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

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

Post by scarybeasts » Tue Jun 23, 2020 10:20 pm

Hi,

I encountered an 8271 behavior (and a bit of data loss) that was sufficiently wild to investigate in more detail.

I wrote a blog post with a video and some pictures: https://scarybeastsecurity.blogspot.com ... -chip.html

But if you want to jump straight to the weirdness -- and this is the "do NOT try this at home thing", no responsibility accepted for damages, etc.

With an Intel 8271 as your disc chip:
?&FE82=4

It makes my drive go crazy: https://www.youtube.com/watch?v=sRcb3goLbZI

It doesn't seem to damage my drives but it may damage yours so caveat empor! And depending on the drive, it _will_ erase data on the disc _despite any hardware write protect tab_.



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Chris

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

Post by kieranhj » Wed Jun 24, 2020 8:17 am

Great blog post Chris, a really interesting read. Thank you.

I guess even Kevin Edwards’ tape copy protection system decided that would have been step of evil too far!!
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Re: 8271 disc controller craziness -- do not try this at home!

Post by Kazzie » Wed Jun 24, 2020 8:50 am

Weird, and thoroughly interesting.

Did you try to poke any of the other bits in the reset register?
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Re: 8271 disc controller craziness -- do not try this at home!

Post by BigEd » Wed Jun 24, 2020 10:06 am

I like the idea that the 8271 is a microcontroller in disguise, and that the ROM could be extracted.

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

Post by scarybeasts » Wed Jun 24, 2020 10:29 am

Kazzie wrote:
Wed Jun 24, 2020 8:50 am
Weird, and thoroughly interesting.

Did you try to poke any of the other bits in the reset register?
Yes! ?&FE82=2 also does something. It also causes crazy signals to go out on some of the pins, just different ones! It seems to affect host side rather than drive side. If you try it (caveat empor etc.!), your machine will wedge. Memory is hazy here but I think it's because the NMI pin is toggled at a very high frequency. Not much going to get done by the 6502 / OS under those circumstances.


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

Post by scarybeasts » Wed Jun 24, 2020 10:37 am

BigEd wrote:
Wed Jun 24, 2020 10:06 am
I like the idea that the 8271 is a microcontroller in disguise, and that the ROM could be extracted.
It's looking more likely. The internet is doing its thing and some kind commentator found this:
https://dewiki.de/Lexikon/Intel_MCS-48

Translated to English, it makes the clear claim: "8271" "Programmable floppy disk control module (permanently programmed interface module based on 8041)". No reference cited though.


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

Post by Pernod » Wed Jun 24, 2020 12:45 pm

Thanks, and shared amongst the MAME community. Seems there's interest in seeing the 8271 decapped to extract the ROM.
- Nigel

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

Post by Coeus » Thu Jun 25, 2020 9:13 pm

Very interesting, especially the bit about the 8041. Looking at what commands it provides things like counting the number of step pulses itself and auto-generating track and sector ID headers rather than getting the host microprocessor to do it would be easier with a chip based on a micro-controller than one assembled from counters and random logic. Then missing out the data separator is a curious choice - yes it can be done with a couple of TTL chips but integrating it would have reduced component count. It's interesting to compare the 8271 and the WD1770.

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

Post by scarybeasts » Fri Jun 26, 2020 8:39 am

Coeus wrote:
Thu Jun 25, 2020 9:13 pm
It's interesting to compare the 8271 and the WD1770.
I can't decide which I dislike the most :lol:


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

Post by scarybeasts » Fri Jun 26, 2020 8:42 am

Pernod wrote:
Wed Jun 24, 2020 12:45 pm
Thanks, and shared amongst the MAME community. Seems there's interest in seeing the 8271 decapped to extract the ROM.
Is there anything we / I could do to increase the chances of this happening? I have a feeling that if we had a clock-by-clock understanding of what the 8271 does, we might see opportunities to program it in weird and wonderful ways.

Also, perhaps it can be done without decapping? The crazy modes I found might be debug / test modes that would enable examining it externally with a suitable breadboard setup?


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

Post by BigEd » Fri Jun 26, 2020 8:45 am

There's certainly a chance: the fonts of the small cheap 4-pen plotter were read from the 6502-based microcontroller. And we're told there's a test mode in this case which involves pulling a pin to 12V.

