Teodor-Dumitru Ene has been doing some interesting work on optimising hardware adders. Until I spoke with him, I didn’t realise how important this basic digital building block really is. An interesting statistic from his presentation slides: When a RISC-V processor boots into Linux, 65% to 72% of instructions use addition. By default, Yosys will synthesise something like this: reg [31:0] a; reg [31:0] b; wire sum = a + b; Using a ‘middle of the road’ adder, that gives medium PPA (power,...
