Search found 522 matches

by Diminished
Sun Sep 06, 2020 6:29 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Incidentally, one mystery I'd like to solve is how 2 byte opcodes are described. There doesn't seem to be much of a pattern in that, and I imagine that, of all those signals, some of them will be OR'd together to specify 2 byte opcodes. (I guess the signal is then latched, and causes the subsequent...
by Diminished
Sun Sep 06, 2020 3:02 pm
Forum: 8-bit acorn software: classic games
Topic: BBC Elite source, now fully documented and explained
Replies: 75
Views: 3210

Re: BBC Elite source, now fully documented and explained

MarkMoxon wrote:
Sat Sep 05, 2020 9:41 pm
I wonder if some of the other versions do need to be at full pitch to trigger the onslaught?
I believe the original DOS version worked this way (which is the one that I played through BITD), but it's been a long time.
by Diminished
Sun Sep 06, 2020 2:43 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Here's the left-hand decode table, modulo any errors I made. left_instruction_table.jpg I may have been the last to spot these things, but anyway: There are 41 columns. The marketing document claims 46 instructions; it's not a million miles away. Bit 7 and 6 row pairs appear to work as exact complem...
by Diminished
Sun Sep 06, 2020 1:07 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

The bit ordering into the PLA looks to be the same as it is everywhere else. Which is both good, and bad.

The 8273 ROMs will hopefully help, although maybe we'll have to wait another week for those.
by Diminished
Sat Sep 05, 2020 11:45 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

This is as expected I think.
same_different.jpg
The chip isn't quite the same as the 8271 though! There are differences here and there.
by Diminished
Fri Sep 04, 2020 11:26 pm
Forum: 8-bit acorn software: classic games
Topic: BBC Elite source, now fully documented and explained
Replies: 75
Views: 3210

Re: BBC Elite source, now fully documented and explained

And yet they're still stupid enough to sell you more missiles.
by Diminished
Fri Sep 04, 2020 10:29 pm
Forum: 8-bit acorn hardware
Topic: Identification required please
Replies: 9
Views: 348

Re: Identification required please

Yeah, it looks like our original A, which I no longer have. Some very early models (including ours) had practically everything socketed, presumably because they were waiting for parts. I guess when they arrived they could just whack everything in the sockets in a few minutes and ship. On at least on...
by Diminished
Fri Sep 04, 2020 10:14 pm
Forum: 8-bit acorn hardware
Topic: Hello and my 'new' USA beeb kit
Replies: 14
Views: 554

Re: Hello and my 'new' USA beeb kit

I'm not an expert on Beeb hardware, but you're definitely in the right place.

Welcome.
by Diminished
Fri Sep 04, 2020 9:26 pm
Forum: 8-bit acorn software: classic games
Topic: BBC Elite source, now fully documented and explained
Replies: 75
Views: 3210

Re: BBC Elite source, now fully documented and explained

MarkMoxon wrote:
Fri Sep 04, 2020 11:00 am
  • Bitstick support
Huh. This I didn't know.

Has anyone ever looked at the NES port? ISTR Ian Bell saying that was his favourite 8-bit version, since they had to work out a way of drawing vectors using the console's tile-based graphics system.
by Diminished
Fri Sep 04, 2020 9:00 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

I wouldn't go risking more vintage hardware just for the sake of it... unless you really want to :) So I'm just thinking again about this glitching idea. The thing closest to the power supply is the presumed core of the byte processor -- its PC, stack, ROM, etc, so perhaps that will continue to run ...
by Diminished
Fri Sep 04, 2020 12:27 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Yeah, I can't trivially reproduce what you did, Chris. I can find values which put a 25 KHz square wave on LOAD HEAD and a 400 KHz square wave on INT, and I can find values which pull either or both of those pins high, but I'm not seeing the crazy superposition that you reported. I haven't tried oth...
by Diminished
Thu Sep 03, 2020 11:04 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Dug the Beeb out. With DFS 0.98, and no drive: Press BREAK, then ?&FE82=2 crashes the machine. However: Press BREAK, then ?&FE82=1:?&FE82=0:?&FE82=2 does not crash the machine. (?!) edit: Maybe it only works after the RESET pin is asserted? (Does BREAK do that?) edit2: Now ... I've dug the 'scope ou...
by Diminished
Thu Sep 03, 2020 9:09 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

I agree it's worth doing. I'm glad someone else volunteered. I can capture 8 parallel bits but that's all you'll get out of me. Has anyone tried inspecting what happens to the 8271 registers with either 2 or 4 written to the reset register? Does the chip even respond at that point? I don't have a Be...
by Diminished
Thu Sep 03, 2020 10:37 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Could a logic analyser be attached to an 8271 in-situ to try to understand the instruction set? Not "officially". As far as we know, you'd need to tap the thing's internal bus. If that could be done, the effort would be over very quickly. I've briefly thought about this possibility before, but mayb...
by Diminished
Thu Sep 03, 2020 7:36 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

