Date   : Sun, 13 Jun 2004 11:51:07 +0100
From   : Philip Blundell <pb@...>
Subject: Re: free memory on a model B with Econet?

On Sun, 2004-06-13 at 11:16, Jules Richardson wrote:
> More ponderings... how much free memory can I expect for user programs
> in a BBC B running in mode 2 and hooked up to Econet?

Not a great deal.  NFS will push PAGE up to &1200, and the mode 2 screen
runs from &3000-&7fff.  So you only have the intervening 7680 bytes to
play with, although if you don't plan on using NFS itself (only the
Econet primitive routines) you could reclaim that 1k of filing system
workspace.

> Indeed, what above &400 is needed when not running a language ROM?

You can safely clobber most of this area.  Here's what the Advanced User
Guide has to say about the allocation of these pages.

&200-&2ff OS workspace
&300-&3ff VDU/CFS workspace
&400-&7ff Language workspace
&800-&8ff Sound workspace
&900-&9ff CFS/RS423/speech output buffer
&a00-&aff CFS/RS423 input buffer
&b00-&bff Soft key storage
&c00-&cff Character definitions
&d00-&dff Econet workspace

You will have to leave the page at &D00 alone, since it's required by
the Econet NMI routines.  The page at &200 would also be off limits, but
if you aren't using the VDU system I think most of the rest can safely
be overwritten.

> Other option I suppose is presumably I can jumper the BBC to accept a
> static RAM chip in place of a ROM in the paged ROM area &8000 -  &C000?
> I think I have some 2KB devices spare...

Yes, you can fit a static RAM in place of one of the sideways ROMs;
something like a 62256 is very nearly pin-compatible.  There's no
provision on the motherboard for supplying write enable to these
sockets, but it's easy to pick it up with a flying lead.  

p.