implemented keypad

interpreter now passes Timendus' flags test

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 Interpreter.cpp DisplaySDL.cpp BuzzerSDL.cpp)
+add_executable(chocochip8 main.cpp Interpreter.cpp DisplaySDL.cpp BuzzerSDL.cpp CountdownTimerSDL.cpp KeypadSDL.cpp)
 target_link_libraries(chocochip8 SDL2::SDL2-static)

CountdownTimerSDL.cpp

@@ -0,0 +1,18 @@
+#include "CountdownTimerSDL.hpp"
+
+CountdownTimerSDL::CountdownTimerSDL(unsigned frequency):
+  mDesiredFrequency{frequency},
+  mSDLFrequency{SDL_GetPerformanceFrequency()},
+  mStartTime{0},
+  mStartValue{0} {}
+
+void CountdownTimerSDL::set(unsigned value) {
+  mStartTime = SDL_GetPerformanceCounter();
+  mStartValue = value;
+}
+
+unsigned CountdownTimerSDL::get() const {
+  Uint64 elapsedTime = SDL_GetPerformanceCounter() - mStartTime;
+  Uint64 elapsedTicks = (elapsedTime * mDesiredFrequency) / mSDLFrequency;
+  return elapsedTicks >= mStartValue ? 0 : mStartValue - elapsedTicks;
+}

CountdownTimerSDL.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <SDL2/SDL_timer.h>
+
+#include "Peripherals.hpp"
+
+class CountdownTimerSDL : public chocochip8::CountdownTimer {
+public:
+  CountdownTimerSDL(unsigned frequency); 
+  void set(unsigned value) override;
+  unsigned get() const override;
+private:
+  const Uint64 mDesiredFrequency;
+  const Uint64 mSDLFrequency;
+  Uint64 mStartTime;
+  Uint64 mStartValue;
+};

DisplaySDL.cpp

@@ -1,8 +1,13 @@
 #include "DisplaySDL.hpp"
+#include "Peripherals.hpp"
 
+#include <SDL2/SDL_surface.h>
 #include <stdexcept>
 
-DisplaySDL::DisplaySDL(int w, int h, uint32_t fgColor, uint32_t bgColor) {
+DisplaySDL::DisplaySDL(int w, int h, uint32_t fgColor, uint32_t bgColor):
+  mpFramebuffer{std::make_unique<Framebuffer>()},
+  mpDisplayState{std::make_unique<Framebuffer>()},
+  mDoClear{true} {
   // Create SDL Window
   mpWindow = SDL_CreateWindow(
     "ChocoChip-8",
@@ -35,43 +40,69 @@ DisplaySDL::~DisplaySDL() {
   SDL_DestroyWindow(mpWindow);
 }
 
-void DisplaySDL::updateWindow() const {
+void DisplaySDL::clear() {
+  for(auto &scanline : *mpFramebuffer) {
+    scanline.reset();
+  }
+  mDoClear = true;
+}
+
+int DisplaySDL::blit(const chocochip8::Scanline &spriteScanline, int y) {
+  using chocochip8::Scanline;
+  Scanline &targetScanline = mpFramebuffer->at(y);
+  bool collision = (spriteScanline & targetScanline).any();
+  targetScanline ^= spriteScanline;
+  return collision;
+}
+
+void DisplaySDL::updateWindow(bool doWindowUpdate) const {
+  using chocochip8::Scanline;
   SDL_Surface *pSurface = SDL_GetWindowSurface(mpWindow);
-  SDL_LockSurface(pSurface);
+  if(mDoClear) {
+    for(auto &scanline : *mpDisplayState) {
+      scanline.reset();
+    }
+    SDL_FillRect(pSurface, NULL, mBgColor);
+    mDoClear = false;
+    doWindowUpdate = true;
+  }
 
-  int fx, fy; // ChocoChip8 Framebuffer coordinates
+  for(int y = 0; y < mpFramebuffer->size(); y++) {
-  int sx, sy; // SDL Surface coordinates
+    Scanline &rNewScanline = (*mpFramebuffer)[y];
-  int lx, ly; // Last-used ChocoChip8 Framebuffer coordinates
+    Scanline &rOldScanline = (*mpDisplayState)[y];
-  Uint32 lc;  // Last-used SDL color
+    if(rNewScanline == rOldScanline) {
-  
+      // Skip scanlines that haven't changed since the last update
-  // Fill the entire SDL surface, one pixel at a time
+      continue;
-  lx = -1;
+    }
-  ly = -1;
-  for(sy = 0; sy < pSurface->h; sy++) {
-    for(sx = 0; sx < pSurface->w; sx++) {
-      // Map SDL surface coordinates to Chocochip8 Framebuffer coordinates
-      fx = sx * (double(chocochip8::gcWidth) / pSurface->w);
-      fy = sy * (double(chocochip8::gcHeight) / pSurface->h);
 
