Date   : Mon, 27 Nov 2006 17:01:04 -0000
From   : dl.harper@... (David Harper)
Subject: More sideways RAM questions

BRAHMS wrote:

> Even setting ?&F4 and ?&FE30 will not load stuff into sidways RAM on my
> Beebs, instead I have to poke accross with some assembler I've written.
> Unfortunately the fastest I can get this to work is about 15 seconds
> (instead of *LOAD being about 1!).

While you have set &FE30 (and the RAM copy at &F4) to point to your SW-RAM
you have paged out the filing system ROM. If you use the filing system the
MOS will page it in when necessary, but won't page back your SW-RAM until
the filing system action is completed. This means that if you try to *LOAD
to addresses from &8000 then the filing system will try to write to its own
ROM (and fail, of course).

You will have to do what you require by loading chunks of the file into main
RAM, then writing across to the SW-RAM. You should be able to get it faster
than 15 seconds, though.

I once wrote a small program to this (before I got the Master). I am not
sure where it is, but will look it out if I can and make it available.

The Master, of course, has the command *SRLOAD, but this is actually quite a
lot slower than the straight *LOAD into main memory.

> I'm starting to suspect its because these machines use Watford DDFS?

I don't think so.

> I'd like to know:

> 1) Why does *LOAD not work (it seems to on other machines, I remember
> thats how I used to load my ROMS at school!)

See above. It would not work with the SW-RAM I had either. However the RAM
might have been wired up differently on your school machines so that all
writes went to it (whether it was paged in with &FE30 or not). Alternatively
you might have had a program permanently loaded in the Beeb that redirected
the filing system vectors to make *LOAD work with SW-RAM.

> 2) 8*2kOSGBPB seems to be about as slow as doing 16k*OSBGET - is this
> right?

Should be faster. Perhaps this is the filing system.

> 3) Still no identification on the actual type of RAM.

Can't help here. It sounds very like a thing I had once, but I do not
remember what it was.

> 4) The RAM shows up at slots 14, 12, 6, 2 - are these slots likely to be
> the same RAM duplicated, so far I've not managed to load 2 ROMs at once
> but it could be my dodgy loader!

Are you sure about these? If it was 14, 10, 6, 2 then I could believe it
more easily. There are only 4 SW slots on the standard Model B, and each is
duplicated 4 times.

David Harper