Support cores with refresh rate higher than primary display

[mitchmindtree]

Thanks for your work on Lemuroid, it seems like a lot of fun!

I tried running a Pokemon Silver ROM, and while it appears to work well in GBCoid, it runs in slow motion on Lemuroid. By slow-motion, I mean the game appears to run consistently at around 2/3 of the original speed.

Going into the settings while in-game and pressing the fast-forward button causes the game to speed up, but becomes much too fast. Is there a way to tweak the playback rate? Or perhaps some other settings I should try messing with to get the expected behaviour?

While GBCoid runs at the correct rate, the audio has some severe clipping in polyphonic sections and saving doesn't work. I also much prefer the virtual gamepad layout of Lemuroid and that the position of the screen is closer to the top of the display in portrait 👍

Phone: Hisense A5 Pro CC (Oct-core 1.8ghz android phone with colour e-ink display)
Android 10
Lemuroid 1.8.0-beta1

[Swordfish90]

Hi @mitchmindtree . Thank you for reporting this. The issue is that Lemuroid currently can't go faster than your display refresh rate. I'm guessing here your e-ink display doesn't reach 60hz but rather ~40hz or (~80hz with fast-forward enabled).

It's definitely an interesting feature, which will also be useful for consoles that don't run at 60hz (such as the Atari Lynx).

[mitchmindtree]

Good spot, this indeed seems to be the issue. Running OpenGL gears demo (which uses vsync) shows the phone running consistently at 42 FPS.

Do you know if it's possible in Android to slow the refresh rate of the display system-wide? I wonder if it's possible to force my display to 30 FPS and then use the fast-forward button in lemuroid.

But yes, having the option to detach display rate from the gameplay clock would be nice. Does this limitation currently come from libretro?

[Swordfish90]

Thank you for double-checking it. I guess we have gathered enough evidence. Timing is entirely up to the frontend, so there is no inherent limitation within Libretro.

I guess tampering with the default refresh rate will not be straightforward (maybe root and custom kernels?), so the best solution is definitely implementing this.

[Swordfish90]

Hi @mitchmindtree . I just gave this a go. Would you be available for a quick test to confirm that the timing is correct also on your device?

Here you can find a debug build, it can be installed alongside the release version: https://drive.google.com/file/d/1UDHyb4TJNWPjU1_ENh5J7gbC5VAZKAVs/view?usp=sharing

[mitchmindtree]

Nice work, this appears to work beautifully out of the box with both Silver (GBC) and Soul Silver (NDS)! Thanks for the quick response and patch, and for hacking on such a fun project :)

[Swordfish90]

Thank you for taking a look at the test build. I'll merge the changes with the next major release 1.9.0.

[Swordfish90]

I just released 1.9.0 which includes this fix, so I'm closing the issue. Feel free to let me know if something else feels wrong with it.