add basic ppu register reading

1 files changed, 12 insertions, 3 deletions

diff --git a/ppu.h b/ppu.h
index ffd66d7..c5483e1 100644
--- a/ppu.h
+++ b/ppu.h
@@ -7,12 +7,23 @@
 #include "rom.h"
 
 struct ppu {
-	uint8_t oam[64*4];
 	uint8_t vram[2048];
+	uint8_t oam[64*4];
+	uint8_t oam_addr;	/* $2003 */
 	uint8_t palette[16*2];
 	uint16_t cycles, scanlines;
 	struct rom *rom;
 
+	uint8_t last_read;
+
+	struct ppu_regs {
+		uint16_t v : 15; /* current vram address */
+		uint16_t t : 15; /* temporary vram address */
+		uint8_t x : 3;   /* fine x scroll */
+		uint8_t w : 1;   /* first/second write toggle */
+		uint8_t padding : 6;
+	} regs;
+
 	struct ppu_ctrl {	/* $2000 */
 		uint8_t nmi_enable : 1;
 		uint8_t master_slave : 1;
@@ -36,8 +47,6 @@ struct ppu {
 		uint8_t sprite_overflow : 1;
 		uint8_t pad : 5;
 	} status;
-	uint8_t oam_addr;	/* $2003 */
-	uint8_t oam_data;	/* $2004 */
 };
 extern struct ppu ppu;