Search found 2448 matches

by BigEd
Sun Apr 21, 2019 6:49 pm
Forum: software: other
Topic: Love Letters (BBC BASIC)
Replies: 3
Views: 152

Re: Love Letters (BBC BASIC)

Hmm, it seems Google's book search is bad for that sort of thing, as the given dates of publications are often very far adrift. I suppose the OED know how to do it!
by BigEd
Sun Apr 21, 2019 4:45 pm
Forum: software: other
Topic: Love Letters (BBC BASIC)
Replies: 3
Views: 152

Re: Love Letters (BBC BASIC)

Very nice. From within a linked article: The magnetic drum was located in a room above the actual computer workshop, which led to introduction of the terms “down transfer” and “up transfer” for these two operations that live on in the modern variants “upload” and “download” - There must be an angel
by BigEd
Sun Apr 21, 2019 12:28 pm
Forum: software: other
Topic: Drawing a circle in BBC BASIC
Replies: 44
Views: 1509

Re: Drawing a circle in BBC BASIC

If you want speed, you almost certainly need to implement something like a Bresenham algorithm. No trig, and maybe even no multiplies either. See the listings posted upthread by lurkio.
lurkio wrote:
Sat Mar 23, 2019 6:48 pm
... from the December 1984 issue of Practical Computing magazine...
by BigEd
Sun Apr 21, 2019 10:22 am
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

And, for completeness, the same routine appears twice in the RISC OS Pico image for the Pi, which apparently contains two versions of BBC Basic: ARM BBC BASIC V (C) Acorn 1989 ARM BBC BASIC VI (C) Acorn 1989 But not quite complete: there's a 65816 Basic for Acorn's Communicator, from 1986. ROMs and ...
by BigEd
Sat Apr 20, 2019 4:54 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

I found this, in AB, which is BBC Basic V for ARM, 1986: 8b10: e5982178 ldr r2, [r8, #376] ; 0x178 8b14: e5d8317c ldrb r3, [r8, #380] ; 0x17c 8b18: e11300a3 tst r3, r3, lsr #1 8b1c: e1b00062 rrxs r0, r2 8b20: e11200a2 tst r2, r2, lsr #1 8b24: e0a11001 adc r1, r1, r1 8b28: e0200602 eor r0, r0, r2, ls...
by BigEd
Fri Apr 19, 2019 8:23 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

I think computer architecture is really interesting - lots of design space to explore, lots of trade-offs. It just happens not to boil down to one number, like how many bits, or how many megahertz.
by BigEd
Fri Apr 19, 2019 4:44 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Ah, yes, so you did! C is rather more intelligible to me, as it happens.
by BigEd
Fri Apr 19, 2019 4:29 am
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

I think this is your code: // Return a pseudo-random integer: unsigned int rnd (void) { unsigned int ecx = *(unsigned char*)(&prand + 1) ; unsigned int edx = prand ; unsigned int eax = edx ; unsigned int carry = (ecx & ~1) | (eax & 1) ; eax = (eax >> 1) | (ecx << 31) ; eax = eax ^ (edx << 12) ; edx ...
by BigEd
Thu Apr 18, 2019 6:29 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

A pretty spectacular saving in cycle count, I'd imagine, too.
by BigEd
Thu Apr 18, 2019 5:25 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

(It's a bit like, if all you can do is add, then you add loads of times. But if you know how to multiply, it's a win. Shifting an LFSR is very like a multiplication by a constant, and we want to shift 32 times. So, if we take the 8th power (basic 4) or the 16th power (basic 4r32) of the thing, we th...
by BigEd
Thu Apr 18, 2019 4:59 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

It's the same polynomial, according to a test like
P.RND(-12345),RND,RND,RND
by BigEd
Thu Apr 18, 2019 4:50 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Ahem, I see I'm running Basic 4 but looking at the disassembly for Basic 4.32 - no wonder my CALL fails! And I can't see exactly the 4.32 code in the 4 ROM, so maybe this was a later change. And indeed, this is the code in Basic 4: 831E A004 ldy #04 8320 6611 f ror 11 8322 A510 lda 10 8324 AA tax 83...
by BigEd
Thu Apr 18, 2019 4:23 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Yes, they are doing something clever: I think you can take the 16th power of the polynomial and apply that twice, which means twiddling more bits, but you're going to touch every byte anyway.
Edit: that said, I tried CALLing the routine and it didn't do as I expected.
by BigEd
Thu Apr 18, 2019 2:45 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Edit: oops! Hmm, I can't quite agree. Both Basic 2 and 4 respond the same way to a negative argument, but the sequence they then produce from that seed differs: PRINT~RND(-12345),RND(99),RND(99),RND(99) Basic 2: FFFFCFC7 82 43 2 Basic 4: FFFFCFC7 30 60 8 Edit: but this is RND(99) not RND. You're qui...
by BigEd
Thu Apr 18, 2019 12:36 pm
Forum: hardware
Topic: How did the Beeb use the /SO pin when selecting ROMs?
Replies: 10
Views: 278

Re: How did the Beeb use the /SO pin when selecting ROMs?

