14mhza500 on aminet

[DamageX]

I was looking for plans for an amiga->VGA cable (which I did find, and build) and I came across this 14MHz A500 hack which involves simply swapping in a suitably-rated 68000 and feeding it a 14MHz clock. Kind of like overclocking a Genesis

The text says that you should realize close to a 2x speed up when executing code from FAST RAM (and a lesser speed increase when working out of CHIP RAM). This makes me curious about how this would work in an A2000. Would a 14MHz 68000 have twice the bandwidth to zorroII memory cards? to ROM? Could the same benefits be granted to the A2630 in the processor slot by feeding a 14MHz clock to the 68000 state machine?

It would be nice. Right now the A2630 FAST RAM is about 6x as fast as ROM or zorroII RAM. And of course the A2630 chips are 100ns while the SIMMs on my GVP HC+8 have 60ns chips...

[patrik]

@DamageX:

If you just swap the clock-source the E clock will be double as fast when communicating with the 8520 CIAs, which makes the diskdrive step double as fast, creating problems with trackloaders and if I remember correctly, when you use a terminal-program, the baud rate you select will actually be doubled.

Here is a description of a more proper 14MHz 68000-accelerator which gives correct timings.

These accelerators doesnt increase the bus-bandwidth in any way. The reason that the 68000 benefits from a higher clock is that the 68000 generally spends more time executing functions internally, than it spends reading/writing memory, so there is an noticeable increase in total performance if the time spend executing functions internally is decreased by increasing the clock.


/Patrik

[DamageX]

so there's no bus speed-up afterall, just those ROR.W #8,D0 instructions and the like I guess. thank you