Set display mode and busy-loop VSync

src/main.cpp

@@ -1,3 +1,18 @@
+#include <tonc.h>
+
 int main(void) {
+	// Mode 3-5 are bitmap modes.
+	// 	3: 240x160 @ 16bpp N page-flip
+	// 	4: 240x160 @ 8bpp  Y page-flip
+	// 	5: 160x128 @ 16bpp Y page-flip
+	//
+	// BG2 is the only available background in bitmap modes.
+	REG_DISPCNT = DCNT_MODE3 | DCNT_BG2;
+
+	while (true) {
+		// Busy-loop VSync, should be replaced with an interrupt.
+		vid_vsync();
+	}
+
 	return 0;
 }