started work on the CHIP-8 interpreter

BuzzerSDL.cpp

@@ -1,15 +1,15 @@
-#include "Buzzer.hpp"
+#include "BuzzerSDL.hpp"
 
 #include <cmath>
 #include <limits>
 #include <stdexcept>
 #include <cstring>
 
-void SDLCALL Buzzer::audioCallback(void *userdata, Uint8 *stream, int len) {
-  static_cast<Buzzer*>(userdata)->copySamples(stream, len);
+void SDLCALL BuzzerSDL::audioCallback(void *userdata, Uint8 *stream, int len) {
+  static_cast<BuzzerSDL*>(userdata)->copySamples(stream, len);
 }
 
-Buzzer::Buzzer(unsigned buzzerFrequency) {
+BuzzerSDL::BuzzerSDL(unsigned buzzerFrequency) {
   SDL_AudioSpec desired;
   SDL_AudioSpec obtained;
 
@@ -42,19 +42,19 @@ Buzzer::Buzzer(unsigned buzzerFrequency) {
   miCurrentSample = 0;
 }
 
-Buzzer::~Buzzer() {
+BuzzerSDL::~BuzzerSDL() {
   SDL_CloseAudioDevice(mAudioDevice);
 }
 
-void Buzzer::on() {
+void BuzzerSDL::on() {
   SDL_PauseAudioDevice(mAudioDevice, SDL_FALSE);
 }
 
-void Buzzer::off() {
+void BuzzerSDL::off() {
   SDL_PauseAudioDevice(mAudioDevice, SDL_TRUE);
 }
 
-void Buzzer::copySamples(Uint8 *stream, int len) {
+void BuzzerSDL::copySamples(Uint8 *stream, int len) {
   // Copy len samples from the current position of the buffer,
   // looping back to the start of the buffer when needed.
   while(len > 0) {

BuzzerSDL.hpp

@@ -3,15 +3,17 @@
 #include <vector>
 #include <SDL2/SDL_audio.h>
 
-class Buzzer {
+#include "Peripherals.hpp"
+
+class BuzzerSDL : public chocochip8::Buzzer {
 public:
   using sample_t = Sint16;
 
-  Buzzer(unsigned frequency);
-  ~Buzzer();
+  BuzzerSDL(unsigned frequency);
+  ~BuzzerSDL();
 
-  void on();
-  void off();
+  void on() override;
+  void off() override;
 
 private:
   static void SDLCALL audioCallback(void *userdata, Uint8 *stream, int len);

CMakeLists.txt

@@ -5,5 +5,5 @@ SET(CMAKE_BUILD_TYPE Debug)
 add_subdirectory(submodules/sdl2)
 
 SET(CMAKE_EXPORT_COMPILE_COMMANDS ON)
-add_executable(chocochip8 main.cpp Buzzer.cpp)
+add_executable(chocochip8 main.cpp Interpreter.cpp BuzzerSDL.cpp)
 target_link_libraries(chocochip8 SDL2::SDL2-static)

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 

Interpreter.hpp

@@ -0,0 +1,51 @@
+#pragma once
+
+#include "Peripherals.hpp"
+
+#include <cstdint>
+#include <vector>
+#include <stack>
+
+namespace chocochip8 {
+
+class Interpreter {
+public:
+  constexpr static uint16_t scResetVector = 0x0200;
+  constexpr static size_t scMemorySize = 4096;
+
+private:
+  enum {
+    R_V0, R_V1, R_V2, R_V3, R_V4, R_V5, R_V6, R_V7,
+    R_V8, R_V9, R_VA, R_VB, R_VC, R_VD, R_VE, R_VF,
+    R_COUNT
+  };
+
+  enum {
+    SR_PC, SR_I, SR_T1, SR_T2,
+    SR_COUNT
+  };
+
+  enum class Opcode {
+    SET, ADD, SUB, SUB2, AND, OR, XOR, LSH, RSH, RAND, JEQ, JNEQ, UNIMPL
+  };
+
+public:
+  Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad);
+  void tick();
+  void loadProgram(uint16_t where, char const* data, size_t count);
+
+private:
+  void executeArithmetic(Opcode opcode, int iReg, uint8_t operand);
+
+private:
+  std::vector<uint8_t> mvMemory;
+  std::stack<uint16_t> mCallStack;
+  Display &mrDisplay;
+  Buzzer &mrBuzzer;
+  Keypad &mrKeypad;
+  const unsigned mcTicksPerSecond;
+  unsigned mvSpecialReg[SR_COUNT];
+  uint8_t mvReg[R_COUNT];
+}; // class Interpreter
+
+}; // namespace chocohip8

Peripherals.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <array>
+#include <bitset>
+#include <memory>
+
+namespace chocochip8 {
+
+  using Scanline = std::bitset<128>;
+  using Framebuffer = std::array<Scanline, 64>;
+
+  enum class Key {
+    KEY_0, KEY_1, KEY_2, KEY_3,
+    KEY_4, KEY_5, KEY_6, KEY_7,
+    KEY_8, KEY_9, KEY_A, KEY_B,
+    KEY_C, KEY_D, KEY_E, KEY_F
+  };
+
+  class Display {
+  public:
+    friend class Interpreter;
+    Display(): mpFramebuffer{std::make_unique<Framebuffer>()} {}
+    virtual ~Display() = default;
+  protected:
+    std::unique_ptr<Framebuffer> mpFramebuffer;
+  };
+
+  class Buzzer {
+  public:
+    virtual ~Buzzer() = default;
+    virtual void on() = 0;
+    virtual void off() = 0;
+  };
+
+  class Keypad {
+  public:
+    virtual ~Keypad() = default;
+    virtual void isKeyPressed(Key key) = 0;
+  };
+
+}; // namespace chocochip8

main.cpp

@@ -1,7 +1,7 @@
 #include <iostream>
 #include <SDL2/SDL.h>
 
-#include "Buzzer.hpp"
+#include "BuzzerSDL.hpp"
 
 int main(int argc, char* args[]) {
   if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
@@ -9,7 +9,7 @@ int main(int argc, char* args[]) {
     return 1;
   }
 
-  Buzzer buzzer(440);
+  BuzzerSDL buzzer(440);
   buzzer.on();
 
   SDL_Event event;