6 ms·

Reverse engineering a forgotten 1970s Intel dual core beast: 8271, a new ISA

169 points by scarybeast 6y ago

ajross 6y ago
I love these die shot RE walkthroughs. This is such a weird choice though; almost no one used this chip for production hardware. The WD 17xx series was the king of floppy controllers in the 70's and early 80's (well, if you ignore Woz's masterpiece, which was discrete logic). Seems like if you're going to reverse an obscure chip, something with a more exotic application would have been more fun?
- scarybeast 6y ago
  We definitely wanted fun! I guess there are two ways to slice and dice it: 1) fun because the application is exotic / iconic, or 2) fun because the chip is exotic. This is definitely a case of the latter: an exotic chip with interesting history.
  - bane 6y ago
    The next goal should be trying to write a demo for it and enter it into Demosplash 2021.
- rbanffy 6y ago
  > Woz's masterpiece, which was discrete logic It had the downside of requiring precise timing. This is an issue if you wanted a faster (or even a slightly improved) 6502 in the machine. Oh well...
  - pvg 6y ago
    This made me realize that Zip chips were a lot more complicated than kid-me thought: https://en.wikipedia.org/wiki/Apple_II_accelerators#Zip_Chip_%E2%80%93_Zip_Technologies https://en.wikipedia.org/wiki/Apple_II_accelerators#Zip_Chip...
    - rbanffy 6y ago
      Those things were amazing engineering. Someone's probably making something like it for the retrocomputing crowd. With current tech it should be trivial to keep all of the RAM in the module and just asynchronously push some writes out (video and IO) at Apple II speeds.
  - nradov 6y ago
    Back then no one really expected microcomputer hardware architectures to have a long lifespan or allow for incremental CPU upgrades every year.
  - ajross 6y ago
    None of the Apple II's competitors exploited that, though. EVERYTHING in that world of software was built around tight hardware assumptions. Atari, VIC, Commodore, none of them ever shipped a faster CPU. That needed to wait for later architectures. No, the Disk II was absolutely a masterpiece. Go back to the linked article, think about everything this very complicated chip did, and recognize that Woz made a card that did exactly the same thing out of 6 chips you could buy at Radio Shack and two tiny ROMs.
    - rbanffy 6y ago
      I am familiar with the design. At the time, the only computers that were less timing dependent were the S-100 and CP/M boxes where you could swap out a CPU for a faster one if memory speed permitted. I don't consider it a mistake - nobody at the time was realizing that we all would, eventually, move our software to faster computers every couple years. Woz is brilliant, but he couldn't have foreseen it and, as you point out, almost nobody did.
jlarcombe 6y ago
Incredible stuff!
rbanffy 6y ago
My guess is that, at some point, a manager at Acorn asked which disk controller would the engineers recommend and they, obviously joking, said "8271". When they realized what they had done, it was too late.
- fredoralive 6y ago
  If this in the context of the BBC Micro, Acorn had already used the 8271 for floppy support with previous “System” and “Atom” models[1], so it’s probably chosen through inertia from a previous design choice. As for the older systems, does anyone have a date for the WD 1771 (the more common alternative)? The data sheet shown on the Wikipedia page is dated April 1979, and if that’s the release date then it would have been a new, unproven part compared to the intel chip when the System and Atoms were released 1979/80, assuming the floppy drive was an early upgrade (again, I don’t have dates to hand). [1] http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Acorn_fdc.html http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Aco...
  - kens 6y ago
    Google Books shows the WD1771 available and in use in 1977 with more products using it in 1978. (I find Google Books very useful for this sort of archaeology. Change the time range to "1977-1980", search for "wd1771", and then sort by date. Of course this isn't thorough, but it gives a good overview for little effort.)
    - fredoralive 6y ago
      Thank you for the research. In that case I guess it’s more of a wrong bet on part choice in 1979 I guess.
      - rbanffy 6y ago
        So, it could still be a joke ;-)
    - codetrotter 6y ago
__d 6y ago
The decision to use this chip (vs the WD) in the BBC Micro made me wonder if there were other obvious-in-hindsight bad/weird/hackish choices in classic computer design? The PC-AT's use of the keyboard controller to control A20 and CPU reset comes to mind. Any others?
- Jeema101 6y ago