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

Post by Kevin Edwards » Fri Jun 26, 2020 9:02 pm

Great article, Chris.

I do have a soft spot for the 8271. I wrote a couple of articles in The Micro User about it too.

I wish i'd been able to release my disk protection system too..unfortunately no one could duplicate it!

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

Post by scarybeasts » Fri Jun 26, 2020 9:11 pm

Kevin Edwards wrote:
Fri Jun 26, 2020 9:02 pm
I wish i'd been able to release my disk protection system too..unfortunately no one could duplicate it!
Sounds interesting.
Is it described anywhere, or do you remember it well enough to describe it?


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

Post by Kevin Edwards » Fri Jun 26, 2020 9:50 pm

Not described or documented I'm afraid.

I wish i had kept the notes and disks too...not discovered them yet during my archiving sessions.

It used various different techniques to defeat all of the disk copiers around at that time - Copy-All, Vector2, Disk Duplicator etc.

I can't remember all of the details exactly after all this time.

Lots of very unusual track formats which i expected to either give errors or not.

Unformatted tracks that needed a blank disk to copy

Formatted tracks with some extra large sectors, which i then wrote smaller sized sectors over. But hid data in the end part of the large sectors.

Lots of confusing CHRN values that confused the copiers - with some of them actually having readable data, but with non-matching sector sizes.

One other plan I had was to write 'special' tracks using a 1770 ( in single density mode) which allowed you to do things that the 8271 couldn't.

And other stuff I just can't remember.

On top of that the usual 6522 decoders that you are familiar with.

All the commercial disk duplicating machines failed miserably trying to copy even the simple stuff. Each disk had to be created, one by one, using a BBC Micro which wasn't a good solution for most big software publishers.

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

Post by BeebMaster » Sat Jun 27, 2020 1:02 am

I have ceramic 8271 stock, I'm sure one could be sacrificed in the cause of understanding it better. In fact one of the last batch was duff, maybe that one.

Quite a few of them were the 8271-6 variant which I don't think I'd ever seen before. The only functional difference is a slighly lower maximum operating temperature

I've been looking in the Intel databook for the years of production. In 1978 and 1979, the 8271 datasheet in those years is stamped "preliminary". Also it appears from later years that there was an 8271-8 variant for a while, haven't looked into what differences that had.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by BigEd » Sat Jun 27, 2020 7:03 am

Oh, ceramic is a massive win: you can split the package with a cold chisel, and it might even not stop the thing from working.

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

Post by Kazzie » Sat Jun 27, 2020 10:38 am

I'd been thinking about that, as I have a ceramic 8271 I bought from Beebmaster for my System project, but was reluctant to pop the lid off it and end up searching for a replacement. But if Beebmaster's got one sat on the faulty pile, that sounds like an ideal candidate to send off to a friendly decapper. I'm not quite up to the task yet, as my single experiment with a busted EPROM sadly proved:
IMG_20200627_1024492.jpg
DSC_0420.JPG
I don't quite have the macro "reach" with my current camera setup either. :(
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Re: 8271 disc controller craziness -- do not try this at home!

Post by scarybeasts » Sun Jun 28, 2020 12:33 am

Kazzie wrote:
Sat Jun 27, 2020 10:38 am
I'd been thinking about that, as I have a ceramic 8271 I bought from Beebmaster for my System project, but was reluctant to pop the lid off it and end up searching for a replacement. But if Beebmaster's got one sat on the faulty pile, that sounds like an ideal candidate to send off to a friendly decapper.
Is there any one on these forums we know with decapping experience? I bet some initial hi-res die shots would resolve a lot of uncertainty regarding what sort of beast we are dealing with.


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

Post by BeebMaster » Sun Jun 28, 2020 5:33 pm

Right, I'm ready. What do I do next?
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Re: 8271 disc controller craziness -- do not try this at home!

