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by Rich Talbot-Watkins
Wed Sep 18, 2019 8:06 pm
Forum: software: classic games
Topic: Nightshade protection [technical]
Replies: 168
Views: 54382

Re: Nightshade protection [technical]

And loads fine in jsbeeb too!
by Rich Talbot-Watkins
Wed Sep 18, 2019 5:37 pm
Forum: software: classic games
Topic: Nightshade protection [technical]
Replies: 168
Views: 54382

Re: Nightshade protection [technical]

acorn wrote:
Wed Sep 18, 2019 5:32 pm
Is this tape still available somewhere? The whole site went out of existence ...or at least seems to have changed purpose.
It's been reuploaded here a few times I think, and here's one of them!
viewtopic.php?t=5023#p86170
by Rich Talbot-Watkins
Wed Sep 18, 2019 4:30 pm
Forum: software: classic games
Topic: Game software protection list ( Kevin Edwards )
Replies: 32
Views: 791

Re: Game software protection list ( Kevin Edwards )

Then you just have to consider the decryption step (for which you have the code, unencrypted) part of the loading process. As long as you call the decryption routine once, probably before saving but maybe after reloading, you should be good to go. I suppose if the last chunk of code loaded from the...
by Rich Talbot-Watkins
Sun Sep 15, 2019 8:03 pm
Forum: software: classic games
Topic: Game software protection list ( Kevin Edwards )
Replies: 32
Views: 791

Re: Game software protection list ( Kevin Edwards )

Yeah, we talked about Star Clash once before on here. I personally doubt that it shared any code in common with Elite, because it runs at a much worse frame rate and the ships are far more simplistic. But clearly the look and feel of the game is very much 'inspired' by Elite, and it got withdrawn fr...
by Rich Talbot-Watkins
Sun Sep 15, 2019 7:34 pm
Forum: software: classic games
Topic: Game software protection list ( Kevin Edwards )
Replies: 32
Views: 791

Re: Game software protection list ( Kevin Edwards )

BBC Micro only Stryker's Run How did you deal with stuff like Stryker's Run which had to be compatible with more than just OS 1.20? You couldn't have used your 'nasty' protections from Ultimate I guess, but I did notice the Kevin Edwards signature lock-up where it spends 4 seconds decrypting stuff!...
by Rich Talbot-Watkins
Sun Sep 15, 2019 7:22 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

In the case of a '2MHzE even' clock shape, it does look like there's a falling edge on 1MHzE a full cycle before time Q, and yes, I would expect the 6502 and glue logic to have done all the necessary things by this time. (I say that without having studied the schematic.) Is this what's being allude...
by Rich Talbot-Watkins
Sun Sep 15, 2019 4:11 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

Ah, yeah. And I see it in the circuit diagram now as well.

Do you think there's any possibility it might be happening on the 1MHz cycle before Q, or is that too premature for the CPU to have set things up?

Thanks for your expertise!
by Rich Talbot-Watkins
Sun Sep 15, 2019 3:56 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

There are two cases for the clock crossing. Only one is shown in the NAUG (and App note 3). The other one is the low phase of the 2MHzE is 250ns and high phase is 750ns (75% duty cycle). The falling edge of 1MHzE and 2MHzE always coincide. Writes from CPU -> device latch at this falling edge. The C...
by Rich Talbot-Watkins
Sun Sep 15, 2019 3:14 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

I'd always thought it was just the high clock period (T...U here) that got stretched, as per Matt's jsbeeb article: https://xania.org/201405/jsbeeb-getting-the-timings-right-cpu - but this diagram appears to show the low clock period stretched too! Unfortunately I don't have the skills to figure ou...
by Rich Talbot-Watkins
Sun Sep 15, 2019 2:45 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

Even better, if anyone can see with a scope what's going on with the 6502 A15, phi1, phi2 and R/W pins, and with the 6845 CLK, R/W, E and /CS pins while this program runs, that'd be amazing information! 10 MODE 0:REM high clock mode 20 P%=&900:[OPT2:SEI:.loop LDA #0:STA &FE00:LDA #80:STA &FE01:JMP l...
by Rich Talbot-Watkins
Sun Sep 15, 2019 2:27 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