-      // Reuse color if this screen pixel maps to the same ChocoChip8 pixel as the last
+    for(int x = 0; x < rNewScanline.size(); x++) {
-      if(fx != lx || fy != ly) {
+      bool isSet = rNewScanline._Unchecked_test(x);
-        lx = fx;
+      bool wasSet = rOldScanline._Unchecked_test(x);
-        ly = ly;
+      if(isSet == wasSet) {
-        // Read Chocochip8 Framebuffer and choose appropriate color,
+        continue;
-        // note that the MSB of an scanline's bitset is the leftmost pixel.
-        lc = (mpFramebuffer->at(fy)[(chocochip8::gcWidth - 1) - fx] ? mFgColor : mBgColor);
       }
 
-      // Convert (x, y) indexes into SDL Surface pixel array index
+      // Map framebuffer pixel to SDL surface rectangle,
-      Uint32 *pPixel = static_cast<Uint32*>(static_cast<void*>(
+      // note that the MSB of an scanline's bitset is the leftmost pixel.
-          static_cast<char*>(pSurface->pixels)
+      int z = (chocochip8::gcWidth - 1) - x;
-          + sy * pSurface->pitch
+      int x1 = (      z * pSurface->w) / chocochip8::gcWidth;
-          + sx * pSurface->format->BytesPerPixel
+      int x2 = ((z + 1) * pSurface->w) / chocochip8::gcWidth;
-      ));
+      int y1 = (      y * pSurface->h) / chocochip8::gcHeight;
-      *pPixel = lc;
+      int y2 = ((y + 1) * pSurface->h) / chocochip8::gcHeight;
+      SDL_Rect rect;
+      rect.x = x1;
+      rect.y = y1;
+      rect.w = x2 - x1;
+      rect.h = y2 - y1;
+
+      Uint32 color = (isSet ? mFgColor : mBgColor);
+      SDL_FillRect(pSurface, &rect, color);
+      doWindowUpdate = true;
     }
   }
 
-  SDL_UnlockSurface(pSurface);
+  if(doWindowUpdate) {
-  SDL_UpdateWindowSurface(mpWindow);
+    *mpDisplayState = *mpFramebuffer;
+    SDL_UpdateWindowSurface(mpWindow);
+  }
 }

DisplaySDL.hpp

@@ -2,17 +2,25 @@
 
 #include "Peripherals.hpp"
 
+#include <array>
 #include <cstdint>
+#include <memory>
 #include <SDL2/SDL_video.h>
 
 class DisplaySDL : public chocochip8::Display {
 public:
-  DisplaySDL(int w, int h, uint32_t fgCol, uint32_t bgCol);
+  DisplaySDL(int w, int h, uint32_t fgCol = 0xffffff, uint32_t bgCol = 0x000000);
   ~DisplaySDL() override;
-  void updateWindow() const;
+  void clear() override;
+  int blit(const chocochip8::Scanline &scanline, int y) override;
+  void updateWindow(bool forceWindowUpdate = false) const;
 
 private:
+  using Framebuffer = std::array<chocochip8::Scanline, chocochip8::gcHeight>;
+  std::unique_ptr<Framebuffer> mpFramebuffer;
+  mutable std::unique_ptr<Framebuffer> mpDisplayState;
   SDL_Window *mpWindow;
   Uint32 mFgColor;
   Uint32 mBgColor;
+  mutable bool mDoClear;
 };

