commit 3e264da356ccbd3878d552f6de1006448ae9a1b9
Author: Matt Laux <matthew.laux@gmail.com>
Date:   Tue Apr 16 01:25:00 2019 -0500

    initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1377554
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.swp
diff --git a/src/cpu.c b/src/cpu.c
new file mode 100644
index 0000000..21b682a
--- /dev/null
+++ b/src/cpu.c
@@ -0,0 +1,80 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "cpu.h"
+#include "types.h"
+
+void cpu_bind_mem_model(
+    struct cpu *cpu,
+    void *mem_model,
+    u8 (*mem_read)(void *, u16),
+    void (*mem_write)(void *, u16, u8)
+) {
+    cpu->mem_model = mem_model;
+    cpu->mem_read = mem_read;
+    cpu->mem_write = mem_write;
+}
+
+static inline u16 read_af(struct cpu *cpu)
+{
+    return cpu->a << 8 | cpu->f;
+}
+
+static inline u16 read_bc(struct cpu *cpu)
+{
+    return cpu->b << 8 | cpu->c;
+}
+
+static inline u16 read_de(struct cpu *cpu)
+{
+    return cpu->d << 8 | cpu->e;
+}
+
+static inline u16 read_hl(struct cpu *cpu)
+{
+    return cpu->h << 8 | cpu->l;
+}
+
+static inline void write_af(struct cpu *cpu, int value)
+{
+    cpu->a = value >> 8;
+    cpu->f = value & 0xff;
+}
+
+static inline void write_bc(struct cpu *cpu, int value)
+{
+    cpu->b = value >> 8;
+    cpu->c = value & 0xff;
+}
+
+static inline void write_de(struct cpu *cpu, int value)
+{
+    cpu->d = value >> 8;
+    cpu->e = value & 0xff;
+}
+
+static inline void write_hl(struct cpu *cpu, int value)
+{
+    cpu->h = value >> 8;
+    cpu->l = value & 0xff;
+}
+
+void cpu_panic(struct cpu *cpu)
+{
+    printf("a=%02x f=%02x b=%02x c=%02x\n", cpu->a, cpu->f, cpu->b, cpu->c);
+    printf("d=%02x e=%02x h=%02x l=%02x\n", cpu->d, cpu->e, cpu->h, cpu->l);
+    exit(0);
+}
+
+void cpu_step(struct cpu *cpu)
+{
+    u8 opc = cpu->mem_read(cpu->mem_model, cpu->pc);
+    switch (opc) {
+        case 0: // NOP
+            cpu->pc++;
+            break;
+        default:
+            printf("unknown opcode %02x\n", opc);
+            cpu_panic(cpu);
+    }
+}
diff --git a/src/cpu.h b/src/cpu.h
new file mode 100644
index 0000000..a565d73
--- /dev/null
+++ b/src/cpu.h
@@ -0,0 +1,38 @@
+#ifndef _CPU_H
+#define _CPU_H
+
+#include "types.h"
+
+struct cpu
+{
+    u8 a;
+    u8 f;
+    u8 b;
+    u8 c;
+    u8 d;
+    u8 e;
+    u8 h;
+    u8 l;
+    u16 sp;
+    u16 pc;
+
+    u8 (*mem_read)(void *, u16);
+    void (*mem_write)(void *, u16, u8);
+    void *mem_model;
+};
+
+void cpu_bind_mem_model(
+    struct cpu *cpu,
+    void *mem_model,
+    u8 (*mem_read)(void *, u16),
+    void (*mem_write)(void *, u16, u8)
+);
+
+void cpu_step(struct cpu *cpu);
+
+#define FLAG_Z(cpu) ((cpu)->f >> 7 & 1)
+#define FLAG_N(cpu) ((cpu)->f >> 6 & 1)
+#define FLAG_H(cpu) ((cpu)->f >> 5 & 1)
+#define FLAG_C(cpu) ((cpu)->f >> 4 & 1)
+
+#endif
diff --git a/src/dmg.c b/src/dmg.c
new file mode 100644
index 0000000..c3c9bb6
--- /dev/null
+++ b/src/dmg.c
@@ -0,0 +1,36 @@
+#include "cpu.h"
+#include "rom.h"
+#include "dmg.h"
+#include "types.h"
+
+void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom)
+{
+    dmg->cpu = cpu;
+    dmg->rom = rom;
+}
+
+u8 dmg_read(void *_dmg, u16 address)
+{
+    struct dmg *dmg = (struct dmg *) _dmg;
