How to Enable RGB Full Color range over HDMI in Text Mode

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 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.

We have confirmed full range mode is not supported on Jetson Nano. Please run in limited range mode.

Hi DaneLLL,
Is this a HW issue or driver issue?
if driver issue, can I modify the kernel driver code to force enable it?

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