Add screen(), memory mapped frame buffer
diff --git a/cpu.h b/cpu.h
index 4629b14..cee84c5 100644
--- a/cpu.h
+++ b/cpu.h
@@ -4,6 +4,9 @@
 #include <stdbool.h>
 
 #define REGISTERS R(A) R(X) R(Y) R(SP)
+#define CPU_FB_ADDR 0x200
+#define CPU_FB_W 32
+#define CPU_FB_H 32
 
 enum // Registers
 {