VGA CRT Exact Refresh Rate

Is it possible to get my RPi4 (Lakka 3.2) via VGA CRT (HDMI to VGA) to output the exact refresh rate of arcade systems like Irem M72, Midway’s Mortal Kombat boards, and anything else that outputs lower than 60Hz (including 50Hz PAL)? Any specific video setting that can do this? The only sync setting I’ve found is related to G-Sync/Freesync which is not relevant to CRTs.

I’m not sure if lakka exposes the crt switchres options (yet?) but if it does, that’s the way to go.

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Thanks. I don’t see it yet. Hopefully it will included in upcoming releases. I am a bit curious as to how it works. Is it a wide 240p signal that will get generated, or will it still have the same vertical resolution as I’m currently using? (1280x1024)?

We are working on KMS switching. It does already work, really well. However, its very dirty code ATM. As soon as its ready we will expose the options on compatible OSes


Switchres is (mostly)for 240p/288p retro signals, on a common VGA monitor that requires double refreshrate, horizontal res depends on your setting (native, dynamic…).

You can output lower than 60 Hz refreshrates on VGA monitor, this requires high enough vertical resolution (higher than 240/288p) because of the 31 KHz limitation. I once fed a 576p 50 Hz signal to my Samsung for testing, the flickering was too intense to make this usable.

If you double the refresh rate and use BFI you can get 240/228p on a VGA monitor (31KHz) as well

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