Oh, thanks! It seems the SO output combines two signals, but one of them is DRQ from the FDC chip - used for DMA style transfers. A branch-to-self check on the overflow bit is then the fastest way for the 6502 to wait for the next byte - even faster than the NMI which the Beeb uses.
by BigEd
Thu Apr 18, 2019 12:23 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

Yes, something more like the largest data items which can be acted on by arithmetic and logical operations in single instructions might do it. Trips off the tongue. Although, the IBM 1401 from 1959 then needs special dispensation: When an operation such as addition was performed, the processor began...
by BigEd
Thu Apr 18, 2019 12:17 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 347

Re: What PRNG algorithm's do BBC BASIC's RND functions use

It looks like it's a 33 bit shift register with two taps, acting as an LFSR: see p463 of the BBC Micro Compendium or see p78 of AcornUser025-Aug84 . There was a change in Basic 4, apparently : The random number generator gives different results from previous versions for RND(1) and RND(n). This is t...
by BigEd
Thu Apr 18, 2019 10:24 am
Forum: hardware
Topic: How did the Beeb use the /SO pin when selecting ROMs?
Replies: 10
Views: 278

Re: How did the Beeb use the /SO pin when selecting ROMs?

BTW always interesting to a someone using - or very nearly using - the SO pin. The only use I'm aware of was in Commodore's disk drives.
by BigEd
Thu Apr 18, 2019 10:18 am
Forum: hardware
Topic: How did the Beeb use the /SO pin when selecting ROMs?
Replies: 10
Views: 278

Re: How did the Beeb use the /SO pin when selecting ROMs?

D4 and D5 are not fitted in my issue 4 Beeb... does that help? I see no sign of checking for overflow in JGH's disassembly of OS 0.1 LDX #&03 :\ Start with ROM number 3 .LDCAC STX &0268:STX LFE30 :\ Select ROM LDX #&03 :\ Check four characters LDY &8007 :\ Get (C) offset .LDCB7 LDA &8000,Y:CMP LDFE7...
by BigEd
Thu Apr 18, 2019 9:29 am
Forum: general
Topic: Bit of fun - One change only
Replies: 82
Views: 2515

Re: Bit of fun - One change only

In a recently posted PDF , in an interview with Kenneth Baker, it was said that the government would pay half the price of one computer if schools could pay the rest - so long as they didn't already have one: "It is a very successful scheme and I am very proud of that. Slightly more than 3,000 secon...
by BigEd
Wed Apr 17, 2019 6:55 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

Certainly the ARM has a simple description: 32 bit data bus, 32 bit registers, 32 bit instructions... and as far as I can tell the 8086 through to the 80286 were fairly clearly 16 bits. But as you say, 68k and ns32k muddy the waters a bit, especially as a moderately stable architecture had several r...
by BigEd
Wed Apr 17, 2019 4:17 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

Mmm, it's something I hesitate to comment on because it's the sort of thing which brings out strong opinions! These are, to my mind, actually fuzzy labels and not strict categories at all.
by BigEd
Wed Apr 17, 2019 3:30 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

I notice the 16032 (later renamed the 32016) was described as a 16 bit chip: Hauser is not afraid of Dragons — or for that matter of Spectrums or any other new micros: "None of them is expandable in the same way as the BBC — that market will be adequately dealt with by the Electron". "The BBC is ver...
by BigEd
Wed Apr 17, 2019 3:27 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

p39: How does Acorn intend avoiding these problems with the Electron? "We are now of a size which allows us to pick our subcontractors with care — if they say something will arrive in June you can bet it will. "The chip that we are doing for the Electron is a very much more cautious approach to ULA ...
by BigEd
Tue Apr 16, 2019 8:47 pm
Forum: other vintage computer hardware, software and games
Topic: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)
Replies: 16
Views: 394

Re: YOUR COMPUTER's BBC MICRO REVIEW and the hateful days of type-in listings (VIC20 edition)

Nice short lunar lander type-in there. I see the floppy tape drive is only £175, whereas a teletext decoder for your telly is £200. (Manual for the floppy tape drive here - capacity of up to 63k with access time of 110seconds, or down to 3.5k with access time of 7 seconds.) And I see the chess compu...
by BigEd
Tue Apr 16, 2019 7:56 pm
Forum: general
Topic: Remarkable videos recently posted on Youtube
Replies: 219
Views: 23830

Re: Remarkable videos recently posted on Youtube

From 1985... Another Beeb spotted in a later segment about Revs, demoed by race driver David Hunt, at the time sponsored by Acornsoft, here: https://youtu.be/16NwJwAmbcs?t=21m40s Then a bit with Geoff Crammond talking about writing the simulation. And then a quick mention of Olivetti's takeover of ...
by BigEd
Tue Apr 16, 2019 6:32 pm
Forum: general
Topic: Beeb Spotting
Replies: 61
Views: 5346

Re: Beeb Spotting

16 Beebs used for teaching in Latvia , from 1985: http://www.lumii.lv/uploads/Tehniska1984-1988-1.jpg as noted earlier: Helo again from Kiev. I search Russian spealing Acorn users. I know in Latvia in Riga ste technologicall univercity was teaching class BBC econet Also this thread : http://www.lumi...
by BigEd
Mon Apr 15, 2019 7:08 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 489

Re: Atom Noise Killer @ 2MHz

Excellent!
by BigEd
Sun Apr 14, 2019 7:19 pm
Forum: programming
Topic: Newbie 6502 assembly questions...
Replies: 25
Views: 968

Re: Newbie 6502 assembly questions...

It might help to SEC before shifting or rotating.

Whatever A and C, nine rotates gets you back to where you started. But 8 shifts will clear A, and a ninth shift will clear C too.

Just possibly you'll find this tutorial and in-browser emulator helpful:
http://skilldrick.github.io/easy6502