add memory mirroring for system and ppu memory

1 files changed, 14 insertions, 0 deletions

diff --git a/cpu.c b/cpu.c
index 8eaeff1..0fe6cbd 100644
--- a/cpu.c
+++ b/cpu.c
@@ -10,6 +10,12 @@
 #define STATUS_UPDATE_NEGATIVE(r)       \
         (regs.status.negative = ((r & (1 << 7)) > 0))
 
+#define MEMORY_MIRROR(addr)     \
+        if (addr < 0x2000)      \
+                addr &= 0x07FF; \
+        else if (addr < 0x4000) \
+                addr &= 0x2007;
+
 #define PUSH(b) \
         (memwrite(0x0100 + regs.sp--, b))
 #define PULL()  \
@@ -58,12 +64,16 @@ uint32_t cycles = 0;
 static uint8_t
 peek(uint16_t addr)
 {
+        MEMORY_MIRROR(addr);
+
         return memory[addr];
 }
 
 static uint16_t
 peek16(uint16_t addr)
 {
+        MEMORY_MIRROR(addr);
+
         /* bytes are stored in little-endian (low then high) */
         return (uint16_t)memory[addr] | ((uint16_t)memory[addr + 1] << 8);
 }
@@ -71,12 +81,16 @@ peek16(uint16_t addr)
 static void
 memwrite(uint16_t addr, uint8_t byte)
 {
+        MEMORY_MIRROR(addr);
+
         memory[addr] = byte;
 }
 
 static void
 memwrite16(uint16_t addr, uint16_t word)
 {
+        MEMORY_MIRROR(addr);
+
         /* bytes are stored in little-endian (low then high) */
         memory[addr] = word & 0xFF;
         memory[addr + 1] = (word & 0xFF00) >> 8;