I wish there were better photographs. Having two chips is very useful but the precipitate (if that's what it is) always seems to collect in the same places on whichever die is being looked at, so there are always parts of the chip that are obscured. I'd really like to give Degate a try, if I can con...
by Diminished
Thu Sep 03, 2020 6:57 am
Forum: 8-bit acorn software: classic games
Topic: Repton (1, the original) disc variants found
Replies: 7
Views: 668

Re: Repton (1, the original) disc variants found

Did you have any particular technique for working out where to break and what to save? I'd be interested in trying the same on the Repton 2 variant. Is there some common trick perhaps for the Superior games where the main game file(s) are not in the DFS catalog? I wonder if some stupid heuristic wo...
by Diminished
Wed Sep 02, 2020 7:26 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Well ... I took a shot at writing up the relationships between the inputs to the PLA and its outputs based on what we think we know about how the bus is split. The outputs are in die order. The results are weird, but there's one encouragement, which is that the ID1 + ID2 + ID3 tuple does seem to for...
by Diminished
Wed Sep 02, 2020 4:13 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

The next question is what determines the flow from segment to segment? Something encoded in the yield opcode? Or something hardcoded in the ROM? I had a go at addressing this (ho ho) earlier in this post . Basically the patent seems to state that "yield" and "declare next segment ID" are distinct i...
by Diminished
Wed Sep 02, 2020 1:32 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Sorry guesser -- went to bed, didn't see your post. Have a gawk at the patent if you get the chance, Rich, but yeah -- the input to the thing is supposed to be four bits of routine ID, four bits of segment ID, and two bits of something else (which are the rightmost two bits on the die, but we think ...
by Diminished
Wed Sep 02, 2020 1:04 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Here's guesser's readout with the bits reversed, and converted to hex. (edit: to clarify, that's the output table -- the one that the patent claims loads the PC). Four values differ from my attempt but I took no real care, so I don't doubt that his are more accurate. 27a 66 a7 a7 8e a7 2af 2ab 2c1 2...
by Diminished
Wed Sep 02, 2020 12:39 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

The results make no sense!

At least they do all seem to live within the 864 bytes of program, at least with the way I transposed them ... but they make no sense!
by Diminished
Wed Sep 02, 2020 12:22 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

My effort had bit 9 on the right and bit 0 (white) on the left, so the reverse of the "reg10" block, but I've really no idea any more. I got this load of nonsense (bits are reversed). 27a 66 a7 a7 8e a7 2af 2ab 2c1 27f 97 97 87 7e 32e 30e 30f 2ed 190 30c 30e 314 30e 30f 19d 1ad 205 307 30b 13 76 58 ...
by Diminished
Wed Sep 02, 2020 12:02 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Well I tried to read out the table of program counter values.

The results make absolutely no sense whatsoever.

I am officially declaring myself insane.
by Diminished
Tue Sep 01, 2020 6:36 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Yeah. I thought you originally read the tables the other way round, but maybe not. Ah sorry. Yeah I've only posted up the "address" side with the don't care states etc, and not read out the output bits yet. Ah right, I thought you'd done both halves. Sorry. So the don't care stuff makes more sense ...
by Diminished
Tue Sep 01, 2020 6:16 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

guesser wrote:
Tue Sep 01, 2020 6:14 pm
Wait, I think we're agreeing aren't we?
Yeah. I thought you originally read the tables the other way round, but maybe not.
by Diminished
Tue Sep 01, 2020 5:18 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

I'm no expert, as this thread verbosely documents, but the first thing is I've noticed is I think we might have been reading the address generator the wrong way round. I think the inputs arrive to the bigger table on the left, and the outputs leave via the smaller one on the right. At least, the top...
by Diminished
Tue Sep 01, 2020 3:04 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Looking at this now, in terms of working out how many distinct "routines" exist: Screenshot 2020-09-01 at 14.55.17.png Hypothesising: there's one routine in ROM per dispatcher request input ("interrupt line"). The above piece of circuitry's location might be betrayed by a unique feature it seems to ...
by Diminished
Tue Sep 01, 2020 2:42 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15300

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Perhaps this code is not supposed to be read as a continuous thing, but more as discrete blocks of code which can be executed in whichever order the dispatcher decides. It would be good to know if there's some sort of RET or YIELD opcode which marks the end of a segment. If anyone has any ideas or ...

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