Post by Kazzie » Sun Jun 28, 2020 7:58 pm

scarybeasts wrote:
Sun Jun 28, 2020 12:33 am
Kazzie wrote:
Sat Jun 27, 2020 10:38 am
I'd been thinking about that, as I have a ceramic 8271 I bought from Beebmaster for my System project, but was reluctant to pop the lid off it and end up searching for a replacement. But if Beebmaster's got one sat on the faulty pile, that sounds like an ideal candidate to send off to a friendly decapper.
Is there any one on these forums we know with decapping experience? I bet some initial hi-res die shots would resolve a lot of uncertainty regarding what sort of beast we are dealing with.


Cheers
Chris
If there's nobody over here, perhaps Pernod knows someone on the MAME side with decapping experience? (Quoting to provoke the board into notifying him...)
Pernod wrote:
Wed Jun 24, 2020 12:45 pm
Thanks, and shared amongst the MAME community. Seems there's interest in seeing the 8271 decapped to extract the ROM.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by BigEd » Sun Jun 28, 2020 8:02 pm

Here's a catalogue of ways to tackle it:
https://siliconpr0n.org/wiki/doku.php?i ... glass_frit
and here's a video of one method (heating the top for 20 seconds while heat-sinking the bottom):
https://www.youtube.com/watch?v=wnQ8Td1y_dM

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

Post by Pernod » Sun Jun 28, 2020 8:11 pm

Kazzie wrote:
Sun Jun 28, 2020 7:58 pm
If there's nobody over here, perhaps Pernod knows someone on the MAME side with decapping experience? (Quoting to provoke the board into notifying him...)
The board isn't that intelligent, it doesn't notify me, though I do check frequently.

I haven't put the word out yet that we'd like a 8271 decapped, but will. I wouldn't expect any results anytime soon though. My understanding is that they go to CAPS0ff, but have no idea how requests are prioritised.
- Nigel

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

Post by Kazzie » Sun Jun 28, 2020 8:26 pm

Pernod wrote:
Sun Jun 28, 2020 8:11 pm
Kazzie wrote:
Sun Jun 28, 2020 7:58 pm
If there's nobody over here, perhaps Pernod knows someone on the MAME side with decapping experience? (Quoting to provoke the board into notifying him...)
The board isn't that intelligent, it doesn't notify me, though I do check frequently.

I haven't put the word out yet that we'd like a 8271 decapped, but will. I wouldn't expect any results anytime soon though. My understanding is that they go to CAPS0ff, but have no idea how requests are prioritised.
Ah, my profile settings have me notified (at the top of the forum page) when I'm quoted in a post, which I think is the default that applied when I signed up. Never mind.

Still, thanks for putting the feelers out on the MAME side of things. :)
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Re: 8271 disc controller craziness -- do not try this at home!

Post by Pernod » Sun Jul 05, 2020 3:40 pm

I have an offer to decap and photo a 8271, from Sean Riddle in OK, USA. How do we want to coordinate this effort? I can pass on his contact details to whoever wants to lead this.
- Nigel

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

Post by Diminished » Mon Jul 06, 2020 1:18 pm

Been wanting someone to behead an 8271 for a while now

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

Post by BeebMaster » Mon Jul 06, 2020 1:32 pm

Am I donating the 8271? What happens next?
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Re: 8271 disc controller craziness -- do not try this at home!

Post by Kazzie » Mon Jul 06, 2020 8:46 pm

Beebmaster, if you want to contact Sean yourself (via Pernod) you could probably organise shipping the chip to him. Or if you'd like me to play middle-man, I'd be happy to do so.
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Re: 8271 disc controller craziness -- do not try this at home!

Post by dp11 » Mon Jul 06, 2020 9:32 pm

I'm happy to decap and photo the die here in the UK.

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

Post by IanB » Mon Jul 06, 2020 9:50 pm

I have several dead 8271s including a ceramic one which I think would be much easier to decap as you can split the top off it.

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

Post by Pernod » Mon Jul 06, 2020 10:10 pm

dp11 wrote:
Mon Jul 06, 2020 9:32 pm
I'm happy to decap and photo the die here in the UK.
I'd already PM'd Sean's shipping details to Beebmaster, but haven't yet responded to Sean's offer, and have no idea when he would actually get it done.

If the 8271 donors would prefer to keep it in the UK, and probably get it done quicker, then let me know so I can thank Sean for his offer but decline due to having a more local solution.
- Nigel

BBC Model B: ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, BeebZIF, etc.

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