started work on the CHIP-8 interpreter

2024-11-26 06:52:49 -05:00
parent 3e5da27250
commit 7069e0ae49
7 changed files with 270 additions and 16 deletions
--- a/Interpreter.cpp
+++ b/Interpreter.cpp
@@ -0,0 +1,160 @@
+#include "Interpreter.hpp"
+#include <cstring>
+#include <stdexcept>
+
+namespace chocochip8 {
+
+Interpreter::Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad):
+  mvMemory(scMemorySize),
+  mCallStack{},
+  mrDisplay{display},
+  mrBuzzer{buzzer},
+  mrKeypad{keypad},
+  mcTicksPerSecond{ticksPerSecond},
+  mvSpecialReg{},
+  mvReg{} {}
+
+void Interpreter::tick() {
+  constexpr Opcode opcodeMap[16] = {
+    Opcode::SET, Opcode::OR,  Opcode::AND, Opcode::XOR,
+    Opcode::ADD, Opcode::SUB, Opcode::RSH, Opcode::SUB2,
+    Opcode::UNIMPL, Opcode::UNIMPL, Opcode::UNIMPL, Opcode::UNIMPL,
+    Opcode::UNIMPL, Opcode::UNIMPL, Opcode::LSH, Opcode::UNIMPL,
+  };
+
+  unsigned pc = mvSpecialReg[SR_PC];
+  unsigned inst = (mvMemory[pc] << 8) | mvMemory[pc + 1];
+  unsigned reg1 = (inst & 0x0F00) >> 8;
+  unsigned reg2 = (inst & 0x00F0) >> 4;
+  unsigned imm1 = (inst & 0x000F);
+  unsigned imm2 = (inst & 0x00FF);
+  unsigned imm3 = (inst & 0x0FFF);
+
+  mvSpecialReg[SR_PC] += 2;
+  switch(inst & 0xF000) {
+  case 0x0000: // 0NNN - call machine language routine
+    if(inst == 0x00E0) {
+      // clear display
+      for(auto &scanline : *mrDisplay.mpFramebuffer) {
+        scanline.reset();
+      }
+    } else if(inst == 0x00EE) {
+      // return from subroutine
+      mvSpecialReg[SR_PC] = mCallStack.top();
+      mCallStack.pop();
+    } else {
+      throw std::invalid_argument("not implemented");
+    }
+    break;
+  case 0x1000: // 1NNN - unconditional jump
+    mvSpecialReg[SR_PC] = imm3;
+    break;
+  case 0x2000: // 2NNN - call subroutine
+    mCallStack.push(pc);
+    mvSpecialReg[SR_PC] = imm3;
+    break;
+  case 0x3000: // 3XNN - skip if equal immediate
+    executeArithmetic(Opcode::JEQ, reg1, imm2);
+    break;
+  case 0x4000: // 4XNN - skip if nonequal immediate
+    executeArithmetic(Opcode::JNEQ, reg1, imm2);
+    break;
+  case 0x5000: // 5XY0 - skip if equal
+    executeArithmetic(Opcode::JEQ, reg1, mvReg[reg2]);
+    break;
+  case 0x6000: // 6XNN - load immediate
+    executeArithmetic(Opcode::SET, reg1, imm2);
+    break;
+  case 0x7000: // 7XNN - increment
+    executeArithmetic(Opcode::ADD, reg1, imm2);
+    break;
+  case 0x8000: // 8XNN - general arithmetic
+    executeArithmetic(opcodeMap[imm1], reg1, mvReg[reg2]); 
+    break;
+  case 0x9000: // 9XY0 - skip if nonequal
+    executeArithmetic(Opcode::JNEQ, reg1, mvReg[reg2]);
+    break;
+  case 0xA000: // ANNN - load I
+    mvSpecialReg[SR_I] = imm3;
+    break;
+  case 0xB000: // BNNN - jump indirect
+    mvSpecialReg[SR_I] = mvReg[R_V0] + imm3;
+    break;
+  case 0xC000: // CXNN - load random
+    executeArithmetic(Opcode::RAND, reg1, imm2);
+    break;
+  case 0xD000: // DXYN - draw
+    break;
+  case 0xE000: // EX9E, EXA1 - keypad access
+    break;
+  case 0xF000: // several unique instructions
+    break;
+  }
+
+  if(mvSpecialReg[SR_T1] > 0) {
+    mvSpecialReg[SR_T1] -= 1;
+  }
+
+  if(mvSpecialReg[SR_T2] > 0) {
+    mvSpecialReg[SR_T2] -= 1;
+    if(mvSpecialReg[SR_T2] == 0) {
+      mrBuzzer.off();
+    }
+  }
+}
+
+void Interpreter::loadProgram(uint16_t where, char const* data, size_t count) {
+  if(where + count > scMemorySize) {
+    throw std::out_of_range("program exceeds memory bounds or capacity");
+  }
+  memcpy(mvMemory.data(), data, count);
+}
+
+void Interpreter::executeArithmetic(Opcode opcode, int iReg, uint8_t operand) {
+  uint8_t tmp;
+  switch(opcode) {
+  case Opcode::SET:  mvReg[iReg]  = operand; break;
+  case Opcode::AND:  mvReg[iReg] &= operand; break;
+  case Opcode::OR:   mvReg[iReg] |= operand; break;
+  case Opcode::XOR:  mvReg[iReg] ^= operand; break;
+  case Opcode::RAND: mvReg[iReg]  = rand() & operand; break;
+  case Opcode::LSH:
+    mvReg[R_VF] = (mvReg[iReg] & 0x80) ? 1 : 0;
+    mvReg[iReg] <<= 1;
+    break;
+  case Opcode::RSH:
+    mvReg[R_VF] = (mvReg[iReg] & 0x01) ? 1 : 0;
+    mvReg[iReg] >>= 1;
+    break;
+  case Opcode::ADD:
+    tmp = mvReg[iReg] + operand;
+    mvReg[R_VF] = (tmp < mvReg[iReg]) ? 1 : 0;
+    mvReg[iReg] = tmp;
+    break;
+  case Opcode::SUB:
+    tmp = mvReg[iReg] - operand;
+    mvReg[R_VF] = (tmp > mvReg[iReg]) ? 1 : 0;
+    mvReg[iReg] = tmp;
+    break;
+  case Opcode::SUB2:
+    tmp = operand - mvReg[iReg];
+    mvReg[R_VF] = (tmp > operand) ? 1 : 0;
+    mvReg[iReg] = tmp;
+    break;
+  case Opcode::JEQ:
+    if(mvReg[iReg] == operand) {
+      mvSpecialReg[SR_PC] += 2;
+    }
+    break;
+  case Opcode::JNEQ:
+    if(mvReg[iReg] != operand) {
+      mvSpecialReg[SR_PC] += 2;
+    }
+    break;
+  case Opcode::UNIMPL:
+    throw std::invalid_argument("invalid opcode");
+    break;
+  }
+}
+
+}; // namespace chochochip8