Interpreter.cpp

@@ -4,15 +4,62 @@
 
 namespace chocochip8 {
 
-Interpreter::Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad):
+// converts any 8-bit sprite row to its high-res 16-bit equivalent
+constexpr uint16_t gcvLowResToHighResRowLookupTable[256] = {
+  0x0000, 0x0003, 0x000C, 0x000F, 0x0030, 0x0033, 0x003C, 0x003F, 0x00C0, 0x00C3, 0x00CC, 0x00CF, 0x00F0, 0x00F3, 0x00FC, 0x00FF, 
+  0x0300, 0x0303, 0x030C, 0x030F, 0x0330, 0x0333, 0x033C, 0x033F, 0x03C0, 0x03C3, 0x03CC, 0x03CF, 0x03F0, 0x03F3, 0x03FC, 0x03FF, 
+  0x0C00, 0x0C03, 0x0C0C, 0x0C0F, 0x0C30, 0x0C33, 0x0C3C, 0x0C3F, 0x0CC0, 0x0CC3, 0x0CCC, 0x0CCF, 0x0CF0, 0x0CF3, 0x0CFC, 0x0CFF, 
+  0x0F00, 0x0F03, 0x0F0C, 0x0F0F, 0x0F30, 0x0F33, 0x0F3C, 0x0F3F, 0x0FC0, 0x0FC3, 0x0FCC, 0x0FCF, 0x0FF0, 0x0FF3, 0x0FFC, 0x0FFF, 
+  0x3000, 0x3003, 0x300C, 0x300F, 0x3030, 0x3033, 0x303C, 0x303F, 0x30C0, 0x30C3, 0x30CC, 0x30CF, 0x30F0, 0x30F3, 0x30FC, 0x30FF, 
+  0x3300, 0x3303, 0x330C, 0x330F, 0x3330, 0x3333, 0x333C, 0x333F, 0x33C0, 0x33C3, 0x33CC, 0x33CF, 0x33F0, 0x33F3, 0x33FC, 0x33FF, 
+  0x3C00, 0x3C03, 0x3C0C, 0x3C0F, 0x3C30, 0x3C33, 0x3C3C, 0x3C3F, 0x3CC0, 0x3CC3, 0x3CCC, 0x3CCF, 0x3CF0, 0x3CF3, 0x3CFC, 0x3CFF, 
+  0x3F00, 0x3F03, 0x3F0C, 0x3F0F, 0x3F30, 0x3F33, 0x3F3C, 0x3F3F, 0x3FC0, 0x3FC3, 0x3FCC, 0x3FCF, 0x3FF0, 0x3FF3, 0x3FFC, 0x3FFF, 
+  0xC000, 0xC003, 0xC00C, 0xC00F, 0xC030, 0xC033, 0xC03C, 0xC03F, 0xC0C0, 0xC0C3, 0xC0CC, 0xC0CF, 0xC0F0, 0xC0F3, 0xC0FC, 0xC0FF, 
+  0xC300, 0xC303, 0xC30C, 0xC30F, 0xC330, 0xC333, 0xC33C, 0xC33F, 0xC3C0, 0xC3C3, 0xC3CC, 0xC3CF, 0xC3F0, 0xC3F3, 0xC3FC, 0xC3FF, 
+  0xCC00, 0xCC03, 0xCC0C, 0xCC0F, 0xCC30, 0xCC33, 0xCC3C, 0xCC3F, 0xCCC0, 0xCCC3, 0xCCCC, 0xCCCF, 0xCCF0, 0xCCF3, 0xCCFC, 0xCCFF, 
+  0xCF00, 0xCF03, 0xCF0C, 0xCF0F, 0xCF30, 0xCF33, 0xCF3C, 0xCF3F, 0xCFC0, 0xCFC3, 0xCFCC, 0xCFCF, 0xCFF0, 0xCFF3, 0xCFFC, 0xCFFF, 
+  0xF000, 0xF003, 0xF00C, 0xF00F, 0xF030, 0xF033, 0xF03C, 0xF03F, 0xF0C0, 0xF0C3, 0xF0CC, 0xF0CF, 0xF0F0, 0xF0F3, 0xF0FC, 0xF0FF, 
+  0xF300, 0xF303, 0xF30C, 0xF30F, 0xF330, 0xF333, 0xF33C, 0xF33F, 0xF3C0, 0xF3C3, 0xF3CC, 0xF3CF, 0xF3F0, 0xF3F3, 0xF3FC, 0xF3FF, 
+  0xFC00, 0xFC03, 0xFC0C, 0xFC0F, 0xFC30, 0xFC33, 0xFC3C, 0xFC3F, 0xFCC0, 0xFCC3, 0xFCCC, 0xFCCF, 0xFCF0, 0xFCF3, 0xFCFC, 0xFCFF, 
+  0xFF00, 0xFF03, 0xFF0C, 0xFF0F, 0xFF30, 0xFF33, 0xFF3C, 0xFF3F, 0xFFC0, 0xFFC3, 0xFFCC, 0xFFCF, 0xFFF0, 0xFFF3, 0xFFFC, 0xFFFF
+};
+
+// 4x5 sprites for hex digits 0-F
+constexpr uint8_t gcvLowResFontData[80] = {
+  0xF0, 0x90, 0x90, 0x90, 0xF0,
+  0x20, 0x60, 0x20, 0x20, 0x70,
+  0xF0, 0x10, 0xF0, 0x80, 0xF0,
+  0xF0, 0x10, 0xF0, 0x10, 0xF0,
+  0x90, 0x90, 0xF0, 0x10, 0x10,
+  0xF0, 0x80, 0xF0, 0x10, 0xF0,
+  0xF0, 0x80, 0xF0, 0x90, 0xF0,
+  0xF0, 0x10, 0x20, 0x40, 0x40,
+  0xF0, 0x90, 0xF0, 0x90, 0xF0,
+  0xF0, 0x90, 0xF0, 0x10, 0xF0,
+  0xF0, 0x90, 0xF0, 0x90, 0x90,
+  0xE0, 0x90, 0xE0, 0x90, 0xE0,
+  0xF0, 0x80, 0x80, 0x80, 0xF0,
+  0xE0, 0x90, 0x90, 0x90, 0xE0,
+  0xF0, 0x80, 0xF0, 0x80, 0xF0,
+  0xF0, 0x80, 0xF0, 0x80, 0x80
+};
+
+Interpreter::Interpreter(Display &display, Buzzer &buzzer, Keypad &keypad, CountdownTimer &delayTimer, CountdownTimer &soundTimer):
   mvMemory(scMemorySize),
   mCallStack{},
   mrDisplay{display},
   mrBuzzer{buzzer},
   mrKeypad{keypad},
-  mcTicksPerSecond{ticksPerSecond},
+  mrDelayTimer(delayTimer),
+  mrSoundTimer(soundTimer),
   mvSpecialReg{},
-  mvReg{} {}
+  mvReg{},
+  mIsHighResMode{false} {
+  // Font sprite data goes into the interpreter reserved memory area
+  memcpy(mvMemory.data() + scLowRestFontAddr, gcvLowResFontData, sizeof(gcvLowResFontData));
+  // Initialize any non-zero registers at startup
+  mvSpecialReg[SR_PC] = scResetVector;
+}
 
