#include
#include “shell.h”
#include
#include
#include
#include
uint8_t op;
uint32_t instruction;
uint32_t addr_rs, addr_rt, addr_rd;
uint32_t rs, rt, rd; //to save the register value
uint8_t func;
uint16_t itemp; //for save immidiate number
//please take a loot at https://inst.eecs.berkeley.edu/~cs61c/resources/MIPS_Green_Sheet.pdf
// or
// https://web.cse.ohio-state.edu/~crawfis.3/cse675-02/Slides/MIPS%20Instruction%20Set.pdf
void fetch()
{
printf(“fetch “);
instruction = mem_read_32(CURRENT_STATE.PC); //the instruction
NEXT_STATE.PC = CURRENT_STATE.PC + 4;
}
void decode()
{
//printf(“decode “);
op = instruction >> 26; //find the 31-26 bit
// printf(“the op: %x “,op);
// if op==0, it is R type
if (op == 0) {
addr_rs = (instruction >> 21) & 0x1f;
addr_rt = (instruction >> 16) & 0x1f;
addr_rd = (instruction >> 11) & 0x1f;
rs = CURRENT_STATE.REGS[addr_rs]; //2^5=32
rt = CURRENT_STATE.REGS[addr_rt];
// rd=CURRENT_STATE.REGS[addr_rd];
func = instruction & 0x3f;
}
if (op == 8) { //addi:001000
printf(“addi instruction \n”);
addr_rs = (instruction >> 21) & 0x1f;
addr_rt = (instruction >> 16) & 0x1f;
rs = CURRENT_STATE.REGS[addr_rs]; //2^5=32
itemp = instruction & 0x0000ffff;
if (itemp > 32767) { //2^15-1=32767 is the largest number
itemp = ~itemp + 1;
rt = rs – itemp;
}
else {
rt = rs + itemp;
}
NEXT_STATE.REGS[addr_rt] = rt; // It is fine if you just execute here instead of executing in execute() function.
}
}
void execute()
{
printf(“execute”);
if (op == 0) {
switch (func) {
case 32: //add:100000
printf(“add instruction \n”);
rd = 0;
// if(rt>2147483647)
rd = rt + rs;
NEXT_STATE.REGS[addr_rd] = rd;
break;
case 12: //system call:001100
if (CURRENT_STATE.REGS[2] == 10) { //v0==10 then exit
printf(“systemcall: exit\n”);
RUN_BIT = FALSE;
}
if (CURRENT_STATE.REGS[2] == 1) { //v0==1: print int
rt = CURRENT_STATE.REGS[4]; //a0 is 4th register
printf(“\n print the number: %d \n “, rt);
}
break;
default:
break;
}
}
}
void process_instruction()
{
/* execute one instruction here. You should use CURRENT_STATE and modify
* values in NEXT_STATE. You can call mem_read_32() and mem_write_32() to
* access memory. */
fetch();
decode();
execute();
}