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laforest / Octavo

Verilog FPGA Parts Library. Old Octavo soft-CPU project.

Home Page:http://fpgacpu.ca/

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Detect no-op to raise Annul

laforest opened this issue · comments

commented

Currently, an annulled instruction gets turned into a no-op, by convention the all-zero instruction.

We should enable the reverse mapping: if the instruction is a no-op, then raise Annul.

The detector would be a set of all-zero detectors, with the sub-signal of D == 0 used to disable writes to A/B, enforcing the "read-only" behaviour of address 0.