 void Interpreter::tick() {
   // decodes all possible machine code arithmetic opcodes
@@ -24,13 +71,16 @@ void Interpreter::tick() {
   };
 
   // fetch instruction
-  sreg_t pc = mvSpecialReg[SR_PC];
+  sreg_t iInstAddr = mvSpecialReg[SR_PC];
-  unsigned inst = (mvMemory[pc] << 8) | mvMemory[pc + 1];
+  unsigned inst = (mvMemory.at(iInstAddr) << 8) | mvMemory.at(iInstAddr + 1);
+
+  // increment program counter
+  mvSpecialReg[SR_PC] += 2;
 
   // extract fields
-  unsigned regDst  = (inst & 0x0F00) >> 8; // destination register index
+  unsigned iRegDst = (inst & 0x0F00) >> 8; // destination register index
-  unsigned regSrc  = (inst & 0x00F0) >> 4; // source register index
+  unsigned iRegSrc = (inst & 0x00F0) >> 4; // source register index
-  unsigned opcode  = (inst & 0x000F);      // arithmetic opcode
+  unsigned opcode  = (inst & 0x000F);      // arithmetic opcode or sprite index
   unsigned imm8    = (inst & 0x00FF);      // 8-bit immediate
   unsigned imm12   = (inst & 0x0FFF);      // 12-bit immediate
 
