3 ms·
> The PPC ISA is huge, with a vast number of instructions (hundreds), which implies a lot of energy-sucking decoder circuitry -- and data path too. Not necessa
by RetroTechie 3y ago
> The PPC ISA is huge, with a vast number of instructions (hundreds), which implies a lot of energy-sucking decoder circuitry -- and data path too.
Not necessarily. It depends on how regular (orthogonal) the instruction formats are. Highly regular (few formats) = easy to decode even if there are many instructions.
But for example x86 has many different instruction formats and -lengths. Decoding all those does come at a cost.
RISC-V is very good in this regard. There's even "embedded" variants that drop half the register set (RV64E, which imho doesn't make much sense, and RV32E which does).
And there's some projects having a go at designing a 16-bit variety (to compete with legacy 8-bit ISAs perhaps?). Remains to be seen if that ever becomes a standard though.