first mknes commit

1 files changed, 95 insertions, 0 deletions

diff --git a/memory.c b/memory.c
new file mode 100644
index 0000000..cb29344
--- /dev/null
+++ b/memory.c
@@ -0,0 +1,95 @@
+
+
+
+static uint8_t memory_read(struct nes_state *restrict state, uint32_t offset) {
+	state->cycle++;
+	for(uint32_t i = 0; i < 3; ++i) {
+		ppu_tick(state);
+	}
+
+	if(offset < 0x2000) {
+		return state->ram[offset & 0x07ff];
+	} else if(offset < 0x4000) {
+		switch(offset & 7) {
+			case 2: return ppu_read_2002(state);
+			case 4: return ppu_read_2004(state);
+			case 7: return ppu_read_2007(state);
+			default: return 0;
+		}
+	} else if(offset < 0x4020) {
+		// TODO: APU and I/O reads
+		return 0;
+	} else if(offset >= 0x6000) {
+		return state->mapper.read(state, offset);
+	} else {
+		return 0;
+	}
+}
+
+static void memory_write(struct nes_state *restrict state, uint32_t offset, uint8_t value) {
+	state->cycle++;
+	for(uint32_t i = 0; i < 3; ++i) {
+		ppu_tick(state);
+	}
+
+	if(offset < 0x2000) {
+		state->ram[offset & 0x07ff] = value;
+	} else if(offset < 0x4000) {
+		switch(offset & 7) {
+			case 0: state->ppu.ctrl = value; break;
+			case 1: state->ppu.mask = value; break;
+			case 3: ppu_write_2003(state, value); break;
+			case 4: ppu_write_2004(state, value); break;
+			case 5: ppu_write_2005(state, value); break;
+			case 6: ppu_write_2006(state, value); break;
+			case 7: ppu_write_2007(state, value); break;
+			default: break;
+		}
+	} else if(offset == 0x4014) {
+		ppu_dma_4014(state, value);
+	} else if(offset < 0x4020) {
+		// TODO: APU and I/O writes
+	} else if(offset >= 0x6000) {
+		state->mapper.write(state, offset, value);
+	}
+}
+
+static uint8_t memory_read_dma(struct nes_state *restrict state, uint32_t offset) {
+	// Do not tick CPU/PPU/APU — caller handles timing
+	if(offset < 0x2000) {
+		return state->ram[offset & 0x07ff];
+	} else if(offset < 0x4000) {
+		// PPU register reads are ignored during DMA
+		return 0;
+	} else if(offset < 0x4020) {
+		// APU and I/O — usually ignored or blocked during DMA
+		return 0;
+	} else if(offset >= 0x6000) {
+		return state->mapper.read(state, offset);
+	} else {
+		return 0;
+	}
+}
+
+static uint8_t memory_read_dummy(struct nes_state *restrict state, uint32_t offset) {
+	state->cycle++;
+	for(uint32_t i = 0; i < 3; ++i) {
+		ppu_tick(state);
+	}
+
+	if(offset < 0x2000) {
+		return 0;
+	} else if(offset < 0x4000) {
+		switch(offset & 7) {
+			case 2: return ppu_read_2002(state);
+			case 7: return ppu_read_2007(state);
+			default: return 0;
+		}
+	} else if(offset < 0x4020) {
+		return 0;
+	} else if(offset >= 0x6000) {
+		return state->mapper.read(state, offset);
+	} else {
+		return 0;
+	}
+}