@@ -38,9 +88,7 @@ void Interpreter::tick() {
   case 0x0000: // 0NNN - call machine language routine
     switch(inst) {
     case 0x00E0: // clear display
-      for(auto &scanline : *mrDisplay.mpFramebuffer) {
+      mrDisplay.clear();
-        scanline.reset();
-      }
       break;
     case 0x00EE: // return from subroutine
       mvSpecialReg[SR_PC] = mCallStack.top();
@@ -55,29 +103,29 @@ void Interpreter::tick() {
     mvSpecialReg[SR_PC] = imm12;
     break;
   case 0x2000: // 2NNN - call subroutine
-    mCallStack.push(pc);
+    mCallStack.push(mvSpecialReg[SR_PC]);
     mvSpecialReg[SR_PC] = imm12;
     break;
   case 0x3000: // 3XNN - skip if equal immediate
-    executeArithmetic(Opcode::JEQ, regDst, imm8);
+    executeArithmetic(Opcode::JEQ, iRegDst, imm8);
     break;
   case 0x4000: // 4XNN - skip if nonequal immediate
-    executeArithmetic(Opcode::JNEQ, regDst, imm8);
+    executeArithmetic(Opcode::JNEQ, iRegDst, imm8);
     break;
   case 0x5000: // 5XY0 - skip if equal
-    executeArithmetic(Opcode::JEQ, regDst, mvReg[regSrc]);
+    executeArithmetic(Opcode::JEQ, iRegDst, mvReg[iRegSrc]);
     break;
   case 0x6000: // 6XNN - load immediate
-    executeArithmetic(Opcode::SET, regDst, imm8);
+    executeArithmetic(Opcode::SET, iRegDst, imm8);
     break;
   case 0x7000: // 7XNN - increment
-    executeArithmetic(Opcode::ADD, regDst, imm8);
+    executeArithmetic(Opcode::ADD, iRegDst, imm8);
     break;
   case 0x8000: // 8XNN - general arithmetic
-    executeArithmetic(opcodeMap[opcode], regDst, mvReg[regSrc]); 
+    executeArithmetic(opcodeMap[opcode], iRegDst, mvReg[iRegSrc]); 
     break;
   case 0x9000: // 9XY0 - skip if nonequal
-    executeArithmetic(Opcode::JNEQ, regDst, mvReg[regSrc]);
+    executeArithmetic(Opcode::JNEQ, iRegDst, mvReg[iRegSrc]);
     break;
   case 0xA000: // ANNN - load I
     mvSpecialReg[SR_I] = imm12;
@@ -86,36 +134,89 @@ void Interpreter::tick() {
     mvSpecialReg[SR_I] = mvReg[R_V0] + imm12;
     break;
   case 0xC000: // CXNN - load random
-    executeArithmetic(Opcode::RAND, regDst, imm8);
+    executeArithmetic(Opcode::RAND, iRegDst, imm8);
     break;
   case 0xD000: // DXYN - draw
+    executeDraw(mvReg[iRegDst], mvReg[iRegSrc], opcode);
     break;
-  case 0xE000: // EX9E, EXA1 - keypad access
+  case 0xE000: // keypad access
+    switch(inst & 0xF0FF) {
+    case 0xE09E: // EX9E - skip if key pressed
+      if(mrKeypad.isKeyPressed(mvReg[iRegDst])) {
+        mvSpecialReg[SR_PC] += 2;
+      }
+      break;
+    case 0xE0A1: // EXA1 - skip if key not pressed
+      if(!mrKeypad.isKeyPressed(mvReg[iRegDst])) {
+        mvSpecialReg[SR_PC] += 2;
+      }
+      break;
+    default:
+      throw std::invalid_argument("not implemented");
+      break;
+    }
     break;
   case 0xF000: // several unique instructions
+    switch(inst & 0xF0FF) {
+    case 0xF007: // FX07 - read timer register
+      mvReg[iRegDst] = mrDelayTimer.get();
+      break;
+    case 0xF00A: // FX0A - wait for a keypress
+      mvSpecialReg[SR_PC] -= 2;
+      for(int i = KEY_0; i < KEY_0 + KEY_COUNT; i++) {
+        if(mrKeypad.isKeyPressed(i)) {
+          mvSpecialReg[SR_PC] += 2;
+          break;
+        }
+      }
+      break;
+    case 0xF015: // FX15 - set timer register
+      mrDelayTimer.set(mvReg[iRegDst]);
+      break;
+    case 0xF018: // FX18 - set sound timer register
+      if(mvReg[iRegDst] != 0) {
+        mrBuzzer.on();
+      }
+      mrSoundTimer.set(mvReg[iRegDst]);
+      break;
+    case 0xF01E: // FX1E - add to I
+      mvSpecialReg[SR_I] += mvReg[iRegDst];
+      break;
+    case 0xF029: // FX29 - set I to address of font sprite data for digit X
+      mvSpecialReg[SR_I] = scLowRestFontAddr + 5 * mvReg[iRegDst];
+      break;
+    case 0xF033: // FX33 - convert to bcd
+      mvMemory.at(mvSpecialReg[SR_I])     = (mvReg[iRegDst] / 100) % 10;
+      mvMemory.at(mvSpecialReg[SR_I] + 1) = (mvReg[iRegDst] / 10) % 10;
+      mvMemory.at(mvSpecialReg[SR_I] + 2) = mvReg[iRegDst] % 10;
+      break;
+    case 0xF055: // FX55 - dump registers
+      for(int i = 0; i <= iRegDst - R_V0; i++) {
+        mvMemory.at(mvSpecialReg[SR_I]++) = mvReg[R_V0 + i];
+      }
+      break;
+    case 0xF065: // FX65 - restore registers
+      for(int i = 0; i <= iRegDst - R_V0; i++) {
+        mvReg[R_V0 + i] = mvMemory.at(mvSpecialReg[SR_I]++);
+      }
+      break;
+    default:
+      throw std::invalid_argument("not implemented");
+      break;
+    }
     break;
   }
 
