The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

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Ast A. Moore
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Ast A. Moore » Wed Apr 18, 2018 10:13 am

Joefish wrote:
Wed Apr 18, 2018 10:06 am
There is an alternative . . .
Methinks, kind sir, thou meant to make thy post here. :)
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Joefish » Wed Apr 18, 2018 12:52 pm

Nope, I deliberately set out to undermine all your hard work in this thread. :D
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Ast A. Moore
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Ast A. Moore » Wed Apr 18, 2018 1:07 pm

Joefish wrote:
Wed Apr 18, 2018 12:52 pm
Nope, I deliberately set out to undermine all your hard work in this thread. :D
Oh, ol’ right, then. :P
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by AndyC » Wed Apr 18, 2018 1:21 pm

Nomad wrote:
Wed Apr 18, 2018 6:30 am
One thing that should make everyone uncomfortable..

This is just one un-implemented behavior of a core system. How many more behaviors are left unimplemented by emulators on core/primary systems they are presenting as accurate.

Now consider that many of these same emulators have had continuous development for more than a decade and still do not implement behaviors that are known on core/primary systems?
On the other hand, it's a very tiny detail of emulation for a platform which has a staggeringly accurate level of emulation in multiple emulators. For comparison, I've written a ton of code for the Amstrad GX4000 that has revealed numerous fairly major deviations from what the handful of emulators do. They're slowly getting better but are a long way from being anywhere near as accurate as even the lesser end of the Speccy equivalents.
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Nomad » Wed Apr 18, 2018 1:37 pm

True it depends what you compare it against, I would compare it against something like altirra. One guy in college wrote probably one of the best Atari emulators and what many consider to be one of the best 8-bit emulators while he was in college :lol: The documentation is some of the best I have seen for a emulator but the nicest thing was you could use the program like it was a real system. Even with obscure hardware it emulates it just fine. I couldn't believe it.

But fair enough compared to other systems Spectrum emulators are not so bad - in a much better state than say BBC micro emulators.
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by druellan » Wed Apr 18, 2018 6:37 pm

On Spectrum we always got good emulators IMO. I think part of the problem was the transition from DOS to Windows. A lot of good emulators where left behind during that period. Take for example Ramsoft's RealSpectrum for DOS. I used that emulator to preserve REAL 5 1/4 40 SD Disciple discs, using the PC floppy drive.
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Blerkotron » Wed Apr 18, 2018 7:48 pm

This is fascinating, and very clearly explained - thanks for taking the time, @Ast A. Moore!
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Morkin » Wed Apr 18, 2018 9:43 pm

Nice article on something that's had me a bit perplexed when people have been talking about it.

I think it's a good point you make about the programmers back in the day - it probably wouldn't have been worth their while taking time to implement this with the different model changes, given the tight deadlines everyone seemed to be working under and general craziness (if a lot of the stories are true!).
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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Magnus » Fri Mar 08, 2019 9:07 pm

Thank you for an excellent guide (and the effort to investigate this issue)!

My emulator now handles the +2A/+3 floating bus correctly I think. Here it is running "Woody’s Special" test (epileptics look away ;)):

Image.
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My Spectrum emulator project: https://softspectrum48.weebly.com.

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Re: The Definitive Programmer’s Guide to Using the Floating Bus Trick on the ZX Spectrum

Post by Woodster » Fri Mar 08, 2019 9:32 pm

That looks familiar!
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