Search found 523 matches

by Diminished
Fri Aug 28, 2020 2:12 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Try this: https://siliconpr0n.org/wiki/doku.php?id=rom:mask I don't know if this is exactly how this works, since this is an NMOS process and I think the schematic examples there are CMOS ones. I didn't show any ROM in my picture but the one earlier in this page that guesser posted shows the individ...
by Diminished
Fri Aug 28, 2020 12:42 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

The ROM is constructed like this That's a very instructive picture, thanks. Looking at the bits you've transcribed, it starts 01101001 01101011 ... what's the gather method to go from that array of transcribed bits to the data bytes? (Below is the first 8-byte line.) 03 F9 FD 08 FF 00 46 FB Cheers ...
by Diminished
Thu Aug 27, 2020 9:26 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

So I put together some toolery to automate these transpositions. I was getting confused over what combinations I'd tried and hadn't tried, so I just wrote something to produce all possible combinations and dump them all to files. It might be useful for something else at some point. Here are my 32 tr...
by Diminished
Thu Aug 27, 2020 7:46 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

I've tried every transposition I can think of in all sorts of combinations -- inversions, bit reversals, byte reversals, reversing 8-byte chunks (as would happen if the 0:2 and 3:7 bits were inverted relative to one another) and nothing comes out that 8039dasm can make any sense of.
by Diminished
Thu Aug 27, 2020 7:42 pm
Forum: 8-bit acorn software: other
Topic: Discbeast, new disc and archival utility -- NEED VOLUNTEERS
Replies: 94
Views: 4613

Re: Discbeast, new disc and archival utility -- NEED VOLUNTEERS

Interesting. I guess the IMD format isn't a sophisticated enough medium-level representation.

Ah well.
by Diminished
Thu Aug 27, 2020 3:16 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

guesser wrote:
Thu Aug 27, 2020 2:52 pm
Indeed, but the bus running through the middle does seem to be 10-bit. It was suggested this might be the 8 data bits and two external address inputs.
I suggested the bus was 8-bit, and that it was the internal bus, i.e. the one that is clearly mentioned on the data sheet.
by Diminished
Thu Aug 27, 2020 1:23 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

What if the address decoder ROM bits are inverted, too?

You could have weird arrangements where bits 0-2 count upwards, but bits 3-7 count downwards ...
by Diminished
Thu Aug 27, 2020 10:20 am
Forum: 8-bit acorn software: other
Topic: Discbeast, new disc and archival utility -- NEED VOLUNTEERS
Replies: 94
Views: 4613

Re: Discbeast, new disc and archival utility -- NEED VOLUNTEERS

disk-analyse has a good moan over trying to convert the 40 track version posted earlier to IMD: $ ./disk-analyse 3DPool.hfe 3DPool.imd *** T0.0: Unexpected track length (seen 51187, expected 50075) *** T1.0: Unexpected track length (seen 51187, expected 50075) *** T2.0: Unexpected track length (seen...
by Diminished
Wed Aug 26, 2020 11:09 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

This is a slightly philosophical question: should the layers in the chip be kept separate in the vectorization, or should everything that's the same net be part of the same path? For instance the ground net, should it all be one, or have the metal layer on one path and silicon on another. It's easy...
by Diminished
Wed Aug 26, 2020 7:39 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

I'm happy to do some. Can we switch to svg though? I loading the xcf files makes my pc chug for a couple of minutes! I'll convert all those new paths over to my file next. I could put it in git too as it should be possible to merge changes to the svg in theory ... I guess ... do you want to fix tha...
by Diminished
Wed Aug 26, 2020 6:27 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

That thick rail with 4 big contact cuts is connected by a very wide crossunder on the right to the red rail. It also wiggles left and down to connect to some single gate, between the yellow and orange bus wires. I think you mean this one? That will have been left out because I was only concerning m...
by Diminished
Wed Aug 26, 2020 6:10 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

The thick rail that's 3 rails north, with 13 medium contacts is connected directly to the blue rail on the right by a vertical connection, and also goes off to the left and then south, to become a rail above one of the regular structures. Ah, that's irritating. Thanks. I'll tackle that now. Keep em...
by Diminished
Wed Aug 26, 2020 6:03 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Are you on the stardot Discord diminished? I'm afraid not. (Discord stores and sells every single thing you say. I don't have a Facebook or Twitter account either. I'm not a fan of the modern corporate Internet.) Here are my latest GIMP files. As before, there aren't any actual 8271 snaps included....
by Diminished
Wed Aug 26, 2020 3:53 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

