[libre-riscv-dev] morphing 6600 code to use power decoder

[Luke Kenneth Casson Leighton <lkcl@lkcl.net>]

i'm making a start on linking up the 6600 experimental code with the power
isa decoder based on microwatt.

given that the 6600 code already was in an "internal opcode" format very
similar in principle to microwatt, this _should_ be relatively
straightforward.

i will start with the CompUnit for fixed integer ALUs, keeping it simple
and passing over cherry picked decoded fields.

however one key difference will be that whilst immediates are read from the
opcode, registers are *not* immediately read from the regfile, they are
done by way of a regfile port bus, and only when available are "latched"
into registers.

only when all read regs become available can the op proceed.

so it is a little different from microwatt which just does, in sequence,
decode read execute write.

it should be fine.

l.



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