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The SWI system will always have needed some kind of macro wrapper around it in C, generating the correct instruction, because the SWI number was part of the opcode, rather than any kind of value set up in a register. I think, when Acorn introduced the ARM6 or 7, which had a separate data and instruc...

Simply an alternative to a comma, I think; not sure why semicolon is accepted here at all. I think semicolon was the "standard" BASIC syntax for an INPUT command. Certainly MS BASIC expects a semicolon (comma is a syntax error). That's a new one on me. I assume it's a RISC OS feature and if so it m...

Mr Ee and Skirmish. Both great arcade conversions - very easy to get into and a lot of fun.

That was from the 1985 Service Manual, sorry.

Clock signals for the microprocessor are produced by a 16 MHz crystal oscillator (IC43) in conjunction with divider circuitry in part of the video processor (IC6) which produces 8, 4, 2 and 1 MHz signals. The 1 MHz signal coming directly from the video processor is only used for the Teletext genera...

If you've got a Master, try Crazee Rider - self-playing demo mode, plus awesome music!

So it is doing the switching in software, then? However, the BBC Master taught us that there's another way: if you watch the address bus and the CPU's "sync" line, you can know the address code is being executed from. The Master's memory controller uses that to make some code use the currently sele...

It's intentional - it saves the second pass to print them out, and like that you get to see the results as it gets them! Oops, yes, you were right Ed on that. It's a nice speedup! Initially I had the outer loop terminating when P%*P%>=M%, which was causing it omit loads of results; when I added the...

I wonder - is there any other relatively accessible method for listing small primes, other than trial division or a sieve? I think if you can find it, you might be well on your way to proving the Riemann Hypothesis! There are certain things you can say about primes, e.g. every prime is either one m...

Variant on Dave's contribution which uses bits instead of bytes for sieve elements, thus allowing primes up to 100000 to be calculated. Crunched for illegibility speed less slowness. 10L%=25000 20DIMT%7:!T%=&8040201:T%!4=&80402010 30DIMS%L% 40M%=L%*8 50FORI%=0TOL%-1STEP4:S%!I%=0:NEXT 60P%=2:REPEATPR...

You would still expect X=0 or at least that the instruction to known which stack. It feels like it looked useful and as noone else had programmed the 6502 it was a reasonable choice. Shame they didn't extend it in the C02 to (zp) and (zp),x, like they did with store 0. The 65CE02 (as used in the un...

The two GOTOs will be slower than just combining it all into an IF...ELSE IF... ELSE (the former will search from the start of the program looking for the line (I think), while the latter will just search the current line for the token to skip to). I think it's also worth getting rid of any of the "...

Chris recently added "paste from clipboard" into jsbeeb, in case that makes any of this discussion redundant now!

Last time I used (zp, X) was in music playing code, which had to consume no more than a byte from a buffer for each channel, each update. I think if you had to read from ptr+offset for a number of different ptrs, it would be better to copy the address into a known fixed zp pair and use (zp),Y instea...

Often authors just had their own style which they'd "self plagiarise" for want of a better term. For example, here's a Peter Scott "spot the difference": Yoyo http://bbcmicro.co.uk/gameimg/screenshots/Yoyo-TopTen.png The Network http://bbcmicro.co.uk/gameimg/screenshots/Network-TopTen.png Pandemoniu...

Thanks Mark! I think that confirms that this aspect of the hardware was changed in issue 4 then! (along with quite a bunch of other stuff, as I understand it)

Anyone else with an issue 3 (or less), just so we can rule out Chris's machine being a complete freak case?

Incidentally, we'd still love to have any other results from people who are able to try the test! The next thing is to try to figure out why apparently Chris's machine takes longer to respond to the interrupt than an issue 7...

Conclusion to this curious bit of archaeology here.

For anyone wondering what this is all about, this was an attempt to try to prove that Chris's issue 3 BBC B was performing double accesses when writing to the CRTC, but only when the store instruction was aligned with the 1MHz clock. This tale is best read as a continuation of this thread . We know ...

On the Electron, the odd/even fields have different lengths? It would actually be handy if there were any way of distinguishing them on the Beeb, but as far as I know, there isn't.

And loads fine in jsbeeb too!

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

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...

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...

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!...

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...

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!

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...

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...

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...