Implement address latch and ppu data/address registers

Jonazan2 · Oct 16, 2019 · b207b87 · b207b87
1 parent 83e00ab
commit b207b87
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Showing 5 changed files with 76 additions and 41 deletions.
diff --git a/Memory.cpp b/Memory.cpp
@@ -7,8 +7,9 @@
 #include "Video.h"
 
 
-Memory::Memory( const Cartridge *cartridge )
+Memory::Memory( const Cartridge *cartridge, Video *video )
     : cartridge( cartridge )
+    , video ( video )
 {
     map = new byte[ 64_KB ];
     Reset();
@@ -24,14 +25,47 @@ void Memory::Reset()
     memset( map, 0x00, 64_KB );
 
     MapCartridge();
+
+    map[ Video::PPUCTRL_REGISTER, 0x00 ];
+    map[ Video::PPUMASK_REGISTER, 0x00 ];
+    map[ Video::PPUSTATUS_REGISTER, 0b1010'0000 ];
+    map[ Video::OAMA_REGISTER, 0x00 ];
+    map[ Video::OAMADATA_REGISTER, 0x00 ];
+    map[ Video::PPUSCROLL_REGISTER, 0x00 ];
+    map[ Video::PPUDATA_ADDRESS, 0x00 ];
+}
+
+void Memory::MapCartridge()
+{
+    assert( cartridge != nullptr );
+
+    /* For now only support NROM with PRG ROM of 16KB and no ram */
+    Cartridge::Header header = cartridge->GetHeader();
+    assert( header.mapper == 0x00 && header.prgRomSizeKB == 16  && !header.hasPRGRam);
+
+    const byte * const rom = cartridge->GetRom();
+
+    /* Map the PRG ROM to 0x8000 */
+    memcpy(&map[0x8000], &rom[0x0010], 16_KB );
+
+    /* Mirror the PRG ROM in 0xC000 */
+    memcpy(&map[0xC000], &rom[0x0010], 16_KB );
 }
 
-byte Memory::Read( word address ) const
+byte Memory::Read( word address )
 {
     if ( address >= 0x2000 && address <= 0x3FFF )
     {
-        const word mirroredAddress = ( address % 8 ) + 0x2000;
-        return map[ mirroredAddress ];
+        const word ppuRegister = ( address % 8 ) + 0x2000;
+
+        if ( ppuRegister == Video::PPUSTATUS_REGISTER )
+        {
+            ResetAddressLatch();
+            const byte ppuStatus = map[ Video::PPUSTATUS_REGISTER ];
+            byte newPpuStatus = ppuStatus ^ 0b1000'0000;
+            Write( Video::PPUSTATUS_REGISTER, newPpuStatus );
+        }
+        return map[ ppuRegister ];
     }
     else
     {
@@ -43,8 +77,30 @@ void Memory::Write( word address, byte data )
 {
     if ( address >= 0x2000 && address <= 0x3FFF )
     {
-        const word mirroredAddress = ( address % 8 ) + 0x2000;
-        map[ mirroredAddress ] = data;
+        const word ppuRegister = ( address % 8 ) + 0x2000;
+        if ( ppuRegister == Video::PPUDATA_ADDRESS )
+        {
+            const word address = map[ Video::PPUADDR_REGISTER ];
+
+            if ( IsAddressLatchClear )
+            {
+                IsAddressLatchClear = false;
+                currentVRamAddress = ( data | currentVRamAddress ) << 8;
+            }
+            else
+            {
+                currentVRamAddress = data | currentVRamAddress;
+            }
+            map[ Video::PPUDATA_ADDRESS ] = data;
+
+            const byte ppuControlRegister = map[ Video::PPUCTRL_REGISTER ];
+            const byte incrementAmount = ( ppuControlRegister | 0b0000'0100 ) >> 2;
+            map[ Video::PPUADDR_REGISTER ] = incrementAmount;
+        }
+        else
+        {
+            map[ ppuRegister ] = data;
+        }
     }
     else
     {
@@ -57,19 +113,8 @@ const byte *const Memory::GetMemoryMap() const
     return map;
 }
 