  Several video game consoles from back in the day (the Magnavox Odyssey 2 and Entex Adventurevision) used the MCS-48 microcontroller mentioned in this write up instead of more conventional CPUs of the time like the 6502 or Z80, which seems a bit strange. Having dabbled in both MCS-48 and 6502 assembly I can tell you it was probably not done to make software development easier. :) I suspect maybe the hardware was just easier to design around a microcontroller? ...but there could have been other reasons...
  - Marazan 6y ago
    Both the 6502 and Z80 were designed/imagined for use in embedded systems, not the general purpose computers they became famous in.
dboreham 6y ago
The D765 was a D765B, probably a shrunk version, hence the different die size.
lathiat 6y ago
The floppy drive controller chip costing and being better than the main CPU reminds me of some of my arduino projects. For example I was driving a GSM Modem (over serial) which contained a comparatively advanced ARM SoC driving it.. from an AT Mega 8-bit micro that I was programming. It was great educationally, but kindof hilarious :)
- jandrese 6y ago
  The Commodore 64's disk drive was more powerful than the CPU, containing the same 6502 as well as a pair of 6522s. Amusingly some programs would upload mathematical calculations to the disk drives to speed up processing. https://www.lemon64.com/forum/viewtopic.php?t=27911 https://www.lemon64.com/forum/viewtopic.php?t=27911
  - ChickeNES 6y ago
    Same thing with early laser printers. The original Apple Laserwriter had a faster clocked 68000 compared to the original 128k/512k Mac
    - tonyedgecombe 6y ago
      But then it did have to run PostScript which was very slow on those early devices.
intricatedetail 6y ago
Is there a tech available currently to decap and photo chips at home? For example reverse engineering old PAL chips?
- krallja 6y ago
  Scanning just uses a microscope and open source panorama stitching software: http://www.righto.com/2015/12/creating-high-resolution-integrated.html http://www.righto.com/2015/12/creating-high-resolution-integ... Home decapping is possible, from what I can tell, but uses methods like “fuming nitric acid” and “blowtorch”, neither of which I would really want to experiment with right now. resilicon.reddit.com is becoming fairly active, if you have an interest.
- kens 6y ago
  These chip come in a ceramic package, so decapping is a simple matter of tapping along the seam with a chisel. If you want high-quality die photos, you'll need a metallurgical microscope, which shines the light down through the lens. I got my microscope on eBay. Once you have a bunch of die photos, you can stitch them together with a program such as Hugin.
userbinator 6y ago
A lot of special-purpose ICs are actually general-purpose processors with a mask ROM (or sometimes EEPROM, with interesting consequences), since writing the "firmware" for different functionality is easier than doing a whole "hard-coded" chip design --- the various USB-to-X adapters are one common example of this.
- 737maxtw 6y ago
  A large number of Realtek products are some form of MIPS core (or at least used to be).
- segfaultbuserr 6y ago
  A few days ago, I brought an USB-to-serial chip made by an obscure manufacturer. I found the RX/TX ports were working but control signals were not, I poked around the chip with an oscilloscope and found those pins were high-impedance, the chip didn't even attempt to output anything. I contacted tech support. They told me to buy a new one because my chip was an old batch without this feature (I guess it's a bug), but they can also provide a firmware update to me under NDA. It's microcontroller all the way down. Fun fact: It's also how those fake FTDI FT232 chips on the gray market were made. Counterfeiters just picked a cheap general-purpose microcontroller in mass production and wrote a Mask ROM for it. What's funny is that, the counterfeit chips actually have better process node than the real one (it doesn't mean it's better, though). https://zeptobars.com/en/read/FTDI-FT232RL-real-vs-fake-supereal https://zeptobars.com/en/read/FTDI-FT232RL-real-vs-fake-supe...
  - marcan_42 6y ago
    They are better though: the clones fixed bugs that the original FTDIs had (bugs bad enough to make certain modes completely useless). https://twitter.com/marcan42/status/695292366639378433?s=19 https://twitter.com/marcan42/status/695292366639378433?s=19 Don't buy FTDI chips; their malicious driver incident that bricked clones (by exploiting another bug in the EEPROM write support in their own chips!) should be enough to convince every board designer to stay away from them.
mrlonglong 6y ago
Got one of these in my Beeb, never knew it was a dual core monster. No bloody wonder they were so expensive back in the day.

