Ability to set HDMI output refresh rate

[pizzarollsroyce]

I don't believe that Circle exposes a way to set the HDMI video output refresh rate to 50hz, which I'd like for a project I'm working on.

I tried looking for a mailbox register I could poke to do this, but I'm not able to find anything.

I'll note that if I boot into Raspbian, I can set it to 1280x720@50hz, so the hardware appears to support this.

[rsta2]

The only way to set the HDMI mode with Circle are the firmware settings in config.txt: https://elinux.org/RPi_config.txt#Video_mode_options Unfortunately this does not work on the Raspberry Pi 5 and your wanted target mode is not listed and thus probably not supported by the firmware. Raspberry Pi OS uses a kernel mode video driver now, not the firmware video support any more, and supports different options.

[pizzarollsroyce]

Ah, thanks for the detailed answer. Wish I had asked earlier.

I guess to allow a user to switch video modes, I'd need to use the SD card filesystem and update the config.txt file with that new configuration, then reboot (potentially after pulling down the EDID list to limit options to modes that the current monitor is compatible with)?

[rsta2]

You are welcome. Yes, the method, you have described, should work.