69 lines
1.9 KiB
C
69 lines
1.9 KiB
C
#include <stdint.h>
|
|
|
|
typedef struct{
|
|
uint32_t regs[32], pc;
|
|
uint8_t* mem;
|
|
}Cpu;
|
|
|
|
const uint32_t MEMORY_OFFSET = 0x80000000;
|
|
|
|
static inline uint32_t load32(const uint8_t* memory, const uint32_t addr){
|
|
return *(uint32_t*)(memory + addr - MEMORY_OFFSET);
|
|
}
|
|
|
|
static inline uint32_t select_bits(const uint32_t val, const uint8_t end,
|
|
const uint8_t start){
|
|
|
|
const uint8_t len = end - start + 1;
|
|
return val >> start & (1 << len - 1);
|
|
}
|
|
|
|
void R_type(const uint8_t func3, const uint8_t func7, uint32_t regs[32],
|
|
const uint8_t rd, const uint8_t rs1, const uint8_t rs2){
|
|
|
|
switch(func3){
|
|
case /*ADD/SUB*/ 0x0:
|
|
if(func7 == /*ADD*/ 0x00) regs[rd] = regs[rs1] + regs[rs2];
|
|
else if(func7 == /*SUB*/ 0x20) regs[rd] = regs[rs1] - regs[rs2];
|
|
break;
|
|
|
|
case /*SLL*/ 0x1: regs[rd] = regs[rs1] << (regs[rs2] & 0x1f); break;
|
|
case /*SLT*/ 0x2: regs[rd] = (int32_t)regs[rs1] < (int32_t)regs[rs2]; break;
|
|
case /*SLTU*/ 0x3: regs[rd] = regs[rs1] < regs[rs2]; break;
|
|
case /*XOR*/ 0x4: regs[rd] = regs[rs1] ^ regs[rs2]; break;
|
|
|
|
case /*SRL/SRA*/ 0x5:
|
|
if(func7 == /*SRL*/ 0x00) regs[rd] = regs[rs1] >> (regs[rs2] & 0x1f);
|
|
else if(func7 == /*SRA*/ 0x20) regs[rd] = (int32_t)regs[rs1] >> (regs[rs2] & 0x1f);
|
|
break;
|
|
|
|
case /*OR*/ 0x6: regs[rd] = regs[rs1] | regs[rs2]; break;
|
|
case /*AND*/ 0x7: regs[rd] = regs[rs1] & regs[rs2]; break;
|
|
}
|
|
}
|
|
|
|
void step(Cpu* cpu){
|
|
//instruction fetch
|
|
const uint32_t inst = load32(cpu->mem, cpu->pc);
|
|
cpu->pc += 4;
|
|
|
|
//instruction decoding
|
|
#define opcode select_bits(inst, 6, 0)
|
|
#define func3 select_bits(inst, 14, 12)
|
|
#define func7 select_bits(inst, 31, 25)
|
|
#define rd select_bits(inst, 11, 7)
|
|
#define rs1 select_bits(inst, 19, 15)
|
|
#define rs2 select_bits(inst, 24, 20)
|
|
|
|
//execute
|
|
switch(opcode){
|
|
case /*R-type*/ 0x33: R_type(func3, func7, cpu->regs, rd, rs1, rs2); break;
|
|
//case /*I-type*/ 0x03: I_type(); break;
|
|
//case /*S-type*/ 0x23: S_type(); break;
|
|
//case /*B-type*/ 0x63: B_type(); break;
|
|
}
|
|
}
|
|
|
|
int main(){
|
|
|
|
} |