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Re: New vax - implementation :-)

On Sat 03 Jul 2021 at 13:14:46 +0200, Anders Magnusson wrote:
> All of these steps are (mostly) independent of each other, therefore they
> can easily be pipelined.

Until you get to instructions with modify a register in one operand and
use it again in another :) such as (ok I took those examples from the
PDP-11 architecture handbook in the section where it describes how
different models do different things; but for a VAX you'd have to be
careful too and with 6 operands the number of combinations is much worse)

    ADD Rx,(Rx)+	; Rx gets incremented or not before being
    ADD Rx,@-(Rx)	;   used as a source operand
    MOV PC,offset(Rx)	; value of PC either before or after fetching
			;   offset from the instruction stream
    JMP (Rx)+		; Rx gets incremented or not before being
			;   copied to PC

and JMP is weird because it's more like a LEA arg,PC, if there were a
Load Effective Address instruction.

___ "Buying carbon credits is a bit like a serial killer paying someone else to
\X/  have kids to make his activity cost neutral." -The BOFH    falu.nl@rhialto

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