169 points by scarybeast 6y ago

I love these die shot RE walkthroughs. This is such a weird choice though; almost no one used this chip for production hardware. The WD 17xx series was the king of floppy controllers in the 70's and early 80's (well, if you ignore Woz's masterpiece, which was discrete logic). Seems like if you're going to reverse an obscure chip, something with a more exotic application would have been more fun?

scarybeast 6y ago
We definitely wanted fun! I guess there are two ways to slice and dice it: 1) fun because the application is exotic / iconic, or 2) fun because the chip is exotic. This is definitely a case of the latter: an exotic chip with interesting history.
- bane 6y ago
  The next goal should be trying to write a demo for it and enter it into Demosplash 2021.
rbanffy 6y ago
> Woz's masterpiece, which was discrete logic It had the downside of requiring precise timing. This is an issue if you wanted a faster (or even a slightly improved) 6502 in the machine. Oh well...
- pvg 6y ago
  This made me realize that Zip chips were a lot more complicated than kid-me thought: https://en.wikipedia.org/wiki/Apple_II_accelerators#Zip_Chip_%E2%80%93_Zip_Technologies https://en.wikipedia.org/wiki/Apple_II_accelerators#Zip_Chip...
  - rbanffy 6y ago
    Those things were amazing engineering. Someone's probably making something like it for the retrocomputing crowd. With current tech it should be trivial to keep all of the RAM in the module and just asynchronously push some writes out (video and IO) at Apple II speeds.
- nradov 6y ago
  Back then no one really expected microcomputer hardware architectures to have a long lifespan or allow for incremental CPU upgrades every year.
- ajross 6y ago
  None of the Apple II's competitors exploited that, though. EVERYTHING in that world of software was built around tight hardware assumptions. Atari, VIC, Commodore, none of them ever shipped a faster CPU. That needed to wait for later architectures. No, the Disk II was absolutely a masterpiece. Go back to the linked article, think about everything this very complicated chip did, and recognize that Woz made a card that did exactly the same thing out of 6 chips you could buy at Radio Shack and two tiny ROMs.
  - rbanffy 6y ago
    I am familiar with the design. At the time, the only computers that were less timing dependent were the S-100 and CP/M boxes where you could swap out a CPU for a faster one if memory speed permitted. I don't consider it a mistake - nobody at the time was realizing that we all would, eventually, move our software to faster computers every couple years. Woz is brilliant, but he couldn't have foreseen it and, as you point out, almost nobody did.

jlarcombe 6y ago

Incredible stuff!

rbanffy 6y ago

My guess is that, at some point, a manager at Acorn asked which disk controller would the engineers recommend and they, obviously joking, said "8271". When they realized what they had done, it was too late.

fredoralive 6y ago
If this in the context of the BBC Micro, Acorn had already used the 8271 for floppy support with previous “System” and “Atom” models[1], so it’s probably chosen through inertia from a previous design choice. As for the older systems, does anyone have a date for the WD 1771 (the more common alternative)? The data sheet shown on the Wikipedia page is dated April 1979, and if that’s the release date then it would have been a new, unproven part compared to the intel chip when the System and Atoms were released 1979/80, assuming the floppy drive was an early upgrade (again, I don’t have dates to hand). [1] http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Acorn_fdc.html http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Aco...
- kens 6y ago
  Google Books shows the WD1771 available and in use in 1977 with more products using it in 1978. (I find Google Books very useful for this sort of archaeology. Change the time range to "1977-1980", search for "wd1771", and then sort by date. Of course this isn't thorough, but it gives a good overview for little effort.)
  - fredoralive 6y ago
    Thank you for the research. In that case I guess it’s more of a wrong bet on part choice in 1979 I guess.
    - rbanffy 6y ago
      So, it could still be a joke ;-)
  - codetrotter 6y ago

__d 6y ago

The decision to use this chip (vs the WD) in the BBC Micro made me wonder if there were other obvious-in-hindsight bad/weird/hackish choices in classic computer design? The PC-AT's use of the keyboard controller to control A20 and CPU reset comes to mind. Any others?

