Date   : Sun, 19 Apr 2009 22:51:39 +0100
From   : mfirth@... (Michael Firth)
Subject: Easter Disaster

----- Original Message ----- 
From: "Mark Haysman" <jumbos.bazzar@...>
To: <bbc-micro@...>
Sent: Sunday, April 19, 2009 8:39 PM
Subject: Re: [BBC-Micro] Easter Disaster


>>  I wonder whether the 1.2 OS would work in a real Master.  It might be
>> useful to run non Master-compatible software.
>
> "Calling Mr. Firth to the stand!"......... :-)
>
Here sir! :-)

Tests so far seem to say that most things work, but that the ADC and FDC 
chips
will require patches to the OS and FS ROMs respectively, as they are at 
different
locations in the Master memory map than the BBC B/B+ one.

This means that if you only want to access TAPE, ROM or HDD / CF ADFS files,
(and possibly GoMMC, I've not got one to investigate), and don't need the 
ADC
to work, then things should be fine.

One of my background projects is to patch a 2.2x DFS and/or the 1.30 ADFS to
work with the Master addressed FDC. If it was just locations changing then 
the patch
would be simple, but the re-locating of the bits in the FDC control register 
make things
a bit more fiddly - one obvious problem is that the ADFS 1.30 ROM doesn't 
have enough
spare bytes to accommodate a control register re-shuffling routine, so 
either some ROM
bank switching is needed, the reshuffling routine needs to go in RAM 
somewhere (which
screws up the games compatibility this would be useful for), or a bigger 
overhaul of the ADFS
ROM would be needed.

I guess the other approach would be to work backwards from the ADFS 1.50 
ROM, and
convert the FS memory request and use code to use the BBC main memory ROM 
calls and
locations, rather than the Master FS RAM space, but I haven't looked into 
this.

One day I'll find some time to blow a ROM chip for my real master too - 
currently I've just
been playing with BeebEm to find out what's possible easily.

Regards

Michael