Re: CRTC timing with 2MHz clock

That's not exactly my understanding of it. This diagram from the AUG http://forum.6502.org/download/file.php?id=1523&sid=cd810fa2d59407c2b4e2005f7795a7df&mode=view shows that it's not switching in the 1MHz clock so much as actually stretching one cycle over three. It is certainly deterministic; if y...
by Rich Talbot-Watkins
Sun Sep 15, 2019 2:07 pm
Forum: hardware
Topic: CRTC timing with 2MHz clock
Replies: 14
Views: 296

CRTC timing with 2MHz clock

Throwing a question out there to anyone who understands this hardwarey stuff more than I do. The 6845 CRTC can operate on the Beeb at two clock speeds - 1MHz and 2MHz - according to bit 4 of the Video ULA. I assume this controls not just its character clock rate, but also the rate at which its regis...
by Rich Talbot-Watkins
Sat Sep 07, 2019 11:37 am
Forum: programming
Topic: Determining Graphics Modes
Replies: 6
Views: 295

Re: Determining Graphics Modes

OSBYTE 160,96 returns the colour mask - the maximum number of colours minus 1 (which will be zero for MODE 7). Although that's also reading a VDU variable, so that's as tied to an Acorn 8-bit platform as reading the current mode via VDU variable &55. On RISC OS you'd do it via SWI OS_ReadModeVariab...
by Rich Talbot-Watkins
Fri Sep 06, 2019 1:50 pm
Forum: programming
Topic: Row multiplication table substitution
Replies: 13
Views: 344

Re: Row multiplication table substitution

If you're interested in a challenge/mystery, perhaps you could look at why the original Battletank release (e.g. the tape version here ) didn't work on a Master. I never figured it out - it just gets to the title page and then hangs when you press fire to start. The disk version works OK, and I assu...
by Rich Talbot-Watkins
Fri Sep 06, 2019 9:51 am
Forum: programming
Topic: Row multiplication table substitution
Replies: 13
Views: 344

Re: Row multiplication table substitution

That's just what I did earlier, thanks, as well as trapping screen clears. You have a good memory as there was also an IRQV restore to fix. Some of those are perverse: they sometimes go to the trouble of saving the old vector as an exit point but don't use those values to do any restoration, prefer...
by Rich Talbot-Watkins
Thu Sep 05, 2019 12:02 pm
Forum: emulators
Topic: BBC B hardware mapping extent -- quick tests!
Replies: 15
Views: 401

Re: BBC B hardware mapping extent -- quick tests!

Note also the inputs to IC23 which determine which of the 32 byte blocks of SHEILA get cycle stretched access!
by Rich Talbot-Watkins
Wed Sep 04, 2019 12:08 pm
Forum: programming
Topic: Row multiplication table substitution
Replies: 13
Views: 344

Re: Row multiplication table substitution

Thanks for the confirmation. Coincidentally it was Contraption that I was looking at. Unfortunately the Master zero page locations don't seem to be comprehensively documented anywhere that I can see. The MRF(1) only lists D0-FF as MOS workspace (as does the ARM). The NAUG gives the usual Model B de...
by Rich Talbot-Watkins
Wed Sep 04, 2019 12:03 pm
Forum: emulators
Topic: BBC B hardware mapping extent -- quick tests!
Replies: 15
Views: 401

Re: BBC B hardware mapping extent -- quick tests!

scarybeasts wrote:
Wed Sep 04, 2019 9:40 am
?&FE2F=0
?&FE24=0
?&FE20=0
If you're aiming to hit the Video ULA control register and not the palette, that first one should be ?&FE2E=0.
by Rich Talbot-Watkins
Tue Sep 03, 2019 10:00 pm
Forum: programming
Topic: Row multiplication table substitution
Replies: 13
Views: 344

Re: Row multiplication table substitution

No, the Master doesn't use a table - it just has the row multiplication hard coded - so there's nothing you can do unfortunately. I remember this exact problem with the game Contraption, and the only viable patch was to actually change all the VDU 31 OSWRCH calls to position the cursor at the right ...
by Rich Talbot-Watkins
Wed Aug 21, 2019 7:30 pm
Forum: other vintage computer hardware, software and games
Topic: Early 70s Calculators
Replies: 52
Views: 4888

