50 fps v sync question

[twenty90seven]

I have my Windows resolution running at 50 fps, and with FS UAE have configured vsync to auto. When I press ctrl + F10 to check performance, I note the FPS alternating between 49.75 and 49.76. Presumably it should be a rock solid 50 instead? I notice this alternation between 49.75 and 49.76 for almost all games I play with FS UAE. I am typically running a stock standard Amiga 500 configuration with no filters or anything else that would make FS UAE run slower. I have to say though, Pinball Fantasies is scrolling very smoothly, with 49.75/49.76.

[jbl007]

Originally Posted by twenty90seven

Presumably it should be a rock solid 50 instead?

No, not necessarily. I don't know a single system which outputs the exact 50.000000000Hz. Some variations are normal. As long as the SYS and EMU values are exactly the same, it's fully synced.

[Retro-Nerd]

Just checked on my PC. FS-UAE shows 49.97-50.06Hz. Perfectly smooth for my eyes.

[Toni Wilen]

Real normal Amiga PAL rate is 49.92Hz. Only interlace is really 50Hz

[FrodeSolheim]

When you're running in vsync mode in FS-UAE, the Amiga refresh rate is "ignored" (as long as it is nearly equal to the host refresh rate), and the emulation speed is tuned to match the host refresh rate. So most likely, your host display is actually running at 49.75 Hz.

(Only when using G-Sync or similar technologies will the Amiga refresh rate be the "master" when syncing the displays.)

[Pat the Cat]

Makes no difference.

Real PAL Amigas will almost never run at 50Hz dead on - because they mostly take the timing information from the mains supply (which never runs at 50Hz dead on).

Big Box Amigas, that is. A2000, A3000, A4000. They have jumpers inside to set whether to use power line tick for timing (and extra bits in the power supply to provide that data) or start up a computed 50 or 60Hz rate from onboard circuitry instead. "Home" version Amigas always used onboard circuitry - which could switch from 50 to 60Hz and back using software (as could the big box Amigas). I am not too sure how the A1000 handled this, but as it was discontinued in 1987, there are very few A1000s left to check on.

It makes replacing or fixing power supplies from such machines more challenging than swapping out an ATX PSU on a PC. There isn't a "standard" Amiga power connector on big box Amigas. Unlike the A500, A600, A1200 - they all use pretty the same "brick". Although they differ in what maximum amps they can supply, and vary enormously in internal details (a lot were made in China using triode technology).

[Toni Wilen]

No, PS tick has nothing to do with vsync. It is only CIA "vsync" TOD counter that can be jumpered to use either vblank or power supply tick.

Display vsync/hsync (and other CIA "hsync" TOD) is always generated by Agnus which is clocked by ~28MHz crystal.

[Pat the Cat]

Originally Posted by Toni Wilen

No, PS tick has nothing to do with vsync. It is only CIA "vsync" TOD counter that can be jumpered to use either vblank or power supply tick.

Display vsync/hsync (and other CIA "hsync" TOD) is always generated by Agnus which is clocked by ~28MHz crystal.

Weird. So the CIA can run at one speed and the video system can run at a different speed?

Does not make sense to me, but we are going off topic, so I suggest I actually start looking at the old schematics I've been downloading.

It might make some of your data more understandable. You have to remember, I have 20 odd years of bullshit information to contend with.

[twenty90seven]

Thanks all for your answers, which makes me think that I have achieved sync. Certainly it looks like I have when I watch Pinball Fantasies and some demos (smooth vertical and horizontal scrolling). The only one I am having trouble with is SWOS, which shows some ghosting off the players. Still playing around with that.