Date   : Wed, 10 Aug 2005 22:18:23 +0100
From   : Sprow <info@...>
Subject: Re: 80186 co-pro

In article <6.2.1.2.0.20050809232047.02ac4498@...>,
   Rob <robert@...> wrote:

> >[snip- co pro based on WDC 14MHz 6502]
> >
> >If I was to go ahead and design a copro board for this, would anybody
> >else be interested in one?  I'm guessing the cost for a full kit of
> >parts would be somewhere in the region of £35.  There wouldn't be any
> >fine-pitch SMD, so it should be easy to assemble by hand.
>
> 14MHz?  Count me in.  It looks like even a second hand acorn one on ebay 
> will cost me as much, so might as well build a faster one!

Without wanting to paint myself into a corner or do Phil out of any work, I
was planning the following extensions to the ARM copro board proposed earlier

 a) emulate the 6502 tube/65C102 turbo as required in software on the
    ARM. At 75MHz you should be able to at least achieve 10MHz, allowing
    7 ARM instructions to emulate each 6502 opcode
         loop:
         LDRB   opcode,[fakepc],#1
         ADD    PC, PC, opcode LSL#2
         B      opcode0
         B      opcode1
         :
         B      opcode255

         opcode0:
         ; handler
         B      loop

 b) use a soft 6502 blatted into the spare space in the programmable logic
    emulating the Tube IC, I've already done some work on a VHDL core which
    can be downloaded from
         http://www.sprow.co.uk/fpgas/free6502.htm

That way you get two coprocessors for the price of one,
Sprow.