Date : Fri, 02 Jan 2009 12:44:23 -0000
From : mfirth@... (Michael Firth)
Subject: Master Turbo ROM dump?
Thanks to everyone who posted a link to their copy of the ROM - it looks
like we need an up-to-date central repository for this sort of stuff, as so
many people are now keeping their own copies of things!
I don't think its so much that it overwrites the unneeded ROM with data, as
that the code becomes self-modifying, so that some of the entry points do
different things after the code has initialised.
It seems that all the other copies that people posted were binary-identical,
and worked in BeebEm. Now I can have the fairly pointless vanity of having
the M128 emulation in BeebEm having the 'right' startup banner for the
CoPro!
Does anyone know why it seems that both 6502 Co-Pros have 4K ROMs, but the
first 2K is always blank?
In case anyone is interested, a comparison of the 'grabbed' and 'image'
versions of the ROM is at
http://www.firths.org/bbc/65c102%20ROM%20compare.html. This shows that only
4 bytes are actually different between the two files, apart from the 16
bytes where the I/O access is mapped, which show as FF in the ROM and
various random values in the grab.
Regards.
Michael
----- Original Message -----
From: "Richard Gellman" <splodge@...>
To: <bbc-micro@...>
Sent: Friday, January 02, 2009 12:01 AM
Subject: Re: [BBC-Micro] Master Turbo ROM dump?
> Hi,
>
> There's a reason why a "grab" of the ROM won't work. On startup, the
> TUBE ROM is copied from ROM to RAM (an interesting latch circuit deals
> with this, and gets disabled on the first I/O access). The ROM then does
> some initialisation and then overwrites the unneeded TUBE ROM sections
> with data. Thus, the memory space no longer contains the proper TUBE ROM.
>
> Incidentally, its copied from ROM to RAM to maximise the amount of RAM
> available for applications. You can even completely overwrite the
> provided TUBE routines and supply your own to get more space or maximise
> execution efficiency. I believe Elite does this in the TUBE version.
>
> -- Richard
>
>
> Michael Firth wrote:
>> Does anyone have a working copy of the Master Turbo ROM available online?
>>
>> I found one on the MDFS pages, but I suspect it may have been dumped
>> from a running Turbo (it seems to have values in the I/O space),
>> rather than being a straight dump of the ROM.
>>
>> Certainly, swapping it for the standard 6502 Co-Pro image in BeebEm
>> doesn't work, which I would expect it to, given that I believe the
>> hardware is very similar
>>
>> Thanks
>>
>> Michael
>> ------------------------------------------------------------------------
>>
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