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

discuss both original and modern hardware for the bbc micro/electron
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daveejhitchins
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Re: 8271 disc controller craziness -- do not try this at home!

Post by daveejhitchins » Tue Jul 07, 2020 5:15 am

Why not use both avenues? Just in case . . . And wouldn't a working part be better to de-cap? Or wouldn't it matter?

Dave H :D

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

Post by Pernod » Thu Aug 20, 2020 6:27 pm

Thanks to BeebMaster for donating the 8271's and Sean Riddle for decapping them, we now have preliminary pics at www.seanriddle.com/8271.
- Nigel

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

Post by scarybeasts » Thu Aug 20, 2020 7:42 pm

What a treat!
It's a beautiful picture but I have no real idea what I'm looking at. Anyone have any thoughts?


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

Post by BigEd » Thu Aug 20, 2020 7:56 pm

Certainly looks like a microcontroller - and the ROM looks readily decodable.

Here's a smaller version, for looking around - my computer can't deal with the full size:
https://www.dropbox.com/s/shkcidjtxl2t0 ... r.jpg?dl=0

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

Post by guesser » Thu Aug 20, 2020 8:00 pm

It does look somewhat micro-controller-ey, but my level of expertise is at the "enjoys reading Ken Shirriff's blog" level.

The bottom left corner looks rather ROM-like. There's a big array and a small one (microcode ROM and instruction decoding ROM?)
It does say "© intel 1978 μCODE" next to it but whether that means anything I've no idea. :lol:
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Re: 8271 disc controller craziness -- do not try this at home!

Post by BigEd » Thu Aug 20, 2020 8:18 pm

I might have over-played my confidence there, but perhaps wiser heads can chip in.

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

Post by Rich Talbot-Watkins » Thu Aug 20, 2020 8:21 pm

Great job! =D>

Don't really make much sense of it either, other than that there seems to be various ROM-like bits in the bottom left and the top right, and what looks a bit like RAM or registers bottom right and top left. There are also various other regular looking structures which also look a bit like ROMs of some sort.

What I can't find are the (at least) 35 8-bit "special registers" which we always assumed were equivalent to the microcontroller on-board RAM.

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

Post by dp11 » Thu Aug 20, 2020 10:26 pm

bottom left looks like 256 bytes of ROM.

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

Post by BigEd » Thu Aug 20, 2020 10:29 pm

That thing bottom right could be 22 bytes of register. Maybe, just maybe, 44.

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

Post by guesser » Thu Aug 20, 2020 10:29 pm

Counting things and guessing wildly (username checks out etc :lol:) the registery stuff in the bottom right looks 16 bits wide, and there's 10 rows the same with some more 16 bit wide things of a different design.

The big ROM-thing is vaguely binary-ish down the left side, but only has 54 rows and some combinations appear duplicated so not sure what's going on there. The columns are grouped into 8 groups of 4.

The smaller one to the side seems to be 82 x 10.

There's another 10 bit wide structure above the ROM-thing.

Top left looks like eight 8-bit wide registery-things.

I look forward to reading how wrong I was when someone who knows what they're doing looks at it :D
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Re: 8271 disc controller craziness -- do not try this at home!

Post by dp11 » Thu Aug 20, 2020 10:40 pm

I wonder if the 10 bit structure is either a timer or divider ?

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

Post by dp11 » Thu Aug 20, 2020 10:42 pm

have we actually got two different controllers ? one at the top and one at the bottom ?

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

Post by Rich Talbot-Watkins » Thu Aug 20, 2020 10:46 pm

There's another ROM-like structure kind of centre-right which has exactly 64 columns. No idea what that might be either.
image.png

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

Post by dp11 » Thu Aug 20, 2020 11:12 pm

My guess in right hand side power pad in GND with the data bus going down and around the corner

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

Post by Diminished » Fri Aug 21, 2020 12:26 am

Pretty.

If it's a microcontroller, or a microprocessor, do we have any guess as to what kind? I don't think there can have been too many candidates back then.

Perhaps one of these:

https://en.wikipedia.org/wiki/Intel_MCS-48

Or there were the proper CPU cores available at that time. Here are the 4-bit ones:

https://en.wikipedia.org/wiki/List_of_I ... processors

The 8271 data sheet itself mentions that the 8271 is compatible with the MCS-80 and MCS-85, so those chips were presumably around at the same time? Wikipedia thinks the MCS-80 was based on an 8080. The 8-bit ones are here:

https://en.wikipedia.org/wiki/List_of_I ... processors

I don't know if we can find die shots of any of these to compare.

Also, perhaps this might be worth keeping in mind:
Screenshot 2020-08-21 at 00.24.02.png

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

Post by guesser » Fri Aug 21, 2020 1:33 am

I was looking at die shots of the intel microcontrollers earlier. Couldn't find any similar, but of course there's only odd ones online.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by Diminished » Fri Aug 21, 2020 11:47 am

The bus in the top-left is interesting. I'm wondering if this is the "internal data bus" mentioned in the block diagram:

https://drive.google.com/file/d/19b-AsH ... sp=sharing

It continues across the width of the chip and no doubt connects up to various other things.