-  // increment PC
+  if(mrSoundTimer.get() == 0) {
-  mvSpecialReg[SR_PC] += 2;
+    mrBuzzer.off();
-
-  // decrement timers
-  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(size_t where, char const* data, size_t count) {
+void Interpreter::loadProgram(char const* data, size_t count, size_t where) {
   if(where + count > scMemorySize) {
     throw std::out_of_range("program exceeds memory bounds or capacity");
   }
-  memcpy(mvMemory.data(), data, count);
+  memcpy(mvMemory.data() + where, data, count);
 }
 
 void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
@@ -127,27 +228,30 @@ void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
   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] = operand << 1;
-    mvReg[iReg] <<= 1;
+    // VF = shifted out bit
+    mvReg[R_VF] = (operand & 0x80) ? 1 : 0;
     break;
   case Opcode::RSH:
-    mvReg[R_VF] = (mvReg[iReg] & 0x01) ? 1 : 0;
+    mvReg[iReg] = operand >> 1;
-    mvReg[iReg] >>= 1;
+    // VF = shifted out bit
+    mvReg[R_VF] = (operand & 0x01) ? 1 : 0;
     break;
   case Opcode::ADD:
-    tmp = mvReg[iReg] + operand;
+    mvReg[iReg] = mvReg[iReg] + operand;
-    mvReg[R_VF] = (tmp < mvReg[iReg]) ? 1 : 0;
+    // VF = 1 if carry occurs, VF = 0 if no carry
-    mvReg[iReg] = tmp;
+    mvReg[R_VF] = (mvReg[iReg] < operand) ? 1 : 0;
     break;
   case Opcode::SUB:
-    tmp = mvReg[iReg] - operand;
+    tmp = mvReg[iReg];
-    mvReg[R_VF] = (tmp > mvReg[iReg]) ? 1 : 0;
+    mvReg[iReg] = mvReg[iReg] - operand;
-    mvReg[iReg] = tmp;
+    // VF = 0 if borrow occurs, VF = 1 if no borrow
+    mvReg[R_VF] = (mvReg[iReg] > tmp) ? 0 : 1;
     break;
   case Opcode::SUB2:
-    tmp = operand - mvReg[iReg];
+    mvReg[iReg] = operand - mvReg[iReg];
-    mvReg[R_VF] = (tmp > operand) ? 1 : 0;
+    // VF = 0 if borrow occurs, VF = 1 if no borrow
-    mvReg[iReg] = tmp;
+    mvReg[R_VF] = (mvReg[iReg] > operand) ? 0 : 1;
     break;
   case Opcode::JEQ:
     if(mvReg[iReg] == operand) {
@@ -165,4 +269,58 @@ void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
   }
 }
 
