4 ms·
Many arm chips support both a RISC ISA (the original ARM), and a more CISC-y ISA (thumb2). They consume less power and perform better with the latter. So well,
by effn 16y ago
Many arm chips support both a RISC ISA (the original ARM), and a more CISC-y ISA (thumb2). They consume less power and perform better with the latter. So well, in fact, that some chips don't even bother with the legacy RISC mode.
- Aegean 16y agolegacy RISC mode? last time I checked it was called the ARM mode, which is the absolute standard. Thumb has benefits, but there are also limitations which is why I wouldn't call it a replacement.
- crnflke 16y agoNot anymore - Thumb2 is the new standard and supports everything that ARM does (at least, the last I read it did). One of the big differences is that you now need a marker instruction for predicated sequences, but obviously the encoding is quite different.
- darren_ 16y agoThumb and Thumb2 really aren't any more 'CISC'-y then ARM; about the most cisc aspect would be that thumb2 supports two different instruction lengths (2 and 4 byte) whereas ARM supports only 4 byte instructions. That said i've heard/read that Thumb2 tends to be the optimum size/space trade-off, but that's not because it's somehow more 'cisc'.