(Disclaimer: I have absolutely no idea what I am doing)
Last edited by Diminished on Fri Aug 21, 2020 12:14 pm, edited 2 times in total.

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

Post by dp11 » Fri Aug 21, 2020 11:57 am

Anyone go any good ways of us group working on identifying bits of this chip ?

The data sheet says it has a 16bit CRC generator. I haven't yet spotted a 16bit structure.

Thanks

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

Post by BeebMaster » Fri Aug 21, 2020 12:06 pm

This is very exciting, and all happened before I got the chance to say "it's been delivered today"!

Can anyone open the 120MB picture?
Image

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

Post by guesser » Fri Aug 21, 2020 12:08 pm

I think there's a limit to what can be done by looking for repeating structures in the metal layer. To work out what all the messy logic stuff is doing would need another image of the silicon with the appropriate illumination to discern the doped regions etc. (Plus someone competent at reversing gates from transistors!)

I seem to remember there being a way for newbies to contribute to reversing chips by tracing over the layers for a chunked up set of die shots, that's then processed into transistors and gates semi-automatically, guided by someone who knows what they're looking at. I think it was probably part of the visual6502 project?
Last edited by guesser on Fri Aug 21, 2020 12:11 pm, edited 2 times in total.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by guesser » Fri Aug 21, 2020 12:09 pm

BeebMaster wrote:
Fri Aug 21, 2020 12:06 pm
This is very exciting, and all happened before I got the chance to say "it's been delivered today"!

Can anyone open the 120MB picture?
I opened it in irfanview. Very slowly 😃
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Re: 8271 disc controller craziness -- do not try this at home!

Post by BeebMaster » Fri Aug 21, 2020 12:10 pm

There's a new picture in that link now as well, the previous one everyone has been looking at so far is an 8271-6 variety, I also sent an 8271 which has now been photographed.
Image

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

Post by BeebMaster » Fri Aug 21, 2020 12:16 pm

There's no hope on the Pi4, but my laptop loaded the big pictures in GThumb no problem in a few seconds.
Image

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

Post by Pernod » Fri Aug 21, 2020 12:25 pm

BeebMaster wrote:
Fri Aug 21, 2020 12:10 pm
There's a new picture in that link now as well, the previous one everyone has been looking at so far is an 8271-6 variety, I also sent an 8271 which has now been photographed.
Some notes from Sean:
One of the die shots is out there now and I’ll upload the other later today. The 2 dies look identical to me, but I haven’t compared them closely yet.

I’m not sure how I’ll remove the top metal layer; I normally put the die in a test tube with Whink and heat that in boiling water, but the die is stuck to the ceramic bottom and that’s too large to put in a test tube. I’ll figure something out.
----
I copied the pic of the 2nd die out to the same folder. I’ll do some more work this weekend.
Oh, and there's a 8272 at www.seanriddle.com/8272metal.jpg if anyone's interested.
- Nigel

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

Post by BigEd » Fri Aug 21, 2020 12:36 pm

There was a brief effort at crowdsourcing polygon capture within the visual6502 world, but it didn't come to anything.

Best results have come from individuals putting in the hours, using a tool like Inkscape or a photo editors.

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

Post by Diminished » Fri Aug 21, 2020 12:51 pm

Diminished wrote:
Fri Aug 21, 2020 11:47 am
The bus in the top-left is interesting. I'm wondering if this is the "internal data bus" mentioned in the block diagram:

https://drive.google.com/file/d/19b-AsH ... sp=sharing

It continues across the width of the chip and no doubt connects up to various other things.

(Disclaimer: I have absolutely no idea what I am doing)
Furthermore, these look like the connections from the bus to the big ROM looking thing in the bottom left. 8 bits seem to be tapped off the bus, and each bit makes four connections to the top of that structure, making it some sort of 8x4 thing:

https://drive.google.com/file/d/1YNsx49 ... sp=sharing

Hard to see the vertical lines from this photo. There's probably some logic there in between the bus taps and the ROM thing.
Last edited by Diminished on Fri Aug 21, 2020 12:53 pm, edited 1 time in total.

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

Post by guesser » Fri Aug 21, 2020 12:52 pm

It's hard to tell because the 8271 image is dirty and a couple of the "bits" are completely obscured, but the big ROM in the bottom left looks identical to me. There's one bit that looks different but I think it's an illusion caused by a spec of dirt.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by guesser » Fri Aug 21, 2020 12:53 pm

BigEd wrote:
Fri Aug 21, 2020 12:36 pm
There was a brief effort at crowdsourcing polygon capture within the visual6502 world, but it didn't come to anything.

Best results have come from individuals putting in the hours, using a tool like Inkscape or a photo editors.
I was just thinking in terms of several people not all starting vectorising the same part of the chip in an incompatible format :)
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Re: 8271 disc controller craziness -- do not try this at home!

Post by guesser » Fri Aug 21, 2020 12:54 pm

I must say I find this stuff fascinating and have been well and truly nerd-sniped :lol:
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Re: 8271 disc controller craziness -- do not try this at home!

Post by English Invader » Fri Aug 21, 2020 1:01 pm

I tried to open the first picture in the list and it froze up my system :lol:.

May I ask why this is of interest to the MAME community?

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