Date   : Fri, 01 Aug 2008 21:06:17 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: ROM type byte for PDP-11

Sprow wrote:
> This leaves 4-7 and 14-15 genuinely free, flip a coin?
 
More or less my line of reasoning, and I have plumped for using 7,
and have added it to the Wiki article.
 
Jules Richardson wrote:
> Jonathan Graham Harston wrote:
> > I have a requirement to specify PDP-11 code in the ROM type
> > byte at rombase+6.
> 
> OK, I'm confusing myself here. We're talking about offset 6 (i.e. the 7th 
> byte) from the start of code in the [Acorn] copro's ROM, right?  Or is 
 
No, not the CoPro's ROM, the start of the code being executed,
which is &8000 when in a ROM slot in the I/O processor, but is
whereever the code has been copied to in the language processor.
Fr'instance, HiBASIC's ROM type byte is at &8006 in the I/O
processor, but at &B806 when executed in the 6502 language
processor.
 
I'm almost at the point where I can boot up Sprow's ARM CoPro
into a PDP-11 environment, and will need a ROM type byte for
PDP-11 ROMs and loaded code.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
PDP-11 BBC BASIC development - http://mdfs.net/PDP11/BBCBasic/blog