RE: Virtual6510 - Can a PC act as a CPU Accelerator?
Date: 2001-12-05 03:36:05

>> Can you explain why I need the synchronisation? I'm interested in
>> understanding if I've missed something here.  Do you mean things like
>> coding, etc?

>Raster effects are one aspect. But more importantly, the serial IEC
>bus requires very strict timing, which I doubt is possible with the
>approach described.

Indeed, and JiffyDOS is even more strict tolerating an error of about 3-4us.
That is why it is proposed these routines are run 100% on the real 6510.
When a kernal call is made to an IEC routine on the virtual engine, it is
trapped and control handed over to the 6510 as a JSR xxxx. Timing done at
1MHz and then RTS brings the virtual engine back into control. That protects
for behaved programs which use the kernal ROM, but not for those that code
their own routines. The SuperCPU as I understand it has the same problem and
you have to flick the 1/20 switch before loads/saves if the program by-pass
the Kernal. 

Through *training* non-kernal calls can also be added to the "1MHz exemption
table". That way a database can be built up from user experiences.

Any other situations?

- Nick


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