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That AVR has 8-bit registers isn't much of a benefit today. While it might make the AVR's core small, it requires more instructions to operate on 16-bit or 32-b

That AVR has 8-bit registers isn't much of a benefit today. While it might make the AVR's core small, it requires more instructions to operate on 16-bit or 32-bit values — which a lot of code has to. For instance, an "int" in AVR C is 16 bits and because C does "integer promotion", it requires 16-bit semantics even when both operands are char. Despite having wider registers, I believe RISC-V cores could be made quite small too because of how lean its ISA is. As a hobbyist, I use AVR mostly because it is 5V-capable and electrically robust, so it can interface with vintage peripherals without requiring signal-level converters or additional ESD protection. It would be nice to see more competition in this space, for sure.

gsliepen 4y ago
While the C standard does say that integer promotion happens, if the result is being cast back to char again, a C compiler will see that it doesn't need to operate on 16 bits and is allowed to optimize the result back to 8 bit operations. See for example: https://godbolt.org/z/zM8reeqrc https://godbolt.org/z/zM8reeqrc
hajile 4y ago
I feel like 16-bit MCs aren't popular because they aren't popular. They offer a straight-up 2x performance increase in most applications and something like a 4-10x performance increase with 32-bit numbers (not to mention the space savings from fewer instructions). Despite this, the 16-bit MCs all seem to be rather niche. I'd love for an open RISC-V variant that could fill this gap and allow sourcing of the same ISA from multiple companies.