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Just a thought Faster 68000 Cpu in MD1??

Dr_Frankenmiga - Oct 27, 2003

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		Epicenter	Sep 7, 2004
		Of course they're not identical, but what differences do you think would cause problems with an appropriate adapter? I wish I could say, but I didn't build the device .. I don't know it too well. But I HAVE used 68040 accelerators for 68030, 68020-based Macintoshes and they did NOT function at all without their software. There was absolutely no performance increase until it was installed.     Did you try to overclock the VDP too? Quite risky since the vdp is already very fast (53mhz). If you push it to 2*53mhz, maybe the framerate will be 2time faster without garbages. When you play at a segacd or 32x game with the overclocked system, whats appen? For exemple, could you try sonicCD or Bcracer? Ho, what's about the 32x? Both sh2 may run at 30mhz without serius problem... I can't overclock the VDP withot pushing up the vertical sync beyond 60 Hz, that would be problematic because nothing could display the video output. Maybe a very rare RGB display, but I'm not aware of one. As for the Sega CD. If you try to *boot* at a higher speed into the Sega CD BIOS at 12 MHz or higher it will crash-- but if you start at 7.6, then switch to 12+ MHz when it's already running it's usually fine. Some games you will see a difference, some you won't-- some SCD games rely on the MegaDrive's 68000 and not the Sega/Mega CD's 68000. The ones using the MCD's 68000 (at 12 Mhz) predictably have some speedup already. It probably is possible to overclock the 32x. Maybe I will do so in the future.

		ExCyber	Sep 7, 2004
		Using the upper 8 bits of addresses has caused problems for all m68k platforms when switching CPU . Yes, using them obviously opens up problems. I was assuming an adapter that pulled them down.     At least the MOVE for SR instruction exists only on the 68000 (and 68008), others change their meaning subtly (eg. MOVEM). MOVE from SR and MOVE to SR do exist on 68010 and later, but they are privileged. I guess the danger there is that a stray MOVE to SR instruction could throw the later procs into user mode. This could probably be filtered by a rudimentary OS, but then we're getting into a lot more than just a simple processor swap and may as well target ColdFire.

		antime	Sep 7, 2004
		Originally posted by Epicenter+Sep 7, 2004 @ 06:04 PM--><div class='quotetop'>QUOTE(Epicenter @ Sep 7, 2004 @ 06:04 PM)</div><div class='quotemain'>I don't know it too well. But I HAVE used 68040 accelerators for 68030, 68020-based Macintoshes and they did NOT function at all without their software. There was absolutely no performance increase until it was installed.[/b] You need system software to enable and initialize the caches. On the Amiga, you also need to set up the MMU for fastram. <!--QuoteBegin-E xCyber@Sep 7, 2004 @ 07:11 PM MOVE from SR and MOVE to SR do exist on 68010 and later, but they are privileged.[/quote] You're right, the privileged instructions were just listed in another part of the manual.

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