Added CNROM i.e. Mapper amhndu#3

Games like Adventure Island and Paperboy work.

include/Mapper.h

@@ -21,6 +21,7 @@ namespace sn
                 NROM = 0,
                 MMC1 = 1,
                 UxROM = 2,
+                CNROM = 3,
             };
 
             Mapper(Cartridge& cart, Type t) : m_cartridge(cart), m_type(t) {};

include/MapperCNROM.h

@@ -0,0 +1,23 @@
+#ifndef MAPPERCNROM_H
+#define MAPPERCNROM_H
+#include "Mapper.h"
+
+namespace sn
+{
+    class MapperCNROM : public Mapper
+    {
+        public:
+            MapperCNROM(Cartridge& cart);
+            void writePRG (Address addr, Byte value);
+            Byte readPRG (Address addr);
+            const Byte* getPagePtr(Address addr);
+
+            Byte readCHR (Address addr);
+            void writeCHR (Address addr, Byte value);
+        private:
+            bool m_oneBank;
+
+            Address m_selectCHR;
+    };
+}
+#endif // MAPPERCNROM_H

src/Mapper.cpp

@@ -1,12 +1,13 @@
 #include "Mapper.h"
 #include "MapperNROM.h"
 #include "MapperUxROM.h"
+#include "MapperCNROM.h"
 
 namespace sn
 {
     std::unique_ptr<Mapper> Mapper::createMapper(Mapper::Type mapper_t, sn::Cartridge& cart)
     {
-        std::unique_ptr<Mapper> ret;
+        std::unique_ptr<Mapper> ret(nullptr);
         switch (mapper_t)
         {
             case NROM:
@@ -15,8 +16,11 @@ namespace sn
             case UxROM:
                 ret.reset(new MapperUxROM(cart));
                 break;
+            case CNROM:
+                ret.reset(new MapperCNROM(cart));
+                break;
             default:
-                ret.reset(nullptr);
+                break;
         }
         return ret;
     }

src/MapperCNROM.cpp

@@ -0,0 +1,50 @@
+#include "MapperCNROM.h"
+#include "Log.h"
+
+namespace sn
+{
+    MapperCNROM::MapperCNROM(Cartridge &cart) :
+        Mapper(cart, Mapper::CNROM),
+        m_selectCHR(0)
+    {
+        if (cart.getROM().size() == 0x4000) //1 bank
+        {
+            m_oneBank = true;
+        }
+        else //2 banks
+        {
+            m_oneBank = false;
+        }
+    }
+
+    Byte MapperCNROM::readPRG(Address addr)
+    {
+        if (!m_oneBank)
+            return m_cartridge.getROM()[addr - 0x8000];
+        else //mirrored
+            return m_cartridge.getROM()[(addr - 0x8000) & 0x3fff];
+    }
+
+    void MapperCNROM::writePRG(Address addr, Byte value)
+    {
+        m_selectCHR = value & 0x3;
+    }
+
+    const Byte* MapperCNROM::getPagePtr(Address addr)
+    {
+        if (!m_oneBank)
+            return &m_cartridge.getROM()[addr - 0x8000];
+        else //mirrored
+            return &m_cartridge.getROM()[(addr - 0x8000) & 0x3fff];
+    }
+
+    Byte MapperCNROM::readCHR(Address addr)
+    {
+        return m_cartridge.getVROM()[addr | (m_selectCHR << 13)];
+    }
+
+    void MapperCNROM::writeCHR(Address addr, Byte value)
+    {
+        LOG(Info) << "Read-only CHR memory write attempt at " << std::hex << addr << std::endl;
+    }
+}