I had a go at vectorising the entirety of the metal layer VCC and GND connections. This was not fun but it should make things a lot easier. Here are the results at 25%. https://drive.google.com/file/d/1773TmX8tLrCYp2dYvrE8vZtSbP1nG5oU/view?usp=sharing I'll add the pad naming and get a new set of pro...
by Diminished
Wed Aug 26, 2020 1:19 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Has anyone spotted any differences between the 8271 and the 8271-6? Only difference according to the datasheet is the operating temperature range, so maybe it only comes about at the testing/certification stage after manufacture. I think there was a -8 once upon a time as well, haven't seen one of ...
by Diminished
Tue Aug 25, 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: 15716

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

I think there is at least one clue that the bit ordering is right, which is the 2/8 split in the structure that feeds the ROM's address lines. I could be wrong but I feel like that does reflect the A[1:0]/D[7:0] nature of the internal register block mentioned in the data sheet. I was hoping we could...
by Diminished
Tue Aug 25, 2020 8:45 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

A quick PHP hack on the bytes collected shows how many times each of them occurs. These are listed the "wrong way round", with the frequency first and the byte second (so I could sort them in order of commonness). I left in the ones that never occur at the bottom (the zeroes). Most possible bytes do...
by Diminished
Sun Aug 23, 2020 1:18 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

I don't understand the circuit either ... I don't get how those top six rows somehow act as switches (although they're fed with assumed complementary pairs of inputs, whereas the other rows presumably aren't), but the logic might work like this:
romsplaining_1.jpg
by Diminished
Sun Aug 23, 2020 12:23 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Yeah, it's a little disappointing how much muck there is on the new pictures ... but they're certainly enough for some more poking around.

I suppose you can chalk up yet another reason why the 8271 was a poor choice for the Proton's FDC ...
by Diminished
Sun Aug 23, 2020 10:59 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Where is the decoding logic for demultiplexing 3 bits into 8 lines, though? It was under the metal layer, predictably enough. Perhaps this is how the column decoding works? The address decoder rom energises one of the rows (not shown here), and then these three bits select one of eight columns? Fli...
by Diminished
Sun Aug 23, 2020 12:11 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Well, this is kind of interesting, although it produces more questions than answers. my_brain_hurts_1.jpg I had a bash at tracing the rightmost connections in each of the clusters of 3 at the very bottom of the 10-way structure, immediately to the right of where they connect to the bus (with the exc...
by Diminished
Sat Aug 22, 2020 9:46 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

OK Here's the 531 megapixel GIMP file at 70 MB: https://drive.google.com/file/d/1R9aTZRjWVFfIKmZcgOMjtvbsFLxHV1xH/view?usp=sharing And a 133 megapixel one at 19 MB: https://drive.google.com/file/d/1cyrigX1JU95iW_KpQvPOH5joFZbKYaHk/view?usp=sharing Neither of these contains the actual die photo. I us...
by Diminished
Sat Aug 22, 2020 5:27 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

With the arrival of the cleaner metal photos, I took the new 8271-6metal2 and used it as the basis for another attempt, this time properly vectorising everything I've looked at so far. Here is an improved trace at 25%: https://drive.google.com/file/d/10CsnFIUivEzKr3whLoxMsTk0sx25kX17/view?usp=sharin...
by Diminished
Sat Aug 22, 2020 10:14 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Something interesting with these suspected 10 bit registers: 10bitregs_horiz_1.jpg I started trying to follow the traces within this structure. The vertical red and blue ones are VCC and GND. Then I added in the horizontal ones in yellow, and I noticed something about the bottom one (nearest the con...
by Diminished
Fri Aug 21, 2020 9:40 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

The data sheet says it has a 16bit CRC generator. I haven't yet spotted a 16bit structure. Looking at where my bus traces finished up, and the fact that they terminate in the same bit order as the other 8-bit connections to the bus, I assume these make another vertical leap downwards. There's a sec...
by Diminished
Fri Aug 21, 2020 8:18 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

A0 A1 do come from the outside world , but I don't understand why they would go into a structure like the databus does . Well, I'm thinking this would be normal digital logic practice? A0 and A1 would have to be clocked into a register somewhere ("sampled and held") to make sure the 8271 didn't exp...
by Diminished
Fri Aug 21, 2020 7:57 pm
Forum: programming
Topic: A new BBC Micro MOS Reassembly
Replies: 32
Views: 1680

Re: A new BBC Micro MOS Reassembly

Awesome.
by Diminished
Fri Aug 21, 2020 7:45 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

So I have my suspicions about this structure. 8bit10bit.jpg It seems to be 10 bits wide, but only 8 bits are attached to the bus. datasheet_A_D.jpg Could these be the one or more of the command / parameter / status / result registers, with two bits A0 and A1 coming in from the outside world? I dunno.
by Diminished
Fri Aug 21, 2020 7:06 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 445
Views: 15716

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

Did a bit more gawping and noticed the bus turning south, right in the middle of the die. These lines are really hard to follow but I tried as best I could to trace them. I lost half of them, but the other half seemed tentatively to end up at the points denoted by the question marks. With respect to...

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