-void Memory::MapCartridge()
+void Memory::ResetAddressLatch()
 {
-    assert( cartridge != nullptr );
-
-    /* For now only support NROM with PRG ROM of 16KB and no ram */
-    Cartridge::Header header = cartridge->GetHeader();
-    assert( header.mapper == 0x00 && header.prgRomSizeKB == 16  && !header.hasPRGRam);
-
-    const byte * const rom = cartridge->GetRom();
-
-    /* Map the PRG ROM to 0x8000 */
-    memcpy(&map[0x8000], &rom[0x0010], 16_KB );
-
-    /* Mirror the PRG ROM in 0xC000 */
-    memcpy(&map[0xC000], &rom[0x0010], 16_KB );
+    IsAddressLatchClear = true;
+    currentVRamAddress = 0x00;
 }
diff --git a/Memory.h b/Memory.h
@@ -41,13 +41,13 @@ class Memory
 {
 public:
 
-    Memory( const Cartridge *cartridge );
+    Memory( const Cartridge *cartridge, Video *video );
     ~Memory();
 
     void Reset();
 
     /* Memory management */
-    byte Read( word address ) const;
+    byte Read( word address );
     void Write( word address, byte data );
 
     const byte *const GetMemoryMap() const;
@@ -56,10 +56,14 @@ class Memory
 
     /* Associated NES systems */
     const Cartridge     *cartridge;
+    Video               *video;
 
     /* NES memory map */
     byte                *map;
 
+    bool                IsAddressLatchClear;
+    word                currentVRamAddress;
 
     void MapCartridge();
+    void ResetAddressLatch();
 };
diff --git a/Video.cpp b/Video.cpp
@@ -4,12 +4,10 @@
 #include <assert.h>
 
 #include "Cartridge.h"
-#include "Memory.h"
 
 
-Video::Video( Cartridge *cartridge, Memory *cpuMemory )
+Video::Video( Cartridge *cartridge )
     : cartridge( cartridge )
-    , cpuMemory( cpuMemory )
 {
     memory = new byte[ 16_KB ];
     frameBuffer = new RGB[ NES_VIDEO_RESOLUTION ];
@@ -35,14 +33,6 @@ void Video::Reset()
 
     MapCartridgeCHRToPPU();
 
-    cpuMemory->Write( PPUCTRL_REGISTER, 0x00 );
-    cpuMemory->Write( PPUMASK_REGISTER, 0x00 );
-    cpuMemory->Write( PPUSTATUS_REGISTER, 0b1010'0000 );
-    cpuMemory->Write( OAMA_REGISTER, 0x00 );
-    cpuMemory->Write( OAMADATA_REGISTER, 0x00 );
-    cpuMemory->Write( PPUSCROLL_REGISTER, 0x00 );
-    cpuMemory->Write( PPUADDR_REGISTER, 0x00 );
-    cpuMemory->Write( PPUDATA_ADDRESS, 0x00 );
 }
 
 void Video::MapCartridgeCHRToPPU()
@@ -55,8 +45,6 @@ void Video::MapCartridgeCHRToPPU()
     const u32 offset = (header.prgRomSizeKB * 1_KB) + 0x0010;
     const u32 dataSize = header.chrRomSizeKB * 1_KB;
     memcpy( memory, &cartridgeRom[ offset ], dataSize );
-
-    memory[ PPUSTATUS_REGISTER ] = 0b1010'0000;
 }
 
 RGB* Video::GetFrameBuffer() const
@@ -81,5 +69,5 @@ void Video::Write( word address, byte data )
 
 void Video::Update( u32 cycles )
 {
-
+    // We do nothing here for now
 }
diff --git a/Video.h b/Video.h
@@ -43,7 +43,6 @@
 
 
 class Cartridge;
-class Memory;
 
 class Video
 {
@@ -62,7 +61,7 @@ class Video
     static constexpr word PPUDATA_ADDRESS       = 0x2007;
 
 
-    Video( Cartridge *cartridge, Memory *cpuMemory );
+    Video( Cartridge *cartridge );
     ~Video();
 
     void Reset();
@@ -80,7 +79,6 @@ class Video
 private:
     /* Associated Systems */
     Cartridge       *cartridge;
-    Memory          *cpuMemory;
 
     /* PPU memory layout */
     byte            *memory;

diff --git a/main.cpp b/main.cpp
@@ -28,8 +28,8 @@ int main(int argc, char** argv)
 
     cartridge.PrintDetails();
 
-    Memory memory( &cartridge );
-    Video video( &cartridge, &memory );
+    Video video( &cartridge );
+    Memory memory( &cartridge, &video );
     Cpu cpu( &memory );
 
     Debugger debugger( &cpu, &memory, &video );