4 ms·

Thanks, I understand that microcode is one of two ways to implement the control unit on a CPU. My question was more of if a CPU only has "a spartan eight hardwa

Thanks, I understand that microcode is one of two ways to implement the control unit on a CPU. My question was more of if a CPU only has "a spartan eight hardware instructions" and microcode is used to implement each of those eight hardware instructions how does that allow the ISA to be greater than the original eight instructions?

menage 6y ago
The microcode here consists of sequences of the eight low-level gigatron hardware instructions, which implement the richer 6502 ISA.
- bogomipz 6y ago
  Thanks for the insight. That makes sense. Cheers.
EvanAnderson 6y ago
The microcoded CPU is processing a richer virtual ISA. Have a look at SWEET16 for an analogous 16-bit virtual CPU on an 8-bit CPU: https://en.m.wikipedia.org/wiki/SWEET16 https://en.m.wikipedia.org/wiki/SWEET16 Edit: SWEET16 would run fine on this emulated 6502, too. Inception! The Apollo guidance computer did something similar.
- bogomipz 6y ago
  Very interesting link. I hadn't seen this before, this helps. Thanks.
- compressedgas 6y ago
  Also Dann McCreary wrote in 1978 an “8080 Simulator for the 6502” https://www.pagetable.com/?p=824 https://www.pagetable.com/?p=824
  - EvanAnderson 6y ago
    I now want to use the Javascript-based Gigatron emulator[1] in a browser on a Windows 2000 VM under the jslinux emulator[2]. (I wonder how jslinux would handle a few-year-old version of Firefox...) Then I can run the Gigatron-based 6502 emulator in that browser to run the 8080 simulator you referenced to run CP/M. Under CP/M I should be able to find a COBOL program to run. I would be achieving an immense coefficient-of-"Inception" and re-enacting "The Birth and Death of all Software" [3] simultaneously. Doing all of this in Windows NT 4.0 or Linux on my DEC Multia w/ an Alpha CPU would just be icing on the cake. [1] https://github.com/kervinck/gigatron-rom/tree/master/Contrib/PhilThomas https://github.com/kervinck/gigatron-rom/tree/master/Contrib... [2] https://bellard.org/jslinux/ https://bellard.org/jslinux/ [3] https://www.destroyallsoftware.com/talks/the-birth-and-death-of-javascript https://www.destroyallsoftware.com/talks/the-birth-and-death...

menage 6y ago

The microcode here consists of sequences of the eight low-level gigatron hardware instructions, which implement the richer 6502 ISA.

bogomipz 6y ago
Thanks for the insight. That makes sense. Cheers.

EvanAnderson 6y ago

The microcoded CPU is processing a richer virtual ISA. Have a look at SWEET16 for an analogous 16-bit virtual CPU on an 8-bit CPU: https://en.m.wikipedia.org/wiki/SWEET16 https://en.m.wikipedia.org/wiki/SWEET16 Edit: SWEET16 would run fine on this emulated 6502, too. Inception! The Apollo guidance computer did something similar.

bogomipz 6y ago
Very interesting link. I hadn't seen this before, this helps. Thanks.
compressedgas 6y ago
Also Dann McCreary wrote in 1978 an “8080 Simulator for the 6502” https://www.pagetable.com/?p=824 https://www.pagetable.com/?p=824
- EvanAnderson 6y ago
  I now want to use the Javascript-based Gigatron emulator[1] in a browser on a Windows 2000 VM under the jslinux emulator[2]. (I wonder how jslinux would handle a few-year-old version of Firefox...) Then I can run the Gigatron-based 6502 emulator in that browser to run the 8080 simulator you referenced to run CP/M. Under CP/M I should be able to find a COBOL program to run. I would be achieving an immense coefficient-of-"Inception" and re-enacting "The Birth and Death of all Software" [3] simultaneously. Doing all of this in Windows NT 4.0 or Linux on my DEC Multia w/ an Alpha CPU would just be icing on the cake. [1] https://github.com/kervinck/gigatron-rom/tree/master/Contrib/PhilThomas https://github.com/kervinck/gigatron-rom/tree/master/Contrib... [2] https://bellard.org/jslinux/ https://bellard.org/jslinux/ [3] https://www.destroyallsoftware.com/talks/the-birth-and-death-of-javascript https://www.destroyallsoftware.com/talks/the-birth-and-death...