Jeema101 6y ago
Several video game consoles from back in the day (the Magnavox Odyssey 2 and Entex Adventurevision) used the MCS-48 microcontroller mentioned in this write up instead of more conventional CPUs of the time like the 6502 or Z80, which seems a bit strange. Having dabbled in both MCS-48 and 6502 assembly I can tell you it was probably not done to make software development easier. :) I suspect maybe the hardware was just easier to design around a microcontroller? ...but there could have been other reasons...
- Marazan 6y ago
  Both the 6502 and Z80 were designed/imagined for use in embedded systems, not the general purpose computers they became famous in.

dboreham 6y ago

The D765 was a D765B, probably a shrunk version, hence the different die size.

lathiat 6y ago

The floppy drive controller chip costing and being better than the main CPU reminds me of some of my arduino projects. For example I was driving a GSM Modem (over serial) which contained a comparatively advanced ARM SoC driving it.. from an AT Mega 8-bit micro that I was programming. It was great educationally, but kindof hilarious :)

jandrese 6y ago
The Commodore 64's disk drive was more powerful than the CPU, containing the same 6502 as well as a pair of 6522s. Amusingly some programs would upload mathematical calculations to the disk drives to speed up processing. https://www.lemon64.com/forum/viewtopic.php?t=27911 https://www.lemon64.com/forum/viewtopic.php?t=27911
- ChickeNES 6y ago
  Same thing with early laser printers. The original Apple Laserwriter had a faster clocked 68000 compared to the original 128k/512k Mac
  - tonyedgecombe 6y ago
    But then it did have to run PostScript which was very slow on those early devices.

intricatedetail 6y ago

Is there a tech available currently to decap and photo chips at home? For example reverse engineering old PAL chips?

krallja 6y ago
Scanning just uses a microscope and open source panorama stitching software: http://www.righto.com/2015/12/creating-high-resolution-integrated.html http://www.righto.com/2015/12/creating-high-resolution-integ... Home decapping is possible, from what I can tell, but uses methods like “fuming nitric acid” and “blowtorch”, neither of which I would really want to experiment with right now. resilicon.reddit.com is becoming fairly active, if you have an interest.
kens 6y ago
These chip come in a ceramic package, so decapping is a simple matter of tapping along the seam with a chisel. If you want high-quality die photos, you'll need a metallurgical microscope, which shines the light down through the lens. I got my microscope on eBay. Once you have a bunch of die photos, you can stitch them together with a program such as Hugin.

userbinator 6y ago

A lot of special-purpose ICs are actually general-purpose processors with a mask ROM (or sometimes EEPROM, with interesting consequences), since writing the "firmware" for different functionality is easier than doing a whole "hard-coded" chip design --- the various USB-to-X adapters are one common example of this.

737maxtw 6y ago
A large number of Realtek products are some form of MIPS core (or at least used to be).
segfaultbuserr 6y ago
A few days ago, I brought an USB-to-serial chip made by an obscure manufacturer. I found the RX/TX ports were working but control signals were not, I poked around the chip with an oscilloscope and found those pins were high-impedance, the chip didn't even attempt to output anything. I contacted tech support. They told me to buy a new one because my chip was an old batch without this feature (I guess it's a bug), but they can also provide a firmware update to me under NDA. It's microcontroller all the way down. Fun fact: It's also how those fake FTDI FT232 chips on the gray market were made. Counterfeiters just picked a cheap general-purpose microcontroller in mass production and wrote a Mask ROM for it. What's funny is that, the counterfeit chips actually have better process node than the real one (it doesn't mean it's better, though). https://zeptobars.com/en/read/FTDI-FT232RL-real-vs-fake-supereal https://zeptobars.com/en/read/FTDI-FT232RL-real-vs-fake-supe...
- marcan_42 6y ago
  They are better though: the clones fixed bugs that the original FTDIs had (bugs bad enough to make certain modes completely useless). https://twitter.com/marcan42/status/695292366639378433?s=19 https://twitter.com/marcan42/status/695292366639378433?s=19 Don't buy FTDI chips; their malicious driver incident that bricked clones (by exploiting another bug in the EEPROM write support in their own chips!) should be enough to convince every board designer to stay away from them.

mrlonglong 6y ago

Got one of these in my Beeb, never knew it was a dual core monster. No bloody wonder they were so expensive back in the day.