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Amiga Format CD 10
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amigaformatcd10.iso
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-in_the_mag-
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emulation
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abeeb_beta
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xbeebnote
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1996-11-06
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4KB
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96 lines
> Greetings, Jonathan.
>
> > I'm working on trying to get it to run a decent speed at the moment. The
> > author (James Fidell) says it gets close to BBC Micro speed on a fast 486,
> > but with the '040 being a big endian you have to do a lot of extra
> > shuffling about. Also, Mode 7 update is a little slower that the original
> > xbeeb because of differences between X and Intuition. (I've compiled it on
> > my NetBSD setup to compare, you see 8^)
>
> As regard shuffling, the copyback cache means it can be quicker to access
> bytes by storing and re-reading, than with shifts and rotates. Tables are the
Hmm, I'll have to do some experimenting...the original source used
something along the lines of ((mem[a]) | (mem[a+1] <<8), there may very
well be a quicker way.
> best way to speed things up but bewatre of cache (and possibly even MMU ATU)
Yeah, I've been rewriting bits with lookup tables, the speedups are quite
significant.
> Make sure you write LONG words to Chip RAM. 3640 limits bandwith to chip to
> about 3.5 Mb second, same as an A500 and half that for an A4000/030 or A3000.
> Other accelerators vary between 3.5 and 7 Mb/second. That's the main bottle-
> neck. Word and byte writes to chip go even slower!
Ugh, chip ram bandwidth. I've got a Picasso with CyberGraphX so thankfully
I don't need to worry about that, but I've done a few tests with DblPal and
the differences aren't as great as you might think (using the program
PatchWPA8, ABeeb won't work properly without it).
That's the main complaint that people had about Alien Breed 3D 2,
apparently it uses byte writes to RAM so faster machines don't make the
game run much faster. Thankfully, someone has written a patch to fix this
which apparently makes the game run as fast in 1x1 as the original did in
2x2 8^)
> I've just written a text mode (one byte per character) routine for any Amiga
> that works entirely in custom chips and renders about 115,000 characters per
> second to a bitplane. It supports dynamic fount changes too. Copper use is
> heavy which makes MODE 7 serial attributes tricky (though should be possible)
> as they need precise Copper timing too. It should be possible to use the time
> in other scan lines (9 out of 10) to do the font unpacking and character
> rendering blits, all with beam avoidance. So far my aim is Pet/TRS-80/CPM
> emulation modes.
Blimey, that's quick. Is it system legal?
> > Ariadne? Never heard of that, the only one I know is by James Associates
> > (?) which is BASIC only (ie. no games 8^( ). It is pretty quick, though.
>
> It's the one bundled with the 'Class of the 90s' pack by Commodore. Maybe the
> same as the one you mention, assuming that's 68000-only.
I managed to get it to work on an A1200, I'll have to give it a go again if
I can find it.
> > I've got a few more mods to make for the next version, shall I send it when
> > it's ready?
>
> Yes please. You can skip the games disks for the time being - at least till
> I get the emulator itself working.
Okey dokey, though you shouldn't have too many problems. This isn't the
latest version, it's going to take me a bit longer than I thought to get
that together. I'll send it on when it's ready.
To summarise:
Put the fonts in your FONTS: directory.
Run xbeeb from the CLI with a stack of about 100000 (a guess, I don't know
yet exactly how much it needs).
To change disk, press the 'enter' key on the numeric keypad and navigate
your way to the appropriate directory. (A disk directory always contains a
file called '__CATALOG__'). I have left an empty demonstration 'disk' in
the archive.
More info is given in the file 'readme.amiga'. Tell me when you need the
games 8^)
> > Umm...do you have access to a BBC to obtain the ROMs ? ;^)
>
> Access yes, but haven't managed to get a 5.25" drive working on my A4000 so it
> will have to be trial and error and serial lead fiddling to transfer the data.
You could try the URL http://www.nvg.unit.no/bbc/riproms.html for a legal
way of getting hold of them. Also, you'll need to use the program 'pch' to
enable the xbeeb disk emulation (in the patches directory).
Tell me how you get on,
Regards,
Jon