3 ms·
Cute little cpu! I like the OPR instruction, neat way of handling increment/decrement (DEC by way of NOT and INC). Are ROR and ROL also chained? That's neat too
by beefok 10y ago
Cute little cpu!
I like the OPR instruction, neat way of handling increment/decrement (DEC by way of NOT and INC). Are ROR and ROL also chained? That's neat too.
- zenojevski 10y agoThanks! It is derived PDP-8's own OPR instruction, which goes even further, with many carefully aligned combinations leading to clever results. A testament of ingenuity which reveals fine craftsmanship. In reality, I've considered switching to a regular mapping, so to have 32 no-operand instructions instead, which would fit the original five operations, all sensible combinations, plus more. But chaining operands is definitely a more extravagant thing, so I think it can be instructive in showing how creative a solution can be in face of limitations .
- beefok 10y agoThe chaining kind of reminds me of how z80's ALU works [1]. It's kind of chained in together over time. [1] http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-h...