107 lines
2.8 KiB
C
107 lines
2.8 KiB
C
#include <stdint.h>
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typedef struct{
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uint32_t regs[32], pc;
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uint8_t* mem;
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}Cpu;
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const uint32_t MEM_OFFSET = 0x80000000;
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static inline uint8_t load8(const uint8_t* mem, const uint32_t addr){
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return mem[addr - MEM_OFFSET];
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}
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static inline uint16_t load16(const uint8_t* mem, const uint32_t addr){
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return *(uint16_t*)(mem + addr - MEM_OFFSET);
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}
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static inline uint32_t load32(const uint8_t* mem, const uint32_t addr){
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return *(uint32_t*)(mem + addr - MEM_OFFSET);
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}
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static inline void store8(uint8_t* mem, const uint32_t addr, const uint8_t val){
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mem[addr - MEM_OFFSET] = val;
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}
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static inline void store16(uint8_t* mem, const uint32_t addr,
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const uint16_t val){
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*(uint16_t*)(mem + addr - MEM_OFFSET) = val;
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}
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static inline void store32(uint8_t* mem, const uint32_t addr,
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const uint32_t val){
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*(uint32_t*)(mem + addr - MEM_OFFSET) = val;
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}
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void R_type(const uint8_t func3, const uint8_t func7, uint32_t regs[32],
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const uint8_t rd, const uint8_t rs1, const uint8_t rs2){
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switch(func3){
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case /*ADD/SUB*/ 0x0:
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if(func7 == /*ADD*/ 0x00) regs[rd] = regs[rs1] + regs[rs2];
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else if(func7 == /*SUB*/ 0x20) regs[rd] = regs[rs1] - regs[rs2];
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break;
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case /*SLL*/ 0x1: regs[rd] = regs[rs1] << (regs[rs2] & 0x1f); break;
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case /*SLT*/ 0x2: regs[rd] = (int32_t)regs[rs1] < (int32_t)regs[rs2]; break;
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case /*SLTU*/ 0x3: regs[rd] = regs[rs1] < regs[rs2]; break;
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case /*XOR*/ 0x4: regs[rd] = regs[rs1] ^ regs[rs2]; break;
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case /*SRL/SRA*/ 0x5:
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if(func7 == /*SRL*/ 0x00) regs[rd] = regs[rs1] >> (regs[rs2] & 0x1f);
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else if(func7 == /*SRA*/ 0x20){
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regs[rd] = (int32_t)regs[rs1] >> (regs[rs2] & 0x1f);
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}
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break;
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case /*OR*/ 0x6: regs[rd] = regs[rs1] | regs[rs2]; break;
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case /*AND*/ 0x7: regs[rd] = regs[rs1] & regs[rs2]; break;
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}
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}
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void L_type(const uint8_t func3, uint32_t regs[32], const uint8_t rd,
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const uint8_t* mem, const uint8_t rs1, const int16_t imm){
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switch(func3){
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case /*LB*/ 0x0:
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regs[rd] = (int32_t)(int8_t)load8(mem, regs[rs1] + (int32_t)imm);
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break;
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case /*LH*/ 0x1:
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regs[rd] = (int32_t)(int16_t)load16(mem, regs[rs1] + (int32_t)imm);
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break;
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case /*LW*/ 0x2: regs[rd] = load32(mem, regs[rs1] + (int32_t)imm); break;
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case /*LBU*/ 0x4: load8(mem, regs[rs1] + (int32_t)imm); break;
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case /*LHU*/ 0x5: load16(mem, regs[rs1] + (int32_t)imm); break;
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}
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}
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void step(Cpu* cpu){
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//fetch
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const uint32_t inst = load32(cpu->mem, cpu->pc);
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cpu->pc += 4;
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//decode
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#define opcode (inst & 0x7f)
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#define func3 (inst >> 12 & 0x7)
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#define func7 (inst >> 25 & 0x7f)
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#define rd (inst >> 7 & 0x1f)
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#define rs1 (inst >> 15 & 0x1f)
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#define rs2 (inst >> 20 & 0x1f)
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#define imm_I ((int32_t)inst >> 20)
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//execute
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cpu->regs[0] = 0;
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switch(opcode){
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case 0x03: L_type(func3, cpu->regs, rd, cpu->mem, rs1, imm_I); break;
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case 0x33: R_type(func3, func7, cpu->regs, rd, rs1, rs2); break;
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}
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}
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int main(){
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} |