Date   : Tue, 23 Aug 1994 12:05:39 +0100
From   : jfid@... (James Fidell)
Subject: Re: Mine did something! Eeek!

"Chris L. Rae" wrote:

> It boots up without a cursor. It comes up with "BBC Computer 16K" (btw I 
> got it to say 32K by filling FD00-FF00 with &80!), then "BASIC", then two 
> LFs.

I'm sure that you only need to make sure that a read of the system VIA
IER returns &80 when the emulator starts.  I do this by initialising all
the VIA registers to zero.  Reading the IER always returns a value with
bit 7 set.

When the OS starts from the reset vector it checks the system VIA IER.
If the lower 7 bits are zero, then it will clear memory and work out
exactly how much memory you have.

I guess the reason that you get 16K is that it isn't doing the memory
check and just uses whatever value is in &028E to decide how much memory
there is.  If this location contains 0, it will assume 16K.  If it's &80
(I think), it will assume 32K.

As long as the hardware has the right initialised values, you shouldn't
need to worry about the contents of memory at all.  I'm not yet emulating
FRED and JIM, and reads from that area will return the ``hidden'' message
in the ROM.

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell