NTSC MiniMig

[Piru]

How did the later Amigas support both NTSC & PAL?

Only the video output changes, so they don't actually support the other system 100%.

ECS added beamcon0 bit 5 to toggle between PAL and NTSC preprogrammed modes. See BEAMCON0 bit 5 (PAL).

[Piru]

@alexh

Actually, I'm pretty sure that "real" PAL machines when toggled to NTSC don't actually change the frequency of the CPU or CIAs. Think about it: You can toggle between PAL and NTSC realtime. If the full system clocking would change when you do, any running timers would run too fast or slow, depending on which screenmode is visible.

Clearly this is not the case.

Real NTSC machines run at slightly higher CPU and CIA clock, indeed, but IMO this is unrelated to the display mode (they will continue to run faster even when displaying PAL screen).

[Piru]

@alexh

And I thought they did. Hence why the music (on some replay routines) is faster in NTSC than PAL.

However it may just be that they use the VBL interrupt to time music playback which will make the music faster?

Yeah, that's it. It indeed happens because these routines are tied to vertical blank frequency (50Hz for PAL, 60Hz for NTSC). Player-routines which use CIA timers do not have this problem, they continue playback exactly the same speed, regardless of the screenmode.

Think about it, if CIA timers would change speed depending on the screenmode, the system clock would run too slow/fast, too, causing the clock to drift. That'd be unacceptable.

[Piru]

@freqmax

So does this mean I can remove the obviously wrong quote from alexh? (about system running at different speed when you toggle between PAL/NTSC display modes.. Amiga bus clock does NOT change, nor the CPU clock)

Some music players run at different speed because they're timed to the vertical blanking frequency, and not CIA timers (vertical blank rate is 50Hz for PAL and 60Hz for NTSC, CIA timer speed remains the same regardless of the display mode. PAL and NTSC systems do have different system base clocks and thus different CIA clocks. The system base clock - and thus the CIA base clock - do not change depending on the screenmode). The only speed gain in 3D games from NTSC is the smaller area to render.

*edit*

Now that I think about it, what MiniMig probably wants is the full deal: Changing the base clock aswell (that is really change between PAL and NTSC, not just the display mode). However, this cannot be done runtime (restart is needed).

[Piru]

@alexh

I think an NTSC Amiga will have a faster bus/CPU clock than it's PAL rival, but it is so small.

Yes. However, PAL system displaying NTSC screen doesn't have this benefit.

[Piru]

@freqmax

The problem is that the CIA base frequency is determined at a very early stage during the system boot. This means that if you change the timing runtime the CIAs will run either too fast or slow.

[Piru]

@Doobrey

That still would not work. Any app can get the eclockfrequency and store it locally. There is no way to patch these. And how about some currently running CIA timer? Would you just make this timer run too fast/slow?

[Piru]

@leirbag28

Nowhere was I disputing the fact that games that have both NTSC and PAL versions run faster in NTSC. There is after all less to render, aswell as less bitplane data to fetch with DMA. Faster screen refresh (60Hz vs 50Hz) is also often perceived as "running faster", if the game speed is locked to the VBL.

What I said was: toggling betweek PAL and NTSC screenmodes does not change the system base clock or the CIA clock. CPU runs exactly the same speed, too.