Re: Early 70s Calculators

What's up with that Sinclair Scientific exactly?

http://files.righto.com/calculator/sinc ... lator.html

3.1415
cos
9.9546 10
??
by Rich Talbot-Watkins
Wed Aug 21, 2019 6:46 pm
Forum: programming
Topic: Detecting available file systems
Replies: 17
Views: 765

Re: Detecting available file systems

Quick look at the datasheet, and it seems like the 8271 can return "Drive Not Ready" if the drive is not powered up, the disk is not loaded or a non-existent drive is accessed. So no idea why Acorn's DFS doesn't respond to it.
by Rich Talbot-Watkins
Wed Aug 21, 2019 12:12 pm
Forum: programming
Topic: Detecting available file systems
Replies: 17
Views: 765

Re: Detecting available file systems

for some reason the 8 bit filling systems never seem to have a timeout and will just sit waiting forever. Actually, that's something I've never really thought about. If you send the 8271 a command when there's no disk in the drive, will it return an error result, or will it just stall and wait for ...
by Rich Talbot-Watkins
Tue Aug 20, 2019 11:07 am
Forum: programming
Topic: Detecting available file systems
Replies: 17
Views: 765

Re: Detecting available file systems

That's part of the psychic abilities. How does the person writing the program know that there's a filing system number 73 which is selected with the *ZEEBAR command, but must be selected with the *XEBURE command to prevent it attempting to electrocute nearby cats on selection? How did that get out ...
by Rich Talbot-Watkins
Tue Aug 20, 2019 6:29 am
Forum: emulators
Topic: Emulation tests
Replies: 13
Views: 572

Re: Emulation tests

?&257 non-zero means output is being spooled, so I guess you can just check that in an OSWRCH trap. I agree that this is surely the neatest and most automatic way of capturing test results.
by Rich Talbot-Watkins
Mon Aug 19, 2019 4:42 pm
Forum: emulators
Topic: Emulation tests
Replies: 13
Views: 572

Re: Emulation tests

Don't really see the problem with hooking OSWRCH to be honest. It means you can write a perfectly normal test on real hardware (and display the results), and then run the same thing on an emulator and capture the results (and compare with your ground truth). Most of the tests we have are BASIC snipp...
by Rich Talbot-Watkins
Mon Aug 19, 2019 8:25 am
Forum: emulators
Topic: Emulation tests
Replies: 13
Views: 572

Re: Emulation tests

Can you not create a 'test' variant of your 6502 emulation which traps PC=&FFEE and records the accumulator on each call? This is the approach I'd take in any case.
by Rich Talbot-Watkins
Wed Aug 14, 2019 12:16 pm
Forum: programming
Topic: !GCC on RISC OS with -O2 and cexpf
Replies: 5
Views: 154

Re: !GCC on RISC OS with -O2 and cexpf

Thanks for the advice. I was intending to optimise going forward, using look up tables and fixed point arithmetic to replace the floating point code. Even divide and multiply makes me worry when I'm updating thousands of vertices each frame! Yeah, exactly. You can't get around divide when doing per...
by Rich Talbot-Watkins
Wed Aug 14, 2019 11:40 am
Forum: programming
Topic: !GCC on RISC OS with -O2 and cexpf
Replies: 5
Views: 154

Re: !GCC on RISC OS with -O2 and cexpf

I would highly recommend for performance that you use fixed point representation for your matrix maths, and use a sine table to lookup sines/cosines rather than calculating them with sinf()/cosf(). Also, remember there are some nice trig identities you can use to avoid multiplications: e.g. sin A * ...
by Rich Talbot-Watkins
Sun Aug 11, 2019 9:50 pm
Forum: software: classic games
Topic: Exile - early port
Replies: 3
Views: 417

Re: Exile - early port

Looks much nicer graphically than the version which eventually arrived for the C64! Thanks for that!
by Rich Talbot-Watkins
Fri Aug 09, 2019 4:21 pm
Forum: general
Topic: Disc or Disk. Silly-Season debate.
Replies: 93
Views: 1521

Re: Disc or Disk. Silly-Season debate.

Elminster wrote:
Fri Aug 09, 2019 4:13 pm
They probably dropped the 'u' to save printing costs :)
Nonsense, everyone knows that the correct spelling is coloueur.