University of Central Florida
School of Electrical Engineering & Computer Science
COP 3402: System Software
Fall 2007
Homework #1 (P-Machine)
Due Sept 17, 2007 by 11:59 p.m.
The P-machine:
In this assignment you have to implement an interpreter for a virtual machine known as the
P-machine (PM/0). The interpreter must describe a stack machine, consisting of a store
named โstackโ organized as a stack and a โcodeโ store that contains the instructions. The
CPU has four registers: register โbpโ points to the base of the current activation record in
the stack, register โspโ points to the top of the stack, a program counter (pc) and an
instruction register (ir).
The ISA of the PM/0 has 22 instructions and the instruction format has three components
<OP, L, M>:
OP is the operation code.
Lindicates the lexicographical level.
Mdepending of the operators it indicates:
- A number (instructions: LIT, INT).
- A program address (instructions: JMP, JPC, CAL).
- A data address (instructions: LOD, STO)
- The identity of the operator OPR(i.e. OPR 0, 2 (ADD) or OPR 0, 4 (MUL)).
The machine has two cycles known as fetch and execute.
Fetch cycle:
In the fetch cycle an instruction is fetch from the code store (ir ๏ code[pc]) and the
program counter is incremented by one (pc ๏ pc + 1).
Execute cycle:
In this cycle ir.op indicates the operation to be executed. In case ir.op = OPR then the field
ir.m is used to identified the operator and execute the appropriate arithmetic or logical
instruction.
