Re: IIGS Acceleration Idea

[Ed Eastman <noone@nowhere.net>]

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