From 7d148924e2fee1a2692d2c49a01e6770b630f906 Mon Sep 17 00:00:00 2001
From: vin <git@vineetk.net>
Date: Sun, 21 Jul 2024 13:53:04 -0400
Subject: [PATCH] start implementing PPU

---
 cpu.c | 27 +++++++++++++++++++++------
 ppu.c | 15 +++++++++++++++
 ppu.h | 23 +++++++++++++++++++++++
 rom.h |  5 +++++
 4 files changed, 64 insertions(+), 6 deletions(-)
 create mode 100644 ppu.c
 create mode 100644 ppu.h

diff --git a/cpu.c b/cpu.c
index 8df2bf9..621fe5b 100644
--- a/cpu.c
+++ b/cpu.c
@@ -8,6 +8,7 @@
 #include "cpu.h"
 #include "opcodes.h"
 #include "rom.h"
+#include "ppu.h"
 
 #define MAX(a, b)	((a > b) ? a : b)
 
@@ -145,15 +146,24 @@ opcode_mem(enum addressing_mode mode)
 	return val;
 }
 
+static void
+tick(void)
+{
+	cycles++;
+	ppu_tick();
+	ppu_tick();
+	ppu_tick();
+}
+
 static void
 branch(uint16_t addr, bool cond)
 {
 	if (!cond)
 		return;
-	cycles++;
+	tick();
 
 	if (((regs.pc + 1) & 0xFF00) != (addr & 0xFF00))
-		cycles++;
+		tick();
 
 	regs.pc = addr;
 }
@@ -946,18 +956,21 @@ interpret(void)
 
 		while (spaces--) putchar(' ');
 
-		printf("A:%02X X:%02X Y:%02X P:%02X SP:%02X CYC:%d\n",
-		    regs.a, regs.x, regs.y, STATUS_TO_INT(), regs.sp, cycles);
+		printf("A:%02X X:%02X Y:%02X P:%02X SP:%02X PPU:%3d,%3d CYC:%d\n",
+		    regs.a, regs.x, regs.y, STATUS_TO_INT(), regs.sp,
+		    ppu.scanlines, ppu.cycles, cycles);
 
 		if (opcodes[op].memread)
 			opcodes[op].instr(peek(arg));
 		else
 			opcodes[op].instr(arg);
 
-		cycles += opcodes[op].cycles;
+		for (uint8_t i = 0; i < opcodes[op].cycles; i++)
+			tick();
+
 		if (page_crossed) {
 			if (opcodes[op].page_cross)
-				cycles++;
+				tick();
 			page_crossed = false;
 		}
 	}
@@ -976,6 +989,8 @@ cpu_init(void)
 	regs.status.unused = 1;
 
 	cycles += 7;
+	for (uint8_t i = 0; i < 7 * 3; i++)
+		ppu_tick();
 }
 
 int
diff --git a/ppu.c b/ppu.c
new file mode 100644
index 0000000..4ae0162
--- /dev/null
+++ b/ppu.c
@@ -0,0 +1,15 @@
+#include "ppu.h"
+
+struct ppu ppu = {0};
+
+void
+ppu_tick(void)
+{
+	ppu.cycles++;
+	if (ppu.cycles >= 341) {
+		ppu.cycles -= 341;
+		ppu.scanlines++;
+	}
+	if (ppu.scanlines >= 262)
+		ppu.scanlines -= 262;
+}
diff --git a/ppu.h b/ppu.h
new file mode 100644
index 0000000..1527b93
--- /dev/null
+++ b/ppu.h
@@ -0,0 +1,23 @@
+#ifndef PPU_H
+#define PPU_H
+
+#include <stdio.h>
+#include <stdint.h>
+
+#include "rom.h"
+
+struct ppu {
+	uint8_t oam[64*4];
+	uint8_t vram[2048];
+	uint8_t palette[16*2];
+	uint16_t cycles, scanlines;
+	/* copied from rom */
+	uint8_t *chr_rom;
+	size_t chr_rom_size;
+	enum screen_mirroring mirror;
+};
+extern struct ppu ppu;
+
+void ppu_tick(void);
+
+#endif /* PPU_H */
diff --git a/rom.h b/rom.h
index a52bda1..703fabd 100644
--- a/rom.h
+++ b/rom.h
@@ -1,3 +1,6 @@
+#ifndef ROM_H
+#define ROM_H
+
 enum screen_mirroring {
 	M_HORIZONTAL,
 	M_VERTICAL,
@@ -15,3 +18,5 @@ struct Rom {
 
 void parse_rom(const uint8_t *data, size_t data_len, struct Rom *rom);
 void free_rom(struct Rom *rom);
+
+#endif /* ROM_H */