cMips

by Cris Ghiurea

Compiler/Simulation

https://c3cris.github.io/cmips

CMips is a proof of concept of a 16 bit subset of MIPS designed by Cris Ghiurea ( c3cris ). cMips contains most features of a full working CPU using RISC design with a 32 by 32 bit monitor.

Included in the repo you will find an assembler for easy programming. It also contains demo code to get you started or you can use the web interface to assemble your own application.

Screenshot

JS Assembler for the CPU

https://c3cris.github.io/cmips/

Example

The Fibonacci sequence in cMips Assembly

addi  $1 $0 1     # a = 1
addi  $2 $0 0     # b = 0
loop:
    addi $3 $1 0  # c = a
    add $1 $1 $2  # a = a + b
    addi $2 $3 0  # b = c
jump loop         # jump to loop

c equivalent:

int a = 1;
int b = 0;
int c = 0;
while (true){
  c = a;
  a = a + b;
  b = c;
}

Binary:

0100000001000001
0100000010000000
0100001011000000
0000001010001000
0100011010000000
1011000000000010

OP Codes and Registers

https://github.com/c3cris/cmips/wiki

cMips has 3 types of instruction formats R, I and J in 16 bit:

Type	15-12	11-9	8-6	5-3	2-0
R	op	r1	r2	r3	f
I	op	r1	r2	#	#
J	op	#	#	#	#

op = op code of the instruction
r1 = register 1 bit | source reg
r2 = register 2 bit | target/source
r3 = register 3 bit | destination in R type
# = immediate bit

T	Code		1	2	3	4	5 - 10	11	12	13	14	15	16
R	ADD	0
R	SUB	0											1
R	ADDU	0										1
R	SUBU	0										1	1
R	AND	0									1
R	OR	0									1		1
R	NOR	0									1	1
R	XOR	0									1	1	1
R	SLL	1				1
R	SRL	1				1							1
R	SRA	1				1						1
R	SLLR	1				1
R	SRLR	1				1
R	SLT	1				1
R	SLTU	1				1
R	JR	1				1
R	MULT	2			1
R	MULTU	2			1								1
R	DIV	2			1							1
R	DIVU	2			1							1	1
R	MFHI	2			1						1
R	MFLO	2			1						1		1
R		2			1						1	1
R		2			1						1	1	1
R		3			1	1
R		3			1	1							1
R		3			1	1						1
R		3			1	1						1	1
R		3			1	1					1
R		3			1	1					1		1
R		3			1	1					1	1
R		3			1	1					1	1	1
I	ADDI	4		1				64	-	-	-	-	-
I	ADDIU	5		1		1		64	-	-	-	-	-
I	SUBIU	6		1	1			64	-	-	-	-	-
I	SLTI	7		1	1	1		64	-	-	-	-	-
I	SLTIU	8	1					64	-	-	-	-	-
I	LHW	9	1			1		64	-	-	-	-	-
I	SHW	10	1		1			64	-	-	-	-	-
J	J	11	1		1	1	4096 -	-	-	-	-	-	-
J	JAL	12	1	1			4096 -	-	-	-	-	-	-
I	BE	13	1	1		1	-	64	-	-	-	-	-
I	BNE	14	1	1	1		-	64	-	-	-	-	-
I	Syscall	15	1	1	1	1	-

• Empty commands are unused opcodes for future implementation.

Registers:

#	Name	Type
0	$0	zero
1	$1	general
2	$2	general
3	$3	general
4	$4	general
5	$5/v	general
6	$sp/6	stack pointer
7	$ra/7	return address

Installation

Simulator

This repo uses logisim-win-2.7.1.exe simulator which can be found at: https://sourceforge.net/projects/circuit/files/

Circuit

cMips.circ is the main logism file containing the CPU.

Rom Programs

• draw_checkers.dat
  • Demonstates writing to the simulated monitor
• fib.dat
  • Calculates fibinacci's sequence until it overflows
• mult_12345.dat
  • A demo of multiplication by addition.

cMips Dependencies

• Jquery 2.2.4 (included)
• Code Mirror
  • Install using npm install codemirror