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>> engineering trade-offs Its not obvious what they trade off and got in return.
by frozenport 3y ago
>> engineering trade-offs
Its not obvious what they trade off and got in return.
- ksherlock 3y agoThe article mentions that ARM licensed SuperH patents for their Thumb instruction set, and ARM did that for improved code density, so that seems to be what they got in return. If you read through all 10 parts of the series, Raymond later mentions that it might look like a lot of code but instructions are half as big as other RISC contemporaries so it's better than it looks.
- zozbot234 3y ago> instructions are half as big as other RISC contemporaries That's a bit of a gimmick, tbh. Yes you can just about make it work if you have a really barebones insn set, as the early SuperH chips had. (You do need to start from a 2-register insn format of course.) But modern chips - even quite small chips nowadays - benefit from having more than that, so you're left with a really limited niche. (I do think that the calculus changes if you have a strictly Harvard architecture chip/core, since these might be able to afford a "weird" instruction length. A core with, e.g. 20-bit or 24-bit fixed-length instructions designed along the same lines gains some much needed space for ISA extension.)