Search found 226 matches

by crj
Sun Nov 19, 2017 7:38 pm
Forum: off-topic
Topic: LOLPRICE
Replies: 2666
Views: 178102

Re: LOLPRICE

Still, gotta try it on I suppose! You think that's bad? A previous employer discovered one of its brochures being sold on eBay. It was only two years old, and naturally we'd given them away at the time. We rummaged in a cupboard and found several dozen more, in pristine condition. We briefly contem...
by crj
Sun Nov 19, 2017 2:58 am
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

It's explicit about a lot of things, yes. Though unless I've missed something major it's entirely silent on any kind of approved way to access more than 64K of I/O space? While in theory you could map 32K by taking the entire upper half of JIM that does strike me as a tiny bit antisocial. Is there a...
by crj
Sat Nov 18, 2017 11:54 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

DC/etc are implemented as per the Acorn intent, &FCFF for the 256-byte page within a bank of 64K, with &FCFE and lower if implemented select what bank of 64K, etc. as in BeebEx.gif which implements a 16M address range with two latches. Is there any clear documentation of exactly what Acorn'...
by crj
Sat Nov 18, 2017 11:43 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

RAM expanders would then only need take up either one page in the JIM 64k map and have their own paging registers in FRED or two pages in JIM with their RAM accessed in one page and their control registers in a second JIM page. Actually, if you're trying to address much more RAM than can sensibly b...
by crj
Sat Nov 18, 2017 11:28 pm
Forum: upcoming and recent events & exhibitions
Topic: Hard problems @ ROUGOL / Mon 20th Nov 2017
Replies: 5
Views: 123

Re: Hard problems @ ROUGOL / Mon 20th Nov 2017

helpful wrote:juggling


Aha. I was already wondering, but that makes it extraordinarily likely it's the same Colin Wright I knew a long, long time ago in an entirely non-Acorn-related context. It's a small world. (-8
by crj
Fri Nov 17, 2017 5:45 pm
Forum: wanted
Topic: Wanted: CUB Microvitec Monitor
Replies: 1
Views: 48

Re: Wanted: CUB Microvitec Monitor

Looks like you and the author of a certain other recent thread should talk to one another. (-8
by crj
Fri Nov 17, 2017 5:39 pm
Forum: wanted
Topic: WTB: 5.25" Floppies
Replies: 15
Views: 198

Re: WTB: 5.25" Floppies

My head aches with all the info I'm trying to remember, it's sad really, back in the 80's I could write a rom header and the software following it without a single reference to data and now all I remember on that front is the first two instructions, jumps to language and service. I seem to have the...
by crj
Thu Nov 16, 2017 11:40 pm
Forum: software: classic games
Topic: "Unfixable bug" in BBC B Elite
Replies: 54
Views: 2991

Re: "Unfixable bug" in BBC B Elite

My own take on this kind of thing is that it ought to be legal to use copyrighted material if the copyright owners haven't exploited that copyright in five years. If they begin exploiting their copyright again, use should remain legal for five years, with new uses permitted for the first year (so th...
by crj
Thu Nov 16, 2017 8:22 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

Hmm. That fails if there's actually a second processor present, though. And there's no way I'm seeing of preventing the second processor from initialising. Annoyingly, I see nowhere universally safe to stick the code, then: PAGE on a machine with lots of filing systems is higher than HIMEM on an Mod...
by crj
Thu Nov 16, 2017 7:59 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

It feels deeply inelegant to me that only one device on the 1MHz bus can use that mechanism. If they'd intended it for anything other than test hardware, I'm guessing they'd have kept running through JIM pages, starting at &00, doing JMP (&FDFE) on any page where &FDFF contained &FD,...
by crj
Thu Nov 16, 2017 6:53 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

Gosh. I never knew that!

I can't help thinking a simple 8K EPROM for a Sideways ROM socket must have been a lot cheaper than the logic they needed to make that hack play nice on the 1MHz bus, though...
by crj
Thu Nov 16, 2017 6:51 pm
Forum: hardware
Topic: Torch Graduate
Replies: 18
Views: 1253

Re: Torch Graduate

Intriguing!

