3 ms·

I suspect that at the time microcode was copyrightable while masks (and therefore PLAs) were not (note the actual (C) message on the die explicitly calling out

I suspect that at the time microcode was copyrightable while masks (and therefore PLAs) were not (note the actual (C) message on the die explicitly calling out the microcode)

pwg 6y ago
In the context of IC chip layouts, the determining factor is almost always die area. Some functions will be smaller on the die in PLA form, other functions will be smaller on the die in microcode form. Since die area is almost always a scarce resource, the chip designer will usually pick the design that reduces die area consumption for any given function.
- Taniwha 6y ago
  (puts on chip designer hat) yes and no, as I said upstream the copyright laws of the time did not protect designs, chip copying (stealing) was rampant. I can imagine that some CPU designers from a particular world view (especially in the 70s) might only design in terms of microcode - but also design tools were pretty minimal, I can imagine that it might have been far easier to design things in terms of microcode rather than as PLAs - what you might be seeing here is the differences between different teams' in house custom tooling
- deleted 6y ago
  [deleted]
kens 6y ago
Protection for "mask works" was introduced in the Semiconductor Chip Protection act of 1984. You'll see a circled-M on modern dies indicating this protection. (I got the mask work symbol added to Unicode recently, but font support is lacking: 🆭.) The 8086 is the only chip I've seen with a copyright specifically designating the microcode.
miohtama 6y ago
Is 8086 microcode reverse engineered or released today for studying?
- Taniwha 6y ago
  probably not, but the data from this project should make that pretty easy However to be useful you need to know what each of those 21-bits is connected to, some will essentially be risc-like uCode instructions, the others will be tied to particular functions in the CPU or memory interface
- deleted 6y ago
  [deleted]
- kiwidrew 6y ago
  Not yet, but with these new high-resolution die photos it is only a matter of time. Meanwhile the US4449184 patent [1] referenced in the post's footnotes has a lot of information about how the microcode works (and the meaning of the 21 instruction bits) and, in Tables 7-12, shows the microcode listings for some of the microcoded 8086 instructions. [1] https://patents.google.com/patent/US4449184 https://patents.google.com/patent/US4449184

I suspect that at the time microcode was copyrightable while masks (and therefore PLAs) were not (note the actual (C) message on the die explicitly calling out the microcode)

pwg 6y ago

In the context of IC chip layouts, the determining factor is almost always die area. Some functions will be smaller on the die in PLA form, other functions will be smaller on the die in microcode form. Since die area is almost always a scarce resource, the chip designer will usually pick the design that reduces die area consumption for any given function.

Taniwha 6y ago
(puts on chip designer hat) yes and no, as I said upstream the copyright laws of the time did not protect designs, chip copying (stealing) was rampant. I can imagine that some CPU designers from a particular world view (especially in the 70s) might only design in terms of microcode - but also design tools were pretty minimal, I can imagine that it might have been far easier to design things in terms of microcode rather than as PLAs - what you might be seeing here is the differences between different teams' in house custom tooling
deleted 6y ago
[deleted]

kens 6y ago

Protection for "mask works" was introduced in the Semiconductor Chip Protection act of 1984. You'll see a circled-M on modern dies indicating this protection. (I got the mask work symbol added to Unicode recently, but font support is lacking: 🆭.) The 8086 is the only chip I've seen with a copyright specifically designating the microcode.

miohtama 6y ago

Is 8086 microcode reverse engineered or released today for studying?

Taniwha 6y ago
probably not, but the data from this project should make that pretty easy However to be useful you need to know what each of those 21-bits is connected to, some will essentially be risc-like uCode instructions, the others will be tied to particular functions in the CPU or memory interface
deleted 6y ago
[deleted]
kiwidrew 6y ago
Not yet, but with these new high-resolution die photos it is only a matter of time. Meanwhile the US4449184 patent [1] referenced in the post's footnotes has a lot of information about how the microcode works (and the meaning of the 21 instruction bits) and, in Tables 7-12, shows the microcode listings for some of the microcoded 8086 instructions. [1] https://patents.google.com/patent/US4449184 https://patents.google.com/patent/US4449184