Date   : Fri, 28 May 2004 01:30:09 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Tube / Master Coprocessor question

Sprow <info@...> wrote:
>    Angus Duggan <angus.duggan@...> wrote:
> > Mike Tomlinson writes:
> > >The lower 4 bytes form the actual address; if the upper 2 bytes are FF,
> > >the code is loaded/run in the  I/O processor, if they're 00, it's
> > >loaded/run in the second processor.  Can't recall offhand what values
> > >other than FF or 00 mean, if anything (my AUG's in the loft.)
> 
> > Actually, 0xFFFFxxxx is reserved for the I/O processor.
 
<>&FFxxxxxx - Language memory
  &FFFFxxxx I/O memory
 
and, depending on hardware and filing system:
 
  &FFFExxxx Currently displayed screen memory
  &FFFDxxxx Shadow screen memory
 
> Yup, all the FS APIs set aside 4 bytes for load/exec but some FSs skimp on
> how these are actually stored. For example DFS ran out of space in the
> catalogue so
> 
> > DNFS variants only support 18-bit addresses, rather than store a full 3
> > bytes for each.
> 
> Ahem, 4 bytes.
 
Ahem.  DFS, not DNFS. NFS stores as many bits of the load/exec address as
the fileserver stores. All but the Acorn Level 1 server store a full
32bit address. Not surprising, as the Acorn Level 1 server was a BASIC
program accessing DFS files ;)
 
-- 
J.G.Harston (JGH BBC PD Library) 70 Camm Street, Walkley, SHEFFIELD S6 3TR
jgh@...                - Running on BBCs & Masters with SJ MDFS FileServer
Z80+6502/CoPro+Tubes/Econet+SJ - - - - - - - http://www.mdfs.net/User/JGH/