Date : Sat, 08 Apr 2000 06:42:47 -0700 (PDT)
From : Thomas Harte <t.harte@...>
Subject: Re: ADFS format tool
Chris Richardson :
> If you want the Electron Welcome disc, visit the 8BS website.
Thanks a lot. I've got that file now, I just need to find a suitable
transfer tool. Oddly enough, on the old 486, fdc doesn't work at all, but
beebdos will happily. Which is good, because the latter will format disks,
it just won't restore / backup disks to image files, but leaves me without
things like a convenient disk->disk single file copy.
F.Haroon :
> Man, get yourself at least a Master to use you disks.
> Why you bother with a ponsy Electron, you'll get tons
> more out of a BBC range of machines. It doesn't
> really make sense to be writing Electron emulator, the
> BBC one will read off the ADFS disks no problem. The
> BASIC is about the same anyway.
All the software I own is Electron software, and while BBC versions remain
unavailable to me (its mostly Acornsoft and Superior stuff), my choice is
either to play the Electron versions or no version at all. But because the
Electron has some intereting timing issues, and the keyboard and sound are
completely different, what does run on a BBC I assume will run at completely
the wrong speed.
Also - from dumping the Electron ROMs, the BASIC ROM is exactly the same as
the one Acorn offer with their BBC emulator. Just wish someone had told me
before hand! Or maybe the Master has a version 3 BASIC or something?
My most compelling reason for sticking with an Electron though is that it
cost me £7, whereas jusging by 8BS, a Master would cost ten times that.
Obviously I'll keep my eyes open if I'm ever at a car boot sale or whatever,
but I'm only a poor student anyway.
That said, the CRTC in BBCs is really good. Once you start fooling it to
reload addresses partway through the frame and so on, you can achieve some
really nice effects with it.
Mike Tomlinson :
> > Would it be worth it?
>
> Um. Would it be worth collaborating with the writer of one of the
> existing BBC-micro emulators to adapt it for the Electron, as this
> could save you a lot of work? Off the top of my head, you'd have
> to chop out the code for mode 7, the 6845 emulation, make major
> changes to the keyboard handler, emulate the special features of
> the Electron's ULA (if you could find docs for it), reduce the
> processing speed to about 10% of that of the BBC... I think my
> brain just blew a fuse.
The thing about the Electron is that, from what I'm aware, the CPU isn't
really any slower. It is just forced to only access RAM when the ULA doesn't
want it, and to communicate with many devices over the 1Mhz bus that are on
the 2Mhz bus on the BBC. So, relative speed changes depending on what the
program ends up doing, and just slowing the CPU down by the average speed
loss across most programs is going to produce the wrong speed for most
stuff!
Besides which, I want to write an emulator from scratch so that I can
incorporate the in-vogue bit-multiplexing and related sort of things that
allow old games to run at higher resolutions and/or bit depths. Therefore,
developing an Electron emulator is a better idea because of the simplicity
of the hardware (less confusion for me), and because games on tape seem to
have been more prevalent than games on disk, leading much more happily to
some sort of snapshot format with the extra information.
Although, of course, I recognise that the operating system ROM is going to
be so scarce that almost no-one will ever be able to use the thing, but as
I'm writing it for my own benefit anyway . . . .
Anyway, once I have a working 6502 and 6522, adding a CRTC and Texas sound
chip and removing the ULA to provide a BBC mode won't be so hard. Especially
not since I've written code to emulate both before! Although the CRTC was
for a CPC emulator, so ran as though it had mangled address lines, so I
can't just reuse it or anything.
What I meant by 'would it be worth it?' is would asking questions here be
worth it when this is principally a BBC Micro mailing list? Obviously I'll
have some generic questions like 'I'm trying to implement loading from tape,
but I don't understand exactly how the bits are encoded' or 'I'm tracing
some test code, and program x seems to be calling osword with undocumented
a=something, whats that meant to be doing?', but is it worth asking 'the
advanced user guide claims interrupt response time is reduced in some modes,
is this just as a result of the CPU being potentially halted when the signal
is generated, or is it possible for the ULA to hold an interrupt signal
up?'?
Thanks for all the responses! Has anyone ever considered trying to establish
a bbc micro usenet group?
-Thomas
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