+void Interpreter::executeDraw(uint8_t x, uint8_t y, uint8_t n) { 
+  size_t iMemAddr = mvSpecialReg[SR_I]; // address of the sprite data in memory
+  int collisionCount = 0; // number of scanlines in which any pixel changes from on to off
+
+  // coordinates are doubled in low resolution mode
+  if(!mIsHighResMode) {
+    x *= 2;
+    y *= 2;
+  }
+  x %= gcWidth;
+  y %= gcHeight;
+  // make x=0 be the right side of the screen instead of the left
+  x = gcWidth - x;
+
+  // draw each row of the sprite
+  for(int i = 0; i < (mIsHighResMode && n == 0 ? 16 : n); i++) {
+    uint16_t spriteRowBits;
+    if(mIsHighResMode) {
+      // draws an 8xN sprite
+      spriteRowBits = mvMemory.at(iMemAddr++) << 8;
+      if(n == 0) {
+        // draws an 16xN sprite, so fetch another byte from sprite data
+        spriteRowBits |= mvMemory.at(iMemAddr++);
+      }
+    } else {
+      // in low-res mode, each sprite pixel draws two on-screen pixels
+      spriteRowBits = gcvLowResToHighResRowLookupTable[mvMemory.at(iMemAddr++)];
+    }
+
+    // convert to bitset and shift into absolute horizontal position on the screen
+    Scanline spriteScanline(spriteRowBits);
+    if(x < 16) {
+      spriteScanline >>= (16 - x);
+    } else {
+      spriteScanline <<= (x - 16);
+    }
+
+    // we draw one scanline per sprite row in high-res mode, but twice in low-res mode
+    for(int j = 0; j < (mIsHighResMode ? 1 : 2); j++) {
+      // blit the sprite bitset into the screen
+      if(mrDisplay.blit(spriteScanline, y + i * (mIsHighResMode ? 1 : 2) + j) != 0) {
+        collisionCount += 1;
+      }
+    }
+
+    // update state flags
+    if(mIsHighResMode) {
+      mvReg[R_VF] = collisionCount;  
+    } else {
+      mvReg[R_VF] = (collisionCount > 0 ? 1 : 0);
+    }
+  }
+}
+
 }; // namespace chochochip8 

Interpreter.hpp

@@ -14,6 +14,7 @@ private:
   using sreg_t = unsigned;
 
 public:
+  constexpr static sreg_t scLowRestFontAddr = 0x0000;
   constexpr static sreg_t scResetVector = 0x0200;
   constexpr static size_t scMemorySize = 4096;
 
@@ -24,7 +25,7 @@ public:
   };
 
   enum {
-    SR_PC, SR_I, SR_T1, SR_T2,
+    SR_PC, SR_I, /*SR_T1, SR_T2,*/
     SR_COUNT
   };
 
@@ -33,12 +34,13 @@ public:
   };
 
 public:
-  Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad);
+  Interpreter(Display &display, Buzzer &buzzer, Keypad &keypad, CountdownTimer &delayTimer, CountdownTimer &soundTimer);
   void tick();
-  void loadProgram(size_t where, char const* data, size_t count);
+  void loadProgram(char const* data, size_t count, size_t where = scResetVector);
 
 private:
   void executeArithmetic(Opcode opcode, int iReg, reg_t operand);
+  void executeDraw(uint8_t x, uint8_t y, uint8_t n);
 
 private:
   std::vector<uint8_t> mvMemory;
@@ -46,9 +48,11 @@ private:
   Display &mrDisplay;
   Buzzer &mrBuzzer;
   Keypad &mrKeypad;
-  const unsigned mcTicksPerSecond;
+  CountdownTimer &mrDelayTimer;
+  CountdownTimer &mrSoundTimer;
   sreg_t mvSpecialReg[SR_COUNT];
   reg_t mvReg[R_COUNT];
+  bool mIsHighResMode;
 }; // class Interpreter
 
 }; // namespace chocohip8

KeypadSDL.cpp

@@ -0,0 +1,36 @@
+#include "KeypadSDL.hpp"
+
+bool KeypadSDL::isKeyPressed(int key) const {
+  return mvKeyDown.at(key);
+}
+
+void KeypadSDL::processEvent(SDL_Event &e) {
+  auto keymap = [](int sdlKeyCode) -> int {
+    switch(sdlKeyCode) {
+      case SDLK_1: return chocochip8::KEY_1;
+      case SDLK_2: return chocochip8::KEY_2;
+      case SDLK_3: return chocochip8::KEY_3; 
+      case SDLK_4: return chocochip8::KEY_C;
+      case SDLK_q: return chocochip8::KEY_4;
+      case SDLK_w: return chocochip8::KEY_5;
+      case SDLK_e: return chocochip8::KEY_6;
+      case SDLK_r: return chocochip8::KEY_D;
+      case SDLK_a: return chocochip8::KEY_7;
+      case SDLK_s: return chocochip8::KEY_8;
+      case SDLK_d: return chocochip8::KEY_9;
+      case SDLK_f: return chocochip8::KEY_E;
+      case SDLK_z: return chocochip8::KEY_A;
+      case SDLK_x: return chocochip8::KEY_0;
+      case SDLK_c: return chocochip8::KEY_B;
+      case SDLK_v: return chocochip8::KEY_F;
+      default    : return -1;
+    }
+  };
+
+  if(e.type == SDL_KEYUP || e.type == SDL_KEYDOWN) {
+    int k = keymap(e.key.keysym.sym);
+    if(k != -1) {
+      mvKeyDown[k] = (e.type == SDL_KEYDOWN);
+    }
+  }
+}

