[Solved] CMPE230Systems Programming Project 2 –

( This project can be implemented in groups of at most two students.)

This project is to be done with Python. In this project, you will implement (i) an assembler and (ii) an execution simulator for a hypothetical CPU called CPU230. CPU230 is illustrated in the following figure:

Each instruction has fixed length of 3 bytes with the following format:

Opcode	Adressing mode	Operand
6 bits	2 bits	16 bits

Addressing mode bits are as follows:

Bits(binary)	Addressing mode
00	operand is immediate data
01	operand is in given in the register
10	operand’s memory address is given in the register
11	operand is a memory address
Note that registers are represented as bit patterns (here given in hex): PC=0000, A=0001, B=0002, C=0003, D=0004, E=0005, S=0006.

Instructions are as follows:

Instruction	Instruction code (hex)	Operand	Meaning	Flags set
HALT	1		Halts the CPU.
LOAD	2	immediate memoryregister	Loads operand onto A .
STORE	3	memoryregister	Stores value in A to the operand.
ADD	4	immediate memoryregister	adds operand to A.	CF,SF, ZF
SUB	5	immediate memoryregister	subtracts operand from A.	CF,SF, ZF
INC	6	immediate	increments operand (equivalent to add 1)	SF, ZF, CF
		memoryregister
DEC	7	immediate memoryregister	decrements operand (equivalent to sub 1)	SF, ZF, CF
XOR	8	immediate memoryregister	Bitwise XOR operand with A and store result in A.	SF, ZF
AND	9	immediate memoryregister	Bitwise AND operand with A and store result in A.	SF, ZF
OR	A	immediate memoryregister	Bitwise OR operand with A and store result in A.	SF, ZF
NOT	B	immediate memoryregister	Take complement of the bits of the operand.	SF, ZF
SHL	C	register	Shift the bits of register one position to the left.	SF, ZF, CF
SHR	D	register	Shift the bits of register one position to the right.	SF, ZF
NOP	E		No operation.
PUSH	F	register	Push a word sized operand (two bytes) and update S by subtracting 2.
POP	10	register	Pop a word sized data (two bytes) into the operand and update S by adding 2.
CMP	11	immediate memoryregister	Perform comparison (AC-operand) and set flag accordingly.	SF, ZF, CF
JMP	12	immediate	Unconditional jump. Set PC to address.
JZ JE	13	immediate	Conditional jump. Jump to address (given as immediate operand) if zero flag is true.
JNZ JNE	14	immediate	Conditional jump. Jump to address (given as immediate operand) if zero flag is false.
JC	15	immediate	Conditional jump. Jump if carry flag is true.
JNC	16	immediate	Conditional jump. Jump if carry flag is false.
JA	17	immediate	Conditional jump. Jump if carry flag is false.
JAE	18	immediate	Conditional jump. Jump if above or equal.
JB	19	immediate	Conditional jump. Jump if below.
JBE	1A	immediate	Conditional jump. Jump if below or equal.
READ	1B	memoryregister	Reads a character into the operand.
PRINT	1C	immediate memoryregister	Prints the operand as a character.

Note that memory address can be given as [xxxx] or [r] where xxxx is a hexadecimal number or r where r is a register name.

Labels can also be used. A label: marks the address, xxxx, at the point it is defined. Wherever you use a label, you should substitute the marked address xxxx for the label.

The assembler you build will be called cpu230assemble and the execution simulator will be called cpu230exec. They will be used as follows. Suppose you are given a assembly program given in file prog.asm. The following command will assemble the program and produce the binary output prog.bin.

> cpu230assemble prog.asm

The following program will execute the binary

> cpu230exec prog.bin

The above process is illustrated in the example below:

Assembly source code: prog.asm	Assemble	Assembled program : prog.bin	Execute	Output
LOAD ‘A’ STORE C LOAD MYDATA STORE B LOAD 0004 STORE D LOOP1: PRINT C LOAD C STORE [B] INC C INC B INC B DEC D JNZ LOOP1 HALT MYDATA:	cpu230assemble prog.asm à	080041 0D0003 08002D 0D0002 080004 0D0004 710003 090003 0E0002 190003 190002 190002 1D0004 530012 040000	cpu230exec prog.bin à	A B C D

Note also that in the above example, ascii codes of ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’ are stored at the memory addresses 002D, 002F, 0031, 0033, 0035.