beginning ppu

lib/dma.c

@@ -0,0 +1,40 @@
+#include <dma.h>
+#include <ppu.h>
+#include <bus.h>
+
+typedef struct {
+    bool active;
+    u8 byte;
+    u8 value;
+    u8 start_delay;
+} dma_context;
+
+static dma_context ctx;
+
+void dma_start(u8 start) {
+    ctx.active = true;
+    ctx.byte = 0;
+    ctx.start_delay = 2;
+    ctx.value = start;
+}
+
+void dma_tick() {
+    if (!ctx.active) {
+        return;
+    }
+
+    if (ctx.start_delay) {
+        ctx.start_delay--;
+        return;
+    }
+
+    ppu_oam_write(ctx.byte, bus_read((ctx.value * 0x100) + ctx.byte));
+
+    ctx.byte++;
+
+    ctx.active = ctx.byte < 0xA0;
+}
+
+bool dma_transferring() {
+    return ctx.active;
+}