KeypadSDL.hpp

@@ -0,0 +1,12 @@
+#include "Peripherals.hpp"
+
+#include <SDL2/SDL_events.h>
+#include <array>
+
+class KeypadSDL : public chocochip8::Keypad {
+public:
+  bool isKeyPressed(int key) const override;
+  void processEvent(SDL_Event &e);
+private:
+  std::array<bool, chocochip8::KEY_COUNT> mvKeyDown;
+};

Peripherals.hpp

@@ -1,30 +1,26 @@
 #pragma once
 
-#include <array>
 #include <bitset>
-#include <memory>
 
 namespace chocochip8 {
 
   constexpr size_t gcWidth = 128;
   constexpr size_t gcHeight = 64;
   using Scanline = std::bitset<gcWidth>;
-  using Framebuffer = std::array<Scanline, gcHeight>;
 
-  enum class Key {
+  enum {
     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
+    KEY_C, KEY_D, KEY_E, KEY_F,
+    KEY_COUNT
   };
 
   class Display {
   public:
-    friend class Interpreter;
-    Display(): mpFramebuffer{std::make_unique<Framebuffer>()} {}
     virtual ~Display() = default;
-  protected:
+    virtual int blit(const Scanline& spriteScanline, int y) = 0;
-    std::unique_ptr<Framebuffer> mpFramebuffer;
+    virtual void clear() = 0;
   };
 
   class Buzzer {
@@ -37,7 +33,14 @@ namespace chocochip8 {
   class Keypad {
   public:
     virtual ~Keypad() = default;
-    virtual void isKeyPressed(Key key) = 0;
+    virtual bool isKeyPressed(int key) const = 0;
+  };
+
+  class CountdownTimer {
+  public:
+    virtual ~CountdownTimer() = default;
+    virtual void set(unsigned value) = 0;
+    virtual unsigned get() const = 0;
   };
 
 }; // namespace chocochip8

main.cpp

@@ -1,36 +1,58 @@
 #include <iostream>
+#include <iterator>
+#include <fstream>
+#include <vector>
+
 #include <SDL2/SDL.h>
 
 #include "BuzzerSDL.hpp"
+#include "CountdownTimerSDL.hpp"
 #include "DisplaySDL.hpp"
-#include "Peripherals.hpp"
+#include "KeypadSDL.hpp"
+#include "Interpreter.hpp"
 
-int main(int argc, char* args[]) {
+int main(int argc, char* argv[]) {
   if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
     std::cerr << "Couldn't initialize SDL: " << SDL_GetError() << '\n';
     return 1;
   }
 
-  class DisplayTest : public DisplaySDL {
-  public:
-    DisplayTest() : DisplaySDL(1280, 640, 0xff0000, 0x00ff00) {
-      for(int i = 0; i < chocochip8::gcHeight; i+=2) {
-        mpFramebuffer->at(i).set();
-      }
-    }
-  };
-
   BuzzerSDL buzzer(440);
-  //buzzer.on();
+  int N = 4;
-  DisplayTest display;
+  DisplaySDL display(128*N, 64*N);
+  KeypadSDL keypad;
+  CountdownTimerSDL delayTimer(60);
+  CountdownTimerSDL soundTimer(60);
+  CountdownTimerSDL displayTimer(60);
+  chocochip8::Interpreter chip8(display, buzzer, keypad, delayTimer, soundTimer);
+
+  auto rom = std::vector<char>();
+  auto romfile = std::ifstream(argv[1] != NULL ? argv[1] : "/dev/stdin", std::ios_base::in | std::ios_base::binary);
+  std::copy(
+    std::istreambuf_iterator<char>(romfile),
+    std::istreambuf_iterator<char>(),
+    std::back_insert_iterator(rom)
+  );
+  chip8.loadProgram(rom.data(), rom.size());
 
   SDL_Event event;
-  while(SDL_WaitEvent(&event) && event.type != SDL_QUIT) {
+  bool done = false;
-    display.updateWindow();
+  while(!done) {
+    while(SDL_PollEvent(&event)) {
+      if(event.type == SDL_QUIT) {
+        done = true;
+      } else {
+        keypad.processEvent(event);
+      }
+    }
+    chip8.tick();
+    if(displayTimer.get() == 0) {
+      display.updateWindow();
+      displayTimer.set(1);
+    }
   }
   
   buzzer.off();
   SDL_Quit();
   return 0;
 }
-