path: root/src/ymh15/mips_cpu.cpp

#include "../../include/mips.h"
#include "mips_cpu_ymh15.hpp"

struct mips_cpu_impl {
    mips_mem_h mem;
    uint32_t regs[32];
    // lo and hi registers
    uint32_t lo, hi;
    // program counter
    uint32_t pc;
    // next pc used for branches and set the pc correctly
    uint32_t next_pc;
    // delay slot that makes branches work as expected
    uint32_t delay_slot;

    // sets the debug level so that you can print more information
    int debug_level;
    FILE *debug_type;
};

mips_cpu_h mips_cpu_create(mips_mem_h mem) {
    // creates new instance of a cpu explicitly
    mips_cpu_impl* state = new mips_cpu_impl;

    // reset all the variables
    state->mem = mem;
    state->pc = 0;
    state->next_pc = state->pc + 4;
    state->delay_slot = 0;
    state->lo = 0;
    state->hi = 0;
    
    state->debug_level = 0;
    state->debug_type = NULL;

    // sets all registers to 0
    for(int i = 0; i < 32; ++i) {
        state->regs[i] = 0;
    }

    return state;
}

mips_error mips_cpu_reset(mips_cpu_h state) {
    // resets both program counters
    state->pc = 0;
    state->next_pc = state->pc + 4;
    state->delay_slot = 0;
    state->hi = 0;
    state->lo = 0;

    // and registers
    for(int i = 0; i < 32; ++i) {
        state->regs[i] = 0;
    }

    return mips_Success;
}

mips_error mips_cpu_get_register(mips_cpu_h state, unsigned index,
                                 uint32_t *value) {
    // get the state of a current register by using the provided pointer;
    *value = state->regs[index];
    
    return mips_Success;
}

mips_error mips_cpu_set_register(mips_cpu_h state, unsigned index,
                                 uint32_t value) {
    if(index > 31 || index < 1) {
        return mips_ErrorInvalidArgument;
    }
    // set reg state
    state->regs[index] = value;
    
    return mips_Success;
}


mips_error mips_cpu_set_pc(mips_cpu_h state, uint32_t pc) {
    // set the pc and next_pc to the right values
    state->pc = pc;
    state->next_pc = state->pc+4;

    return mips_Success;
}

mips_error mips_cpu_get_pc(mips_cpu_h state, uint32_t *pc) {
    // get the value of the current pc
    *pc = state->pc;

    return mips_Success;
}

// This function executes the code that is found in memory at the address
// of the program counter
mips_error mips_cpu_step(mips_cpu_h state) {
    // gets the instruction from memory
    uint32_t inst;
    mips_mem_read(state->mem, state->pc, 4, (uint8_t*)&inst);
    
    // change the instruction back from big endian as it was read as little endian
    inst = (inst<<24) | ((inst>>8)&0xff00) | ((inst<<8)&0xff0000) | (inst>>24);

    // it then executes the instruction by decoding it first and returns
    // the state of the instruction
    mips_error mips_err = exec_instruction(state, inst);


    if(state->debug_level > 0) {
        fprintf(state->debug_type, "pc: %d\tpc_next: %d\tinst: %#10x\tdelay_slot: %d\n", state->pc, state->next_pc, inst, state->delay_slot);
    }

    // if the debug level is 2 or higher it will print the register state
    if(state->debug_level > 1) {
        fprintf(state->debug_type, "\nCPU register state:\n");
        for(unsigned i = 0; i < 32; ++i) {
            fprintf(state->debug_type, "R%d:\t%#10x\n", i,
                    state->regs[i]);
        }
        fprintf(state->debug_type, "\n\n");
    }

    if(state->debug_level > 2) {
        char c = getchar();
    }
    
    // it then updates the pc to next_pc which could have been changed
    // by a branch, it only does this if it is not in a delay slot   
    if(!state->delay_slot) {
        state->pc = state->next_pc;
        state->next_pc += 4;
    } else {
        state->pc += 4;
        --state->delay_slot;
    }

    // returns the operation error such as arithmetic overflow
    return mips_err;
}

mips_error mips_cpu_set_debug_level(mips_cpu_h state, unsigned level,
                                    FILE *dest) {
    if(!state) {
        return mips_ErrorInvalidArgument;
    }

    // just sets the cpu values for the debug level
    state->debug_level = level;
    state->debug_type = dest;
    
    return mips_Success;
}

void mips_cpu_free(mips_cpu_h state) {
    // deletes the state pointer of mips_cpu_impl* type
    if(state) {
        delete state;
    }
}