Does anyone know which range of OSes support that?
by crj
Thu Nov 16, 2017 5:38 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

That's certainly not how I'd design a ram disk. Note that LDA &abcd is one cycle quicker than LDA &abcd,X so it's actually more efficient to present a series of bytes through consecutive reads of one I/O location than as a page! You only want to be using JIM if genuine random access to an I/...
by crj
Thu Nov 16, 2017 5:32 pm
Forum: hardware
Topic: Moulds?
Replies: 1
Views: 95

Moulds?

Bizarre random thought of the day: people have investigated what's happened to the Acorn name, the copyright, the source code for various things... ...but what ever happened to all the injection-moulding moulds? I bet they got scrapped, alas. If someone somewhere did still have the "wedge"...
by crj
Thu Nov 16, 2017 5:17 pm
Forum: hardware
Topic: read / write to JIM
Replies: 28
Views: 507

Re: read / write to JIM

JIM really isn't for general-purpose RAM! Quite apart from anything else, it's half the speed of sideways RAM; why not use sideways RAM instead? It's really intended for two things, one rather more niche than the other. The first is removing the CPU card from an Acorn System and instead exposing its...
by crj
Thu Nov 16, 2017 5:05 pm
Forum: software: classic games
Topic: Legacy of the BBC Micro User magazine / Database Publications Ltd
Replies: 12
Views: 600

Re: Legacy of the BBC Micro User magazine / Database Publications Ltd

Ah yes. I remember the days of manual paste-up!

But hey, paying by the column-inch is at least better than paying by the word. It doesn't discourage the use of long words.
by crj
Thu Nov 16, 2017 3:51 am
Forum: projects
Topic: Starting a Prince of Persia port...
Replies: 129
Views: 7867

Re: Starting a Prince of Persia port...

Note, incidentally, that this is almost equivalent to triple-buffering. At any given moment, you have access to what's on screen, the background without any foreground sprites, and what's going to be on screen next frame.
by crj
Thu Nov 16, 2017 3:10 am
Forum: projects
Topic: Starting a Prince of Persia port...
Replies: 129
Views: 7867

Re: Starting a Prince of Persia port...

The challenge I have is that to reduce flicker I need to restore, store & plot the player (moving) sprites as quickly as possible, so in a localised manner, rather than doing everything in passes. To do this I would need to flag all plot operations that overlap the bounding box of the moving sp...
by crj
Wed Nov 15, 2017 12:46 am
Forum: off-topic
Topic: LOLPRICE
Replies: 2666
Views: 178102

Re: LOLPRICE

Boydie wrote:Do I need to increase my home insurance?

You jest, but...

Domestic insurance policies tend to offer new-for-old replacement on electronics. I'm far from clear how that interacts with retrocomputing.
by crj
Wed Nov 15, 2017 12:39 am
Forum: programming
Topic: 6502 Stack
Replies: 8
Views: 289

Re: 6502 Stack

However, what goes on the stack must come off, and each PLA takes 4 cycles. (Using TSX,TXA,ADC#,TAX,TXS to discard any number of items at once takes 10 cycles.) You need to be using the data on the stack enough times that saving one cycle each time you LDA &101,X instead of LDA (&70),X is a ...
by crj
Tue Nov 14, 2017 8:42 pm
Forum: programming
Topic: 6502 Stack
Replies: 8
Views: 289

Re: 6502 Stack

In that case, you'll have two different entry points, one for the ROM and one for the executable. Can't the entry point just pass the origin to the decompressor in a register?
by crj
Tue Nov 14, 2017 8:35 pm
Forum: projects
Topic: Starting a Prince of Persia port...
Replies: 129
Views: 7867

Re: Starting a Prince of Persia port...

all my investigations and experiments feel like I'm fighting the original architecture of the code, which is set up to be double buffered OK. Having put on my 8-bit Acorn hacker hat and suggested tricks for scavenging more RAM from the Master, I'll now take it off and instead put on my computer sci...
by crj
Tue Nov 14, 2017 4:18 pm
Forum: projects
Topic: Starting a Prince of Persia port...
Replies: 129
Views: 7867

Re: Starting a Prince of Persia port...

