Date   : Mon, 18 Jul 1994 23:26:53 +0100
From   : jfid@... (James Fidell)
Subject: Re: Program Request

Chris Rae wrote:

> Does anyone have a program (BBC or PC, I don't really mind) that will 
> disassemble a BBC program to a text file? I'm trying to work out what the 
> OS does and I'd quite like to have it on paper.

I botched my emulator to disassemble 6502 code.  For debugging purposes
I'd already added the ability to display the instruction currently being
executed.  I bodged around with this until it just disassembled the
contents of memory, but it's kind of specific to my implementation.

However, you might be able to do the same sort of thing for your own
implementation.

I do have a disassembler written in BBC BASIC which I could transfer to
UNIX and mail to you somehow, but that would have to wait until next
week.

> Another thing - am I right in assuming that the OS jumps in at address
> &E386 on powerup? I seem to remember this from my Beeb days and
> CA.&E386 seems to reboot the machine... or am I barking up the wrong
> tree again...

I think you're barking up the wrong tree.

On power-up the 6502 loads the contents of the reset vector (held at
0xfffc and 0xfffd) into the PC.  In the case of OS1.2, this is 0xd9cd.
I don't know what it is for earlier operating system releases.

James.

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