Re: IIGS Acceleration Idea
- From: Ed Eastman <noone@xxxxxxxxxxx>
- Date: Mon, 30 Jan 2006 08:59:25 -0600
Greg Andrzejewski wrote:
A stock GS has a "slow" mode at about 1 Mhz and a "fast" mode at 2.8 MHz. What is preventing us from simply making this "fast" mode something like 10 MHz?
In a word, the FPI/CYA chip. This is the thing that times and actually does everything, from the ram refresh to the slot timing to the mainboard and slot RAM addressing. To speed up the IIgs you'd have to implement a new CYA chip to produce all the timing and address signals for the main board plus the faster clock for the IIgs.
How to accelerate your IIgs without recreating the wheel:
1. Overdrive: Replace the CPU with a high speed CPU and simple 20x clock circuit. Monitor the Speed softswitch, and the HIGH pulse of the CPU clock along with the 'internal cycle' signals off the CPU. Turn those signals into drive for overclock circuit. Each internal cycle will be then 1/10 the normal time and be ready for the next activity at normal speed. Shoudl be 100% compatible and break nothing.
2. Freewheeling 65816: A little more complex, 100% compatible. Add fast CPU, clock, Ram and refresh circuit. Additional circuit to monitor the low clock pulse to 'freeze' the CPU to obey the FPI/CYA. Obviously circuit to route and clock Bank 0/1 (E0/E1) and Rom and Softswitches to main board, run the rest in the CPU RAM.
3. Reinvent the wheel, er IIgs mode: Build the same thing but instead of freezing the CPU on low clock from main board, ignore the main board completely except for: video ram updates and slot access. Monitor speed softswitch, Rom access, Softswitch access, drive activity, downshift/ sync to main board clock as necessary. aybe load ROMs to RAM and eliminate rom slowdown.
Want a block diagram? Want a wiring diagram? Can your read minds? THen nevermind.
Thankx, Ed .
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