Cpus »

Pdp 11 Recoding

Automatic recoding of PDP-11 Instructions into a "risc-line" Instruction Stream

After working on a simple direct decode PDP-11, and looking at the modern x86 architecture, and doing some work with "binary recompilation", it occured to me that it would be fun to try and create a machine to "recode" PDP-11 CISC instructions into a simple "risc like" instruction stream which could then be heavily pipelined with minimal hazards.

To that end I wrote a simple C language simulator which would read the PDP-11 instruction stream and perform the recoding. It works pretty well as a proof of concept.

Basically it boots and runs PDP-11 code by first "recoding" each instruction into a small bundle of "risc like" instructions.

An experiment in PDP-11 binary recoding