Date : Fri, 12 Sep 2003 10:23:49 +0100 (BST)
From : BBC Micro <b_b_c_m_i_c_r_o@...>
Subject: Re: Best Documentation on Rom Format
Thanks for your help, the rom was exactly as you
described and was straightforward to understand:
I followed the jump at &8003 and it checked for the
OSCLI code 4 and then took me to a lookup table for
the roms commands and I was able to investigate the
particular commands I was interested in. These
commands were in assembler.
I didn't find out what the Basic code was about (as I
didn't look into the other commands) but there seemed
to be about 5 fragments, each terminated with bytes
"0D FF". Maybe it was for reasons the second poster
described.
Cheers!
--- Andrew Hancock
<Andrew.Hancock@...> wrote: >
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> Ben
>
> I wrote a program for the BBC Micro/Master years
> ago, which encoded basic
> programs to run in Sideways RAM/ROM, that could then
> be run with the
> *COMMANDS.
>
> Not strictly RFS, as this is just life the Tape
> Filing System but within
> ROM.
>
> - From memory, we could have used RFS, but didn't
> want users access to the
> Basic/Assembler Programs, that they could have
> LOADed"" or CHAINed"".
>
> So we encoded/stored them into RAM/ROM, used
> *COMMANDS to execute and LOAD
> and RUN the programs, and used various other tricks
> to clear memory upon
> CTRL-Break/Escape/Break etc. So users couldn't get
> at the basic/assembler
> code.
>
> Seems a bit OTT now. Some time this year, I said
> this last year when I get
> the time, I need to get the BBC Development Stuff
> out of Stores and have a
> look at it.
>
> Regards
>
> Andrew
>
>
>
>
> - -----Original Message-----
> From: Brian Widdas [mailto:brian@...]
> Sent: 10 September 2003 16:14
> To: BBC Micro
> Cc: bbc-micro@...
> Subject: Re: [BBC-Micro] Best Documentation on Rom
> Format
>
>
> On Wed, 10 Sep 2003, [iso-8859-1] BBC Micro wrote:
>
> > What is the best documentation that I can get from
> the
> > web regarding the layout of BBC B rom images?
> >
> > The Problem:-
> >
> > I have a rom image that seems to contain basic
> code as
> > well as machine code. I want to find where the
> code
> > associated with each of the roms star commands is.
> I
> > can dissasemble with Exmon II so thats no problem.
>
> The three bytes at &8003 (offset of 3 bytes into the
> ROM) will (most
> likely) contain a JMP instruction to an address
> further within the ROM.
> The code here is for handling service requests to
> ROMs, and should do
> something along the lines of checking for the
> service code which indicates
> an unknown OSCLI command (I think it might be 4, but
> I could be wrong).
> Most likely, you'll find some kind of lookup table
> of OSCLI commands to
> addresses, but it's impossible to say what it'll
> look like as it's up to
> the individual ROM programmer as to how they write
> it.
>
> As it contains BASIC code, an alternative
> possibility is that it's a ROM
> Filing System (RFS) ROM. An RFS ROM is basically a
> small ROM header and
> service call handler which points to a block of ROM
> containing files,
> encoded in the same way as Cassette Filing System
> data (yes, really,
> blocks, headers and CRCs included...). Try going
> into RFS (I /think/ it's
> *ROM, but CTRL+R+BREAK will also do it) and typing
> *CAT
>
> Brian
> - --
> brian@...> fortune
> You are wise, witty, and wonderful, but you spend
> too much time reading
> this sort of trash.
>
>
>
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