// The following functions are not present in the api as they are
// functions defined in a private header file

mips_error exec_instruction(mips_cpu_h state, uint32_t inst) {
    // creates var that holds all the information of the instruction
    uint32_t var[8];

    // prints pc and instruction every clock cycle
    
    for(int i = 0; i < 8; ++i) {
        var[i] = 0;
    }

    // decodes the instruction

    // if first 6 bits are 0 then it is a R instruction
    if(((inst >> 26)&0x3f) == 0) {
        // R Type: set all necessary variables
        var[REG_S] = inst >> 21;
        var[REG_T] = (inst >> 16)&0x1f;
        var[REG_D] = (inst >> 11)&0x1f;
        var[SHIFT] = (inst >> 6)&0x1f;
        var[FUNC] = inst&0x3f;

        // execute R instruction to perform operation
        return exec_R(state, var);
    } else if(((inst >> 26)&0x3f) == J || ((inst >> 26)&0x3f) == JAL) {    // as opcode is < 4
        var[OPCODE] = inst >> 26;           // it has to be J type
        var[MEM] = inst&0x3ffffff;
        return exec_J(state, var);
    } else {                                // otherwise it is an I type
        var[OPCODE] = inst >> 26;      
        var[REG_S] = (inst >> 21)&0x1f;
        var[REG_D] = (inst >> 16)&0x1f;
        var[IMM] = (uint32_t)(int16_t)(inst&0xffff);
        
        return exec_I(state, var);
    }
}

mips_error exec_R(mips_cpu_h state, uint32_t var[8]) {
    // if the function code is between 0x1f and 0x24 then it is addition
    // or subtraction
    if((var[FUNC]&0xf0) == ADD && (var[FUNC]&0xf) < 4) {
        // calls add with -1 if it is a subtractin and 1 if it is addition
        return add_sub(state, var, ((int32_t)-(var[FUNC]&0xf)/2)*2+1, 0);
        
    } else if((var[FUNC]&0xf0) == 0x20 && (var[FUNC]&0xf) < 7) {
        // else if the number is between 0x23 and 0x27 which means it
        // is a bitwise operation
        return bitwise(state, var, 0);
        
    } else if(var[FUNC] == JR) {
        // jr
        return jump(state, var, 0);
        
    } else if(var[FUNC] == JALR) {
        // jalr
        return jump(state, var, 1);
        
    } else if(var[FUNC] >= MFHI && var[FUNC] <= MTLO) {
        // mfhi mthi mflo mtlo
        return move(state, var);
        
    } else if(var[FUNC] >= MULT && var[FUNC] <= DIVU) {
        // mult multu div divu
        return mult_div(state, var);
        
    } else if(var[FUNC] == SLT || var[FUNC] == SLTU) {
        return set(state, var, 0);
        
    } else if(var[FUNC] == SLL || var[FUNC] == SLLV || var[FUNC] == SRA || var[FUNC] == SRAV || var[FUNC] == SRL || var[FUNC] == SRLV) {
        return shift(state, var);
        
    } else if(var[OPCODE] == 0 && var[REG_S] == 0 && var[REG_D] == 0 && var[REG_T] == 0 && var[SHIFT] == 0 && var[FUNC] == NOOP) {
        return mips_Success; 
        
    } else {
        // otherwise return that it was an invalid instruction
        return mips_ExceptionInvalidInstruction;
    }
}

mips_error exec_J(mips_cpu_h state, uint32_t var[8]) {
    switch(var[OPCODE]) {
    case J: // j
        return jump(state, var, 0);
    case JAL: // jal
        return jump(state, var, 1);
    default:
        return mips_ExceptionInvalidInstruction;
    }
}

