Date   : Mon, 22 Aug 1994 13:21:42 +0100
From   : jfid@... (James Fidell)
Subject: Re: general beeb stuff

lamcw wrote:

> 
> "Chris L. Rae" <clr1@...> wrote:
> 
> ;> try zeroing all the paged I/O memory (&FE00 to &FEFF) before running.
> ;> this may help you get the 32K memory up. i find that my emulator
> ;> executes about 270,000 6502 opcodes before the > cursor appears.
> 
> ;I've zeroed the whole of memory, just in case!
> 

I seem to remember that one of the things that the OS does to determine
if it's in a power-up state is to check the contents of the system VIA
IER.  By deduction from the code, I believe that this should be 0x80 on
power-up.  At any other form of reset, it will be some other valuem because
the OS will have enabled at least some of the system VIA interrupts by then.

If all interrupts are disabled, then the OS goes on to clear all memory,
and calculate the amount of memory at the same time, otherwise it checks
the contents of &0258 ( *FX200 :-) to see what should happen.

James.

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