If there really is no way to make the code more compact and it really is only 2K you need, you could just shrink MODE 2 by a little instead of resorting to MODE 5? Shaving 32 pixels off the bottom would give you 2560 bytes. Or you could shave just 16 pixels and have 1280 bytes in each of main and sh...
by crj
Tue Nov 14, 2017 4:05 pm
Forum: programming
Topic: 6502 Stack
Replies: 8
Views: 289

Re: 6502 Stack

Curiously, I was independently thinking similar thoughts just the other day. It occurred to me that if you wrote a fragment that stored PLA:TAX:PLA:TAY:PHA:TXA:PHA:RTS somewhere in memory then JSRed to it, on return you would have the address of your code in X,Y. It would be faff, but with care that...
by crj
Sun Nov 12, 2017 11:09 pm
Forum: software: other
Topic: Tree of Knowledge loading programs
Replies: 6
Views: 204

Re: Tree of Knowledge loading programs

FORI%=0TO&400STEP4:I%!&7C00=I%!TOP:NEXT What that does is copy a kilobyte (&400 bytes) from immediately above the program into screen memory. A BBC BASIC program has a terminator at the end of it. Normally - and certainly when you SAVE - that will be the last thing before the end of the...
by crj
Sat Nov 11, 2017 10:43 pm
Forum: hardware
Topic: Trojan Room Coffee Pot
Replies: 8
Views: 261

Re: Trojan Room Coffee Pot

Quentin's still in circulation so anyone sufficiently motivated can ask him. I heard the details of the coffee pot in the early nineties and my recollection may be flawed, but I think that when the Wikipedia article refers to "a video capture card" they're hiding some of the baroque horror...
by crj
Sat Nov 11, 2017 2:22 pm
Forum: upcoming and recent events & exhibitions
Topic: ABUG EAST MIDLANDS (Winter Warmer) 17-19 November 2017 (Leicestershire) BOOKING THREAD
Replies: 124
Views: 3578

Re: ABUG EAST MIDLANDS (Winter Warmer) 17-19 November 2017 (Leicestershire) BOOKING THREAD

Arcadian wrote:I'm sure DaveH would contest that there's no such thing as an Elk mobo that can't be repaired!!

See also: the Ship of Theseus :-p
by crj
Sat Nov 11, 2017 2:16 pm
Forum: hardware
Topic: Master ADFS problems
Replies: 12
Views: 285

Re: Master ADFS problems

Is it possible you have a single-sided disc drive? An 80-track Master 128 Welcome disc has all the data on the "second" side of the disc which can't be read by a single sided drive. The 40-track version uses the "first" side. It's the same disc, but there is a utility on the dis...
by crj
Sat Nov 11, 2017 2:12 pm
Forum: hardware
Topic: Master ADFS problems
Replies: 12
Views: 285

Re: Master ADFS problems

I'm not sure how to tell if the drive is single sided. It has CUMANA written on the front, and a couple of switches at the back that can change between 40 and 80 track modes. With DFS, try to use drives 2/3. Those are the flip sides of drives 0/1 in DFS. Meanwhile, if you have a 40/80 switch, try t...
by crj
Sat Nov 11, 2017 2:03 pm
Forum: software: classic games
Topic: "Unfixable bug" in BBC B Elite
Replies: 54
Views: 2991

Re: "Unfixable bug" in BBC B Elite

Acorn didn't use anything but the 8271 anyway until the B+ (and that still was only in single density) They offered a 1770 board for the Model B. The copyright date on its installation instructions is 1985, so it's not clear if it came before or after the B+'s launch. Also, there was the Electron P...

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