Re: A2GS Accelerator Thoughts

[doug.cotton@cmdweb.com (Doug Cotton)]

In article <1998071317090500.NAA12653@ladder03.news.aol.com>,
regnirps@aol.com (Regnirps) wrote:

> doug.cotton@cmdweb.com (Doug Cotton)
> Date: Fri, Jul 10, 1998 18:18 EDT
> Message-id: <doug.cotton-ya02408000R1007981718310001@news.earthlink.net>
wrote:
> 
> 
> >Even using some of the fastest processors around (which are VERY
> >EXPENSIVE) you'll be lucky to achieve 40 MHz emulation of the 65816.
> >A 400 MHz processor might get you close, though I suspect you'd be
> >nearer to 30 MHz than 40, and the processor itself will cost hundreds
> >of dollars. I doubt such an approach has much of a chance at being
> >commercially viable.
> 
> The ARM interprets Java at a 2 to 6 instructions per Java byte-code. My own
> experiments show about the same for 6502 or 65816. Thats the full overhead of
> the interpreter included. Since 60 MHz ARM710 style ASICS are available for
> about $20, you should be able to get around 20MHz emulation. 

My estimates came out higher than yours, but I included all the details of
emulating the processor fully. To maintain maximum speed in emulation, ten
seperate engines would be needed to emulate all the various modes of the
65816. I estimated five or six instructions would be required for the
simplest commands, closer to 15 to 20 for complex ones. Some of these may
carry Issue delays due to reuse of resources. In addition, most of the
simple instruction emulations will need to be padded to provide overall
timing characteristics consistant with code execution on a real 65816 (and
to match speeds between the various engines). This also assumes that memory
wasteful techniques are used in the storage of actual 65816 code and data
(8 bits per 32-bit location), otherwise additional delays will be incurred.


Assuming a best-case scenario, I don't think a 60 MHz ARM will do much
better than 10 to 15 MHz emulation, and may possibly do less.

But let's assume for a moment that I'm quite wrong, and a 60 MHz ARM does
deliver 20 MHz 65816 emulation. The ARM costs about double of what a 20 MHz
65816 costs, and the support cost for using the ARM raises the system cost
even further (additional overhead cost in memory to support the engines,
additional wasted memory for 65816 program and data code, higher density
CPLD logic for interfacing to the existing GS System, and probably close to
double the development time/cost).

If you really want to go the emulation route, I'd count on it costing more
for performance equal to a 20 MHz 65816. With that in mind, you might as
well go to a faster and more expensive StrongARM and at least get
additional performance for your extra dollars.

-- 
Doug Cotton <doug.cotton@cmdweb.com>

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