More PPU code

src/Ppu.cpp

@@ -6,7 +6,7 @@
 
 namespace nes {
 
-    Ppu::Ppu(): _column{}, _scanline{} {
+    Ppu::Ppu(): _column{}, _scanline{}, _status{} {
         _frameBuffer = std::make_unique<Pixel[]>(SCREEN_WIDTH*SCREEN_HEIGHT);
     }
 
@@ -32,11 +32,19 @@ namespace nes {
     }
 
     void Ppu::write(uint16_t address, uint8_t value) {
-
+        switch (address) {
+            default:
+                break;
+        }
     }
 
     uint8_t Ppu::read(uint16_t address) {
-        return 0;
+        switch (address) {
+            case Status:
+                uint8_t value = _status.value & 0xE0;
+                _status.verticalBlank = 0;
+                return value;
+        }
     }
 
     void Ppu::setPixel(uint16_t row, uint16_t column, Pixel pixel) {

src/Ppu.h

@@ -23,6 +23,27 @@ namespace nes {
         static constexpr uint16_t SCREEN_WIDTH = 256;
         static constexpr uint16_t SCREEN_HEIGHT = 240;
 
+        enum ControlAddress: uint16_t {
+            Control     = 0x0000,
+            Mask        = 0x0001,
+            Status      = 0x0002,
+            OamAddress  = 0x0003,
+            OamData     = 0x0004,
+            Scroll      = 0x0005,
+            PpuAddress  = 0x0006,
+            PpuData     = 0x0007
+        };
+
+        union StatusRegister {
+            struct {
+                uint8_t unused: 5;
+                uint8_t spriteOverflow: 1;
+                uint8_t spriteZeroHit: 1;
+                uint8_t verticalBlank: 1;
+            };
+            uint8_t value;
+        };
+
     public:
         Ppu();
         void tick();
@@ -36,6 +57,7 @@ namespace nes {
     private:
         int16_t _column;
         int16_t _scanline;
+        StatusRegister _status;
         std::unique_ptr<Pixel[]> _frameBuffer;
     };