+    if (address < 0x4000) {
+        return dmg->rom->data[address];
+    } else if (address < 0x8000) {
+        // TODO switchable rom bank
+        return dmg->rom->data[address];
+    } else if (address < 0xa000) {
+        return dmg->video_ram[address - 0x8000];
+    } else if (address < 0xc000) {
+        // TODO switchable ram bank
+        return 0;
+    } else if (address < 0xe000) {
+        return dmg->main_ram[address - 0xc000];
+    } else {
+        // not sure about any of this yet
+        return 0;
+    }
+}
+
+void dmg_write(void *_dmg, u16 address, u8 data)
+{
+    struct dmg *dmg = (struct dmg *) _dmg;
+}
diff --git a/src/dmg.h b/src/dmg.h
new file mode 100644
index 0000000..2070a48
--- /dev/null
+++ b/src/dmg.h
@@ -0,0 +1,19 @@
+#ifndef _DMG_H
+#define _DMG_H
+
+#include "cpu.h"
+#include "rom.h"
+
+struct dmg {
+    struct cpu *cpu;
+    struct rom *rom;
+    u8 main_ram[0x2000];
+    u8 video_ram[0x2000];
+};
+
+void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom);
+
+u8 dmg_read(void *dmg, u16 address);
+void dmg_write(void *dmg, u16 address, u8 data);
+
+#endif
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..997bb6a
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,37 @@
+#include <stdio.h>
+
+#include "dmg.h"
+#include "cpu.h"
+#include "rom.h"
+
+int main(int argc, char *argv[])
+{
+    struct cpu cpu;
+    struct rom rom;
+    struct dmg dmg;
+
+    if (argc < 2) {
+        printf("no rom specified\n");
+        return 1;
+    }
+
+    if (!rom_load(&rom, argv[1])) {
+        printf("error loading rom\n");
+        return 1;
+    }   
+
+    // this might be too much abstraction but it'll let me
+    // test the cpu, rom, and dmg independently and use the cpu
+    // for other non-GB stuff
+    dmg_new(&dmg, &cpu, &rom);
+    cpu_bind_mem_model(&cpu, &dmg, dmg_read, dmg_write);
+
+    cpu.pc = 0x100;
+
+    while (1) {
+        cpu_step(&cpu);
+    }
+
+    rom_free(&rom);
+    return 0;
+}
diff --git a/src/rom.c b/src/rom.c
new file mode 100644
index 0000000..7eaa1e2
--- /dev/null
+++ b/src/rom.c
@@ -0,0 +1,32 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "rom.h"
+#include "types.h"
+
+int rom_load(struct rom *rom, const char *filename)
+{
+    FILE *fp;
+    int len;
+
+    fp = fopen(filename, "r");
+    if (!fp) {
+        return 0;
+    }
+
+    fseek(fp, 0, SEEK_END);
+    len = ftell(fp);
+    rewind(fp);
+
+    rom->type = 0; // TODO read type from cart
+    rom->data = malloc(len);
+    if (fread(rom->data, 1, len, fp) < len) {
+        return 0;
+    }
+
+    return 1;
+}
+
+void rom_free(struct rom *rom)
+{
+    free(rom->data);
+}
diff --git a/src/rom.h b/src/rom.h
new file mode 100644
index 0000000..97e1cfc
--- /dev/null
+++ b/src/rom.h
@@ -0,0 +1,16 @@
+#ifndef _ROM_H
+#define _ROM_H
+
+#include "types.h"
+
+struct rom {
+    int type;
+    u8 *data;
+};
+
+
+int rom_load(struct rom *rom, const char *filename);
+
+void rom_free(struct rom *rom);
+
+#endif
diff --git a/src/types.h b/src/types.h
new file mode 100644
index 0000000..0404438
--- /dev/null
+++ b/src/types.h
@@ -0,0 +1,7 @@
+#ifndef _TYPES_H
+#define _TYPES_H
+
+typedef unsigned char u8;
+typedef unsigned short u16;
+
+#endif