mips_error exec_I(mips_cpu_h state, uint32_t var[8]) {
    switch(var[OPCODE]) {
    case BGEZ: // bgez, bgezal, bltz, bltzal
        return branch(state, var);
    case BEQ: // beq
        return branch(state, var);
    case BNE: // bne
        return branch(state, var);
    case BLEZ: // blez
        return branch(state, var); 
    case BGTZ: // bgtz
        return branch(state, var);
    case ADDI: // addi
        return add_sub(state, var, 1, 1);
    case ADDIU: // addiu
        return add_sub(state, var, 1, 2);
    case SLTI:
        return set(state, var, 1);
    case SLTIU:
        return set(state, var, 1);
    case ANDI:
        return bitwise(state, var, 1);
    case ORI: // ori
        return bitwise(state, var, 1);
    case XORI: // xori
        return bitwise(state, var, 1);
    case LUI: // lui
        return load(state, var);
    case LB: // lb
        return load(state, var);
    case LH: // lh
        return load(state, var);
    case LWL: // lwl
        return load(state, var);
    case LW: // lw
        return load(state, var);
    case LBU: // lbu
        return load(state, var);
    case LHU: // lhu
        return load(state, var);
    case LWR: // lwr
        return load(state, var);
    case SB: // sb
        return store(state, var);
    case SH: // sh
        return store(state, var);
    case SW: // sw
        return store(state, var);
    default:
        return mips_ExceptionInvalidInstruction;
    }
}

mips_error add_sub(mips_cpu_h state, uint32_t var[8], int32_t add_sub,
                   int32_t imm) {
    // sets initial values of the registers as local variables
    int32_t reg_s, reg_t, reg_d;

    // set the locals to the correct value from the register
    mips_cpu_get_register(state, var[REG_S], (uint32_t*)&reg_s);
    if(imm > 0) {
        reg_t = (int32_t)var[IMM];
    } else {
        mips_cpu_get_register(state, var[REG_T], (uint32_t*)&reg_t);
    }

    // perform the addition or subtraction
    reg_d = reg_s + add_sub*reg_t;

    // check for overflow conditions and if it is an unsigned operation
    if((var[FUNC]&0x1) == 1 || imm > 1 || !((reg_s > 0 && add_sub*reg_t > 0 && reg_d < 0) || (reg_s < 0 && add_sub*reg_t < 0 && reg_d > 0))) {

        // sets the destination register to the right answer
        mips_cpu_set_register(state, var[REG_D], (uint32_t)reg_d);
        return mips_Success;
    }
    
    return mips_ExceptionArithmeticOverflow;
}

mips_error bitwise(mips_cpu_h state, uint32_t var[8], unsigned imm) {
    // selects the right bitwise operation to perform then sets the register to the right value
    uint32_t reg_s, reg_t, reg_d;
    
    mips_cpu_get_register(state, var[REG_S], &reg_s);
    if(!imm) {
        mips_cpu_get_register(state, var[REG_T], &reg_t);
    } else {
        reg_t = var[IMM]&0x0000ffff;
    }

    // performs correct bitwise operation and sets register;
    if(var[FUNC] == AND || var[OPCODE] == ANDI) {
        reg_d = reg_s & reg_t;
    }
    else if(var[FUNC] == OR || var[OPCODE] == ORI) {
        reg_d = reg_s | reg_t;
    }
    else {
        reg_d = reg_s ^ reg_t;
    }

    // set register to the answer
    mips_cpu_set_register(state, var[REG_D], reg_d);
    
    return mips_Success;
}

mips_error branch(mips_cpu_h state, uint32_t var[8]) {
    if(var[OPCODE] == 1 && (var[REG_D] == 0x11 || var[REG_D] == 0x10)) {
        state->regs[31] = state->pc+8;
    }

    if((state->regs[var[REG_S]] == state->regs[var[REG_D]] && var[OPCODE] == BEQ) ||
       (state->regs[var[REG_S]] != state->regs[var[REG_D]] && var[OPCODE] == BNE) || 
       (((int32_t)state->regs[var[REG_S]] >= 0) && (var[OPCODE] == BGEZ) && (var[REG_D]&1) == 1) ||
       ((int32_t)state->regs[var[REG_S]] < 0 && var[OPCODE] == BLTZ && (var[REG_D]&1) == 0) ||
       ((int32_t)state->regs[var[REG_S]] > 0 && var[OPCODE] == BGTZ && (var[REG_D]&1) == 0) ||
       ((int32_t)state->regs[var[REG_S]] <= 0 && var[OPCODE] == BLEZ && (var[REG_D]&1) == 0)) {
        
        state->next_pc += (var[IMM]<<2);
        state->delay_slot += 1;
    }
    
    return mips_Success;
}

mips_error jump(mips_cpu_h state, uint32_t var[8], uint8_t link) {
    uint8_t reg_d;
    uint32_t jump_loc;
    if(var[FUNC] == JALR || var[FUNC] == JR) {
        jump_loc = state->regs[var[REG_S]];
        reg_d = var[REG_D];
        state->next_pc = jump_loc;
    } else {
        jump_loc = var[MEM]<<2;
        reg_d = 31;
        state->next_pc = (state->next_pc&0xf0000000) | (jump_loc&0xfffffff);
    }
    
