Pipelined 6502/z80 with cache and 16x clock multiplier

Brett Davis · 2010-12-20T02:25:49+00:00

EETimes had an interesting article asking if 4-bits was dead.These chips have been pad limited for 2 decades, and as such areprobably manufactured at fabs that are beyond obsolete.You could take a public CPU design like OpenRISC and replace theinstruction decoder, and get an easy ~4x performance jump running65c802/65c816 code.Compatibility with the Apple// disk controller would be poor. ;)But lets ignore that for the moment, Apple made some work aroundsfor the Apple2GS, so that can be fixed.Step 2 would be to add a boot loader to set the cache modes upcorrectly for your memory spaces, so everything is not write through.That will get you another ~2x speedup.One should be able to do at least a 16x local clock multiplier, especially if the base clock is a pathetic 2 MHz.That will get you another ~8x speedup.The end result will be a ~quarter of the speed of the native OpenRISCopcodes, due to being register starved, but close enough not to matter?Compatibility is important.The end result would still be pad limited and tiny, and made at astill obsolete if newer fab.Is there a market for a 6502 era CPU that ran ~10x faster at ~10% more cost?I think I just described the AVR8 family of CPUs, so the answerwould be yes...Brett- Merry Christmas

Dec 20, 2010 101 Replies

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I never saw the BBC machine. DeSmet (Aztec) C for the Apple was full ANSI in its final incarnations.

The //gs system software is available free here:

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The APW tools seem to have disappeared from Apple's site - they were there in December 2010 when I made the previous post. They APW tools were based on ByteWorks ORCA tools which are still available.

An early version of APW is available free from:

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The ORCA environment and compilers are available for $$$ (though reasonable) from

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I originally found the APW stuff googling 65816 developer tools, so it's possible they are mirrored somewhere ... but I can't find them again just now.

There are free 65816 C and Pascal compilers. You can get the ByteWorks C and Pascal GS/OS and //gs toolbox interfaces from Syndicomm and cobble together a developer system.

APW didn't have an APDA sanctioned Pascal. ORCA/Pascal was the plug-in Pascal for APW. Overall ORCA was a better compiler, but TML's integrated debugger made it a nicer development environment.

TML (now Complete Pascal) for //gs is available here:

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George

Pipelined 6502/z80 with cache and 16x clock multiplier

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