Acquiring the current MODE refresh rate

Is there a way to determine the current MODE are fresh rate, other than counting VSync over a time period?

Can one assume that if the Mode specifier returned via OS_ScreenMode 1 is a MODE number, it’s at the default refresh rate and if not the Mode Selector Block does specify the Hz?

Now that we’ve started getting games that require 26bit modules running on the Pi, I’ve come across several that count VSync to determine the refresh rate and as ADFFS takes 1 sec after a MODE chnage to work out the Hz and then lock it to 50Hz, the game’s ensd up with the wrong refresh rate. As a consequence I need to know the refresh rate at Service_ModeChange and not have to kick off a VSync count.

Unfortunately it doesn’t look like there’s an easy, sure-fire way to get the current refresh rate.

• For numbered modes, the kernel will look for a mode definition which has the right refresh rate, but if it can’t find one then it will look for any mode with the desired resolution. But when you read back the mode using OS_ScreenMode 1 it will return the original mode number that was passed in.
• For mode selector blocks, if you set the refresh rate field to -1 when you switch mode, it will still be set to -1 in the block that’s returned by the OS. If it’s not -1 then it’s guaranteed to be that refresh rate.

I guess one approach you could take is to replicate some of the logic the OS uses:

• If it’s a mode number, construct a mode selector block for that width/height/bpp/refresh rate and issue Service_ModeExtension to get ScreenModes to translate it to a VIDC list (it should be a type 3 list). If the translation fails, set the refresh rate to -1 and try again. This request should succeed (there might be a couple of exceptional circumstances where it will fail, but I’d hope you’d never hit any of those)
• If it was a mode selector block then just pass it to Service_ModeExtension as-is

Once you’ve got the VIDC list you should be able to work out the refresh rate manually from the mode timings.