I wouldn’t say it didn’t have any microcode. It actually had a small PLA for sequencing the multi-cycle instructions. [0]
I don’t think anyone would actually label it as microcode (not when the entire point of RISC was to avoid microcode) they would call it a sequencer or finite state machine; But really it’s the same thing. It’s certainly much simpler than the full microcode of any contemporary CISC, and the bulk of instructions execute in a single cycle without using it.
If you want a design with zero microcode, you really need to look at MIPS, or the original Berkeley RISC. Those ISAs go out of their way to avoid multicycle instructions. Not entirely successfully, but they don't use PLAs [1] to implement any state machines for the few remaining instructions like multiply and divide.
[1]At least on the few MIPS designs I've looked at.And I'm not sure if they deliberately avoided PLAs for doctrine reasons, or it was just more efficient to do so.
Yes, once the market came into existence, ARM was well situated to take advantage of it.
> all the commercial benefit
"All" is a tricky term to use here. They got some. An appreciable amount even. Their business model leaves quite a bit on the floor compared to desktop chips.
I wouldn’t say it didn’t have any microcode. It actually had a small PLA for sequencing the multi-cycle instructions. [0]
I don’t think anyone would actually label it as microcode (not when the entire point of RISC was to avoid microcode) they would call it a sequencer or finite state machine; But really it’s the same thing. It’s certainly much simpler than the full microcode of any contemporary CISC, and the bulk of instructions execute in a single cycle without using it.
If you want a design with zero microcode, you really need to look at MIPS, or the original Berkeley RISC. Those ISAs go out of their way to avoid multicycle instructions. Not entirely successfully, but they don't use PLAs [1] to implement any state machines for the few remaining instructions like multiply and divide.
[0] http://daveshacks.blogspot.com/2016/01/inside-armv1-instruct...
[1] At least on the few MIPS designs I've looked at. And I'm not sure if they deliberately avoided PLAs for doctrine reasons, or it was just more efficient to do so.
Yet their purity brought them no commercial benefit.
ARM got all the commercial benefit once they switched from making chips to providing full designs ready to integrate into other chips.
> to providing full designs ready to integrate
Yes, once the market came into existence, ARM was well situated to take advantage of it.
> all the commercial benefit
"All" is a tricky term to use here. They got some. An appreciable amount even. Their business model leaves quite a bit on the floor compared to desktop chips.