Date   : Thu, 18 Aug 2011 18:50:03 +0200
From   : rick@... (Rick Murray)
Subject: Tube ROM

On 18/08/2011 18:10, Rob wrote:

> And acorn did have the foresight to allow up to 16 ROMs to be used,

I have a FlashROM that I'm going to attempt to wire in as the fifth ROM. 
What with MOS, BASIC, DNFS, and GoMMC, there's not a lot of space left. 
So the fifth ROM will be the Flash with, hopefully, eight images 
available. The only complication is, IIRC, the Flash must be erased at 
one time, however if I ensure a useful filing system (most likely 
Econet) is always available, I can keep the tools and ROM images in 
place to (re)program it in-situ.


> It would have complicated the co-pro startup sequence, though. If you
> have a language ROM in there too, then in what circumstances do you
> want to invoke it?

Very good point.


Another question - the service manual implies that the co-pro startup 
clocks absurdly slowly (something in the order of 350kHz, IIRC?). Is 
this because the ROM is way slow and it is copying the code into the 
faster RAM, prior to switching to full speed for RAM-only execution?


> It would be interesting to hang a 6502 second processor off a ZX
> spectrum, say.

;-) I think the problems are twofold. Firstly, the Tube chip is a 
dedicated specific purpose chip. That's not to say they could not be 
obtained or cloned (a la Kortink), but it may have dissuaded others to 
try. Secondly, and to be rather blunt, I think most other operating 
systems of the era were way too braindead to function as Tube hosts 
without a lot of reworking. Acorn took pains to devise a solid API, and 
one that would work on host and co-pro alike. There's a big expansion 
slot on the back of my Oric (obstensibly for a floppy drive) that might 
be capable of hosting a Tube interface. I think, however, the host 
mechanism would only work if the entire OS was rewritten.

We'd have more luck bunging a Tube chip onto something like a PC or a 
RISC OS machine, something with enough processing grunt to fake the API 
expected. But, then, why bother? BeebEm not only fakes the entire Beeb, 
but the co-pro as well. ;-)


Having said that... a Spectrum with the Sprow's ARM co-pro. That would 
be a mind-screw of epic proportions.
   [ http://tvtropes.org/pmwiki/pmwiki.php/Main/MindScrew ]


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...