From 32336b183a5d3cbf64d2c67100afe036cf610694 Mon Sep 17 00:00:00 2001
From: Daniel Jones <admin@danieljon.es>
Date: Sun, 16 Aug 2020 23:05:55 +0930
Subject: began chip8 interpreter, reading rom file

---
 CMakeLists.txt |  2 +-
 chip8.c        | 41 +++++++++++++++++++++++++++++++++++++++++
 chip8.h        | 19 +++++++++++++++++++
 main.c         | 31 ++++++++++++++++++++++++++-----
 4 files changed, 87 insertions(+), 6 deletions(-)
 create mode 100644 chip8.c
 create mode 100644 chip8.h

diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd54795..bda00bc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,7 +8,7 @@ find_package(SDL2 REQUIRED)
 
 add_executable(
 	chip8
-	main.c)
+	main.c chip8.c chip8.h)
 
 target_compile_options(chip8 PRIVATE -Wall)
 
diff --git a/chip8.c b/chip8.c
new file mode 100644
index 0000000..3c41117
--- /dev/null
+++ b/chip8.c
@@ -0,0 +1,41 @@
+#include "chip8.h"
+
+uint8_t key[KEY_SIZE]; 		// hex key input
+uint32_t video[WIDTH*HEIGHT]; 	// video memory TODO: video should be 8 bit not 32
+uint8_t V[16];			// registers - 0x0 to 0xF
+uint16_t I;			// special I register, stores addresses
+uint16_t PC;			// program counter
+uint8_t SP;			// stack pointer
+uint16_t stack[STACK_SIZE];	// stack, for address storage when using subroutines, maximum of 16 levels of nested subroutines
+uint8_t memory[MEMORY_SIZE];	// 4KB of program memory
+
+int
+load_rom(char *rom)
+{
+	int ret = 1;
+	printf("loading rom %s..\n", rom);
+	FILE *romfile;
+	romfile = fopen(rom, "rb");
+	if (romfile == NULL)
+	{
+		fprintf(stderr, "cannot read rom %s: %s\n", rom, strerror(errno));
+		ret = 0;
+	}
+
+	/* read a maximum of MAX_ROM_SIZE bytes into memory starting after the reserved memory */
+	fread(&memory[0x200], 1, MAX_ROM_SIZE, romfile);
+
+	fclose(romfile);
+	return ret;
+}
+
+void
+chip8_init()
+{
+	/* clear everything */
+	memset(key, 0, 15);
+	memset(video, 0, (WIDTH*HEIGHT) * sizeof(uint32_t));
+	memset(V, 0, 16);
+	memset(stack, 0, (STACK_SIZE) * sizeof(uint16_t));
+	memset(memory, 0, MEMORY_SIZE);
+}
diff --git a/chip8.h b/chip8.h
new file mode 100644
index 0000000..7301c45
--- /dev/null
+++ b/chip8.h
@@ -0,0 +1,19 @@
+#ifndef CHIP8_H
+#define CHIP8_H
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+
+#define WIDTH 64
+#define HEIGHT 32
+#define KEY_SIZE 15
+#define MEMORY_SIZE 4096
+#define STACK_SIZE 16
+#define MAX_ROM_SIZE 0x1000 - 0x200 // memory size - reseved memory
+
+int load_rom();
+void chip8_init();
+
+#endif
diff --git a/main.c b/main.c
index 056e5b1..a3b9539 100644
--- a/main.c
+++ b/main.c
@@ -1,8 +1,8 @@
 #include <stdio.h>
+#include <stdlib.h>
 #include <SDL2/SDL.h>
 
-#define WIDTH 64
-#define HEIGHT 32
+#include "chip8.h"
 
 /* references
  * https://austinmorlan.com/posts/chip8_emulator/
@@ -21,6 +21,15 @@ void init_video();
 void update_video();
 void toggle_pixel(int x, int y);
 void quit();
+void usage(char *);
+
+extern uint32_t video[WIDTH*HEIGHT];
+
+void
+usage(char *program)
+{
+	printf("usage: %s [romfile]\n", program);
+}
 
 void
 quit()
@@ -41,8 +50,6 @@ init_video()
 	texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
 }
 
-uint32_t video[WIDTH*HEIGHT];
-
 void
 update_video()
 {
@@ -79,6 +86,20 @@ toggle_pixel(int x, int y)
 
 int main(int argc, char *argv[])
 {
+	if (argc < 2)
+	{
+		usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	if (!load_rom(argv[1]))
+	{
+		fprintf(stderr, "cannot start interpreter\n");
+		exit(EXIT_FAILURE);
+	}
+
+	chip8_init();
+
 	init_video();
 
 	const int fps = 60;
@@ -101,5 +122,5 @@ int main(int argc, char *argv[])
 	}
 
 	quit();
-	return 0;
+	return EXIT_SUCCESS;
 }
-- 
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