Add to README, finish makefile; project structure.

.gitignore

@@ -1,3 +1,5 @@
 build
 roms/*
 !roms/README
+crater
+crater-dev

README.md

@@ -1,6 +1,30 @@
 crater
+======
 
-**crater** is an emulator for the Sega Game Gear, written in C.
+**crater** is an emulator for the [Sega Game Gear](game gear), written in C.
 
-...
+[game gear]: https://en.wikipedia.org/wiki/Sega_Game_Gear
+
+Why?
+----
+
+While the internet is full of emulators for retro game systems, writing one is
+nevertheless a fun learning project.
+
+Crater is named after [31 Crateris](crateris), a star that was – for a short
+time in 1974 – misidentified as [a moon of Mercury](moon). Mercury was Sega's
+codename for the Game Gear during development.
+
+[crateris]: http://www.astrostudio.org/xhip.php?hip=58587
+[moon]: https://en.wikipedia.org/wiki/Mercury%27s_moon
+
+Installing
+----------
+
+Only OS X and Linux are tested. You'll need a decent compiler that supports C11
+(gcc, clang) and SDL 2. Using Homebrew, you can `brew install sdl2`; using apt,
+you can `apt-get install libsdl2-dev`.
+
+Run `make` and then `./crater`. To build the development version with debug
+symbols (they can exist simultaneously), run `make DEBUG=1` and then
+`./crater-dev`.

crater.c

@@ -0,0 +1,10 @@
+/* Copyright (C) 2014 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#include <stdio.h>
+#include <SDL.h>
+
+int main(int argc, char* argv[]) {
+    printf("Hello, world!\n");
+    return 0;
+}

makefile

@@ -0,0 +1,46 @@
+# Copyright (C) 2014 Ben Kurtovic <ben.kurtovic@gmail.com>
+# Released under the terms of the MIT License. See LICENSE for details.
+
+PROGRAM = crater
+SOURCES = src
+BUILD   = build
+DEVEXT  = -dev
+
+CC     = gcc
+FLAGS  = -O2 -Wall -pedantic -std=c11
+CFLAGS = $(shell sdl2-config --cflags)
+LIBS   = $(shell sdl2-config --libs)
+MKDIR  = mkdir -p
+RM     = rm -rf
+
+MODE = release
+SRCS = $(foreach d,.,$(wildcard *.c)) $(foreach d,$(SOURCES),$(wildcard $(addprefix $(d)/*,.c)))
+OBJS = $(patsubst %.c,%.o,$(addprefix $(BUILD)/$(MODE)/,$(SRCS)))
+DEPS = $(OBJS:%.o=%.d)
+DIRS = $(sort $(dir $(OBJS)))
+
+ifdef DEBUG
+	PROGRAM := $(PROGRAM)$(DEVEXT)
+	FLAGS   += -g
+	MODE     = debug
+endif
+
+.PHONY: all clean
+
+all: $(PROGRAM)
+
+clean:
+	$(RM) $(PROGRAM) $(PROGRAM)$(DEVEXT) $(BUILD)
+
+$(DIRS):
+	$(MKDIR) $@
+
+$(PROGRAM): $(OBJS)
+	$(CC) $(FLAGS) $(LIBS) $(OBJS) -o $@
+
+$(OBJS): | $(DIRS)
+
+$(BUILD)/$(MODE)/%.o: %.c
+	$(CC) $(FLAGS) $(CFLAGS) -MMD -MP -c $< -o $@
+
+-include $(DEPS)

src/z80.c

@@ -0,0 +1,4 @@
+/* Copyright (C) 2014 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#include "z80.h"

src/z80.h

@@ -0,0 +1,8 @@
+/* Copyright (C) 2014 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#pragma once
+
+struct register_t {
+    int pc;
+};