Date   : Tue, 07 Oct 2008 00:36:09 +0100
From   : mfirth@... (Michael Firth)
Subject: New 6502 second processors?

----- Original Message ----- 
From: "Rob" <robert@...>
To: "BBC micro mailing list" <bbc-micro@...>
Sent: Monday, October 06, 2008 10:41 PM
Subject: Re: [BBC-Micro] New 6502 second processors?


> 2008/10/6 Jules Richardson <jules.richardson99@...>:
>>
>> I'm tempted to say that some sort of PC-to-TUBE interface would be 
>> useful,
>> then you could emulate whatever [external] second processor you wanted to 
>> in
>> software[1]. Normally I like messing around with the bare metal (so I'm 
>> not
>> really an emulator fan), but it's not like the second processors have a 
>> lot of
>> external interfaces anyway, so a software approach doesn't lose *that* 
>> much.
>
> Didn't we discuss at some point the potential for emulating various
> other processors on Sprow's ARM co-pro?  I'd have thought that
> emulating a 65C02 in software would be a doddle..  After all, as you
> say, the only interface is the tube...
>
> Rob
>
I would agree that, if emulating the 6502 in software, then the ARM co-pro 
would probably be a better platform than a PC.

Firstly, it already has a Tube interface to the BBC, so that wouldn't need 
to be developed, and (probably more importantly) is isn't already running a 
heavyweight OS, so is likely to have a more consistent performance.

I would still be concerned as to how closely a software emulation would 
match the timing of the real CPU - does Sprow's ARM board have a 
sufficiently fast CPU that it could execute all 6502 instructions faster 
than a 4MHz 65C02 would (and therefore could be made the correct speed with 
suitable NOPs)?

I would also hope that the component parts of a dedicated 6502 Co-Pro would 
be significantly cheaper than for the ARM Co-Pro, so I would hope that the 
end product could be available cheaper too, provided it could be sold in 
enough quantity to offset the up front costs of producing it.

Michael
Michael