Date   : Mon, 25 Jul 2005 23:28:53 +0100
From   : Rob <robert@...>
Subject: Re: ARM copros, speech cartridges, real timeclocks, etc

At 22:35 25/07/2005, Jules Richardson wrote:

>On Mon, 2005-07-25 at 22:29 +0100, BeebMaster wrote:
> > Multiple second processors /co-processors must have been a possibility
> > in the long distant past as the Master Reference Manual description for the
> > *X command seems to hint this
>
>Well I have a feeling that the Tube was designed to be a bus with
>multiple devices on it, but the reality was that it had trouble coping
>for some reason. I'm just not sure if that was for software reasons or
>some kind of fault with the basic hardware.
>
> >From memory, all the copros have things like bus terminating resistors
>soldered straight to the PCB, as though they weren't meant to be used
>alongside others on the same bus. Yet connecting both a 6502 and Z80
>copro to the same machine doesn't seem like that far-fetched a thing to
>expect people to want to do...
>
>cheers
>
>Jules

I was just contemplating the other day what would happen if I were to 
attach an external second-processor to a Master with a 65C102 already inside..

According to a seriously ancient printout of an article "communicating 
across the tube" I got off Micronet years back, any software running in the 
2P that talks to the host machine has to "claim" the tube for itself before 
transfers go ahead. (Call &0406 with A = &C0+<your sw id> returns carry set 
if you got it.)

The doc implies you're unlikely to be refused unless an interrupt routine 
claimed it first, but I guess this mechanism could also provide a means for 
multiple processors to cooperate on communications with the host too, 
assuming the tube code on the host can accommodate it ...

Rob