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CPU overlocking by FPGA and RAM replacement
Post Posted: Wed Oct 13, 2021 6:22 pm
I saw this: http://www.e-basteln.de/computing/65f02/65f02/ which is a 6502 CPU replacement that extracts the memory map contents and then runs at about 100x speed apart from when it’s accessing memory mapped things. It seems this would be even easier for Z80 where you have a separate IO bus, but would also require reading the ROM (with paging) into the FPGA RAM. I don’t have anything like the ability to do this, but I thought it’s interesting to hypothesise about and I thought the memory copying was a clever way to bypass those speed limits with old Z80 variants and clock hacks in hardware.
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  • Joined: 14 Aug 2000
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CPU overlocking by FPGA and RAM replacement
Post Posted: Thu Oct 14, 2021 8:17 am
Very cool. But would there be any game software that benefitted from it?

I overclocked the SMS Z80 to 4.6MHz some time ago, and that increase was enough to get rid of the frame-skipping in Power Strike.

I remember a chess game on the Amiga I think, where if you set the CPU player to the highest difficulty level of "evil genius", the CPU player would take a full 10 seconds to calculate its next move. So I suppose that's one game that could use it. :)
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Post Posted: Thu Oct 14, 2021 8:40 am
Sega Chess at the highest difficulty level is incredibly slow :) Indeed the aim of the linked project is to target chess computers and make them practical to play at higher difficulty levels.

I think as a first approximation, a game running at 10-15fps might get up to 60fps with a 4-6x boost, but that will not work if the game is limited by other things - some games are deliberately limited by how they time updates (eg do half the work on even frames and half on odd) and how they are limited by VDP bandwidth (only doing as much per frame as the VDP will allow).
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Post Posted: Thu Oct 14, 2021 10:20 am
I wonder if the CPU overclock register on the Mega Drive works for the Mega Drive's Master System compatibility mode.

Obviously, the problem is that this also affects the PSG's input clock. Unless you all enjoy everything being two and a quarter times higher pitched.
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Post Posted: Thu Oct 14, 2021 11:00 pm
10 seconds to calculate one move doesn't sound the slowest chess game there is.

I've heard of games that can take MINUTES at the highest difficulty (was it Jeremy Parish review of SNES Chessmaster where he recorded a single move).

Maybe it was 2600 Atari Chess I heard of that could take hours to calculate a move.
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