    if(link) {
        state->regs[reg_d] = state->pc+8;
    }
    
    state->delay_slot += 1;

    return mips_Success;
}

mips_error load(mips_cpu_h state, uint32_t var[8]) {
    uint32_t addr = 0;
    uint8_t mem_byte = 0;
    uint16_t mem_halfword = 0;
    uint32_t mem_word = 0;
    unsigned i = 0;
    
    addr = state->regs[var[REG_S]] + var[IMM];

    if(var[OPCODE] == LB || var[OPCODE] == LBU) {
        mips_mem_read(state->mem, addr, 1, &mem_byte);
    } else if(var[OPCODE] == LH || var[OPCODE] == LHU) {
        if((addr&0b1) == 1) {
            return mips_ExceptionInvalidAlignment;
        }
        mips_mem_read(state->mem, addr, 2, (uint8_t*)&mem_halfword);
        mem_halfword = mem_halfword>>8 | mem_halfword<<8;
    } else if(var[OPCODE] == LW) {
        if((addr&0b1) == 1 || (addr&0b10)>>1 == 1) {
            return mips_ExceptionInvalidAlignment;
        }
        mips_mem_read(state->mem, addr, 4, (uint8_t*)&mem_word);
        mem_word = (mem_word<<24) | ((mem_word>>8)&0xff00) | ((mem_word<<8)&0xff0000) | (mem_word>>24);
    } else if(var[OPCODE] == LWL) {
        i = 3;
        while((addr&3) != 0) {
            mips_mem_read(state->mem, addr, 1, &mem_byte);
            mem_word = mem_word | ((uint32_t)mem_byte<<(i*8));
            ++addr;
            --i;
        }
    } else if(var[OPCODE] == LWR) {
        i = 0;
        while((addr&3) != 3) {
            mips_mem_read(state->mem, addr, 1, &mem_byte);
            mem_word = mem_word | ((uint32_t)mem_byte<<(i*8));
            --addr;
            ++i;
        }
    }
    
    switch(var[OPCODE]) {
    case LUI:
        state->regs[var[REG_D]] = var[IMM]<<16;
        return mips_Success;
    case LB:
        state->regs[var[REG_D]] = (uint32_t)(int8_t)mem_byte;
        return mips_Success;
    case LH:
        state->regs[var[REG_D]] = (uint32_t)(int16_t)mem_halfword;
        return mips_Success;
    case LWL:
        state->regs[var[REG_D]] = (state->regs[var[REG_D]]&(0xffffffff>>((3-i)*8))) | (mem_word&(0xffffffff<<((i+1)*8)));
        return mips_Success;
    case LW:
        state->regs[var[REG_D]] = mem_word;
        return mips_Success;
    case LBU:
        state->regs[var[REG_D]] = (uint32_t)mem_byte;
        return mips_Success;
    case LHU:
        state->regs[var[REG_D]] = (uint32_t)mem_halfword;
        return mips_Success;
    case LWR:
        state->regs[var[REG_D]] = (state->regs[var[REG_D]]&(0xffffffff<<(i*8))) | (mem_word&(0xffffffff>>((4-i)*8)));
        return mips_Success;
    default:
        return mips_ExceptionInvalidInstruction;
    }
}

mips_error store(mips_cpu_h state, uint32_t var[8]) {
    uint32_t addr;
    uint32_t word;
    uint16_t half_word;
    uint8_t byte;
    
    addr = state->regs[var[REG_S]] + var[IMM];
    word = state->regs[var[REG_D]];
    half_word = (uint16_t)state->regs[var[REG_D]];
    byte = (uint8_t)state->regs[var[REG_D]];
    
    if(var[OPCODE] == SB) {
        mips_mem_write(state->mem, addr, 1, &byte);
    } else if(var[OPCODE] == SH) {
        if((addr&0b1) == 1) {
            return mips_ExceptionInvalidAlignment;
        }
        uint16_t tmp = half_word << 8 | half_word >> 8;
        mips_mem_write(state->mem, addr, 2, (uint8_t*)&tmp);
    } else if(var[OPCODE] == SW) {
        if((addr&0b1) == 1 || (addr&0b10)>>1 == 1) {
            return mips_ExceptionInvalidAlignment;
        }
        uint32_t tmp = word<<24 | ((word>>8)&0xff00) | ((word<<8)&0xff0000) | word>>24;
        mips_mem_write(state->mem, addr, 4, (uint8_t*)&tmp);
    } else {
        return mips_ExceptionInvalidInstruction;
    }
    return mips_Success;
}

