MMIX-SIM

Abstract

This program simulates a simplified version of the MMIX computer. Its main goal is to help people create and test MMIX programs for The Art of Computer Programming and related publications. It provides only a rudimentary terminal-oriented interface, but it has enough infrastructure to support a cool graphical user interface — which could be added by a motivated reader. (Hint, hint.)

MMIX is simplified in the following ways:

• There is no pipeline, and there are no caches. Thus, commands like SYNC and SYNCD and PREGO do nothing.

• Simulation applies only to user programs, not to an operating system kernel. Thus, all addresses must be nonnegative; “privileged” commands such as PUT rK,z or RESUME 1 or LDVTS x,y,z are not allowed; instructions should be executed only from addresses in segment 0 (addresses less than #2000000000000000). Certain special registers remain constant: rF = 0, rK = #ffffffffffffffff, rQ = 0; rT = #8000000500000000, rTT= #8000000600000000, rV=#369c200400000000.

• No trap interrupts are implemented, except for a few special cases of TRAP that provide rudimentary input-output.

• All instructions take a fixed amount of time, given by the rough estimates stated in the MMIX documentation. For example, MUL takes 10ν, LDB takes μ + ν; all times are expressed in terms of μ and ν, “mems” and “oops.” The simulated clock increases by 2³² for each μ and 1 for each ν. But the interval counter rI decreases by 1 for each ν; and the usage count field of rU may increase by 1 (modulo 2⁴⁷) for each instruction.