RA MAME: 1 frame of additional lag versus regular MAME

Hi,

Hopefully it’s allowed to crosspost from the the GitHub comments. I fiind it easier to discuss in these forums than on GitHub and I expect it to have a bit wider audience.

There’s a comment thread there about “1 frame of input lag in the RA core”: https://github.com/libretro/mame/issues/53

I’m also noticing the 1 frame of additional lag in RA MAME and can confirm it through use of the frame stepping method (pause+k) versus regular MAME. More importantly I accidentally stumbled upon an issue that may help uncover what’s going on.

It’s the game Pengo, if you run it with RA setting**

  • Poll Type Behaviour = Early AND
  • Frame Delay = 3 or higher

start the game, then it will complete each Act by itself instantaneously and indefinitely. So it loads a level and immediately you get the level completed tune and it moves to the next Act / Level, only to repeat the process indefinitely. Within 30 seconds (realtime) you’re at Act 10. The game reports for each level that it took about 1:40m to complete, so there’s something really strange going on.

Tested both in latest 0.198 and 0.199 RA MAME.

Note that this does NOT happen when Poll Type Behaviour is set to “Normal” or “Late” or with Frame Delay at 0 (zero), in that case it will run normal, just as regular MAME. Only happens when Poll Type Behaviour is set to “Early” and a Frame Delay of 3 or higher.

Since this is such an obscure “bug”, related to input polling, that maybe it is of help uncovering the 1 frame of additional lag of RA MAME versus regular MAME?

**EDIT: I tried to record a movie of it, but when recording is enabled the issue does not occur. I guess this may be because with recording enabled the Frame Delay gets disabled?