mips_error move(mips_cpu_h state, uint32_t var[8]) {
    switch(var[FUNC]) {
    case MFHI:
        return mips_cpu_set_register(state, var[REG_D], state->hi);
    case MTHI:
        return mips_cpu_get_register(state, var[REG_S], &state->hi);
    case MFLO:
        return mips_cpu_set_register(state, var[REG_D], state->lo);
    case MTLO:
        return mips_cpu_get_register(state, var[REG_S], &state->lo);
    default:
        return mips_ExceptionInvalidInstruction;
    }
    return mips_Success;
}

mips_error mult_div(mips_cpu_h state, uint32_t var[8]) {
    uint64_t unsigned_result, signed_result;
    switch(var[FUNC]) {
    case MULT: 
        signed_result = ((int64_t)(int32_t)state->regs[var[REG_S]])*((int64_t)(int32_t)state->regs[var[REG_T]]);
        state->lo = (uint32_t)signed_result;
        state->hi = (uint32_t)(signed_result>>32);
        return mips_Success;
        
    case MULTU:
        unsigned_result = ((uint64_t)state->regs[var[REG_S]])*((uint64_t)state->regs[var[REG_T]]);
        state->lo = (uint32_t)unsigned_result;
        state->hi = (uint32_t)(unsigned_result>>32);
        return mips_Success;
        
    case DIV:
        if(var[REG_T] == 0) {
            state->lo = 0;
            state->hi = 0;
            return mips_Success;
        }
        
        state->lo = ((int32_t)state->regs[var[REG_S]])/((int32_t)state->regs[var[REG_T]]);
        state->hi = ((int32_t)state->regs[var[REG_S]])%((int32_t)state->regs[var[REG_T]]);
        return mips_Success;
        
    case DIVU:
        if(var[REG_T] == 0) {
            state->lo = 0;
            state->hi = 0;
            return mips_Success;
        }
        
        state->lo = (state->regs[var[REG_S]])/(state->regs[var[REG_T]]);
        state->hi = (state->regs[var[REG_S]])%(state->regs[var[REG_T]]);
        return mips_Success;
        
    default:
        return mips_ExceptionInvalidInstruction;
    }
}

mips_error shift(mips_cpu_h state, uint32_t var[8]) {
    if(var[FUNC] == SLL && var[OPCODE] == 0) {
        state->regs[var[REG_D]] = state->regs[var[REG_T]] << var[SHIFT];
    } else if(var[FUNC] == SLLV) {
        state->regs[var[REG_D]] = state->regs[var[REG_T]] << state->regs[var[REG_S]];
    } else if(var[FUNC] == SRA) {
        state->regs[var[REG_D]] = (int32_t)state->regs[var[REG_T]] >> var[SHIFT];
    } else if(var[FUNC] == SRAV) {
        state->regs[var[REG_D]] = ((int32_t)state->regs[var[REG_T]]) >> state->regs[var[REG_S]];
    } else if(var[FUNC] == SRL) {
        state->regs[var[REG_D]] = state->regs[var[REG_T]] >> var[SHIFT];
    } else if(var[FUNC] == SRLV) {
        state->regs[var[REG_D]] = state->regs[var[REG_T]] >> state->regs[var[REG_S]];
    }
    return mips_Success;
}

mips_error set(mips_cpu_h state, uint32_t var[8], uint32_t imm) {
    uint32_t reg_s, reg_t, reg_d;

    mips_cpu_get_register(state, var[REG_S], &reg_s);
    
    if(!imm) {
        mips_cpu_get_register(state, var[REG_T], &reg_t);
    } else {
        reg_t = var[IMM];
    }

    if(var[FUNC] == SLT || var[OPCODE] == SLTI) {
        if(((int32_t)reg_s) < ((int32_t)reg_t)) {
            reg_d = 1;
        } else {
            reg_d = 0;
        }
    } else if(var[FUNC] == SLTU || var[OPCODE] == SLTIU) {
        if(reg_s < reg_t) {
            reg_d = 1;
        } else {
            reg_d = 0;
        }
    } else {
        return mips_ExceptionInvalidInstruction;
    }

    mips_cpu_set_register(state, var[REG_D], reg_d);

    return mips_Success;
}