the monitor is not pure black, it look slight backgroud of “white” .
According to RGB color Range, 0-255 is responsible for full mode while16-235 is responsible for limited mode.
So It seems that the device is working under limited mode.