From 7fa1ecc4e44a33879028e252e15482a32d3678ea Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Sat, 22 Feb 2020 23:17:52 +0000
Subject: let's get started.

---
 gbafix.c | 124 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 readme   |   3 ++
 2 files changed, 127 insertions(+)
 create mode 100644 gbafix.c
 create mode 100644 readme

diff --git a/gbafix.c b/gbafix.c
new file mode 100644
index 0000000..e1eb83d
--- /dev/null
+++ b/gbafix.c
@@ -0,0 +1,124 @@
+#include <u.h>
+#include <libc.h>
+
+enum {
+	AROM		= 0x00,
+	ALOGO		= 0x04,
+	ATITLE		= 0xA0,
+	AGAME		= 0xAC,
+	AMAKER		= 0xB0,
+	AFIXED		= 0xB2,
+	AUNIT		= 0xB3,
+	ADEVTYPE	= 0xB4,
+	ARES0		= 0xB5,
+	AVERSION	= 0xBC,
+	ACKSUM		= 0xBD,
+	ARES1		= 0xBE,
+	AEND		= 0xC0
+};
+
+typedef struct Header Header;
+
+struct Header
+{
+	u32int	start;		/* ARM entry point branch opcode */
+	u8int	logo[156];	/* the Nintendo logo */
+	u8int	title[12];
+	u32int	game;
+	u16int	maker;
+	u8int	fixed;		/* 0x96 */
+	u8int	unit;
+	u8int	devtype;
+	u8int	r0[7];		/* reserved area */
+	u8int	version;
+	u8int	cksum;
+	u8int	r1[2];		/* reserved area */
+};
+
+u8int nintendō[156] = {
+	0x24,0xFF,0xAE,0x51,0x69,0x9A,0xA2,0x21,0x3D,0x84,0x82,0x0A,0x84,0xE4,0x09,0xAD,
+	0x11,0x24,0x8B,0x98,0xC0,0x81,0x7F,0x21,0xA3,0x52,0xBE,0x19,0x93,0x09,0xCE,0x20,
+	0x10,0x46,0x4A,0x4A,0xF8,0x27,0x31,0xEC,0x58,0xC7,0xE8,0x33,0x82,0xE3,0xCE,0xBF,
+	0x85,0xF4,0xDF,0x94,0xCE,0x4B,0x09,0xC1,0x94,0x56,0x8A,0xC0,0x13,0x72,0xA7,0xFC,
+	0x9F,0x84,0x4D,0x73,0xA3,0xCA,0x9A,0x61,0x58,0x97,0xA3,0x27,0xFC,0x03,0x98,0x76,
+	0x23,0x1D,0xC7,0x61,0x03,0x04,0xAE,0x56,0xBF,0x38,0x84,0x00,0x40,0xA7,0x0E,0xFD,
+	0xFF,0x52,0xFE,0x03,0x6F,0x95,0x30,0xF1,0x97,0xFB,0xC0,0x85,0x60,0xD6,0x80,0x25,
+	0xA9,0x63,0xBE,0x03,0x01,0x4E,0x38,0xE2,0xF9,0xA2,0x34,0xFF,0xBB,0x3E,0x03,0x44,
+	0x78,0x00,0x90,0xCB,0x88,0x11,0x3A,0x94,0x65,0xC0,0x7C,0x63,0x87,0xF0,0x3C,0xAF,
+	0xD6,0x25,0xE4,0x8B,0x38,0x0A,0xAC,0x72,0x21,0xD4,0xF8,0x07
+};
+
+char
+cksum(Header *h)
+{
+	int n;
+	char c, *p;
+
+	c = 0;
+	p = (char*)h;
+	p += ATITLE;
+	for(n = 0; n < ACKSUM-ATITLE; n++)
+		c += *p++;
+	return -(0x19+c);
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s [-t title] [-g gamecode] [-m makercode] [-v version] rom\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Header h;
+	char *title;
+	u32int gcode;
+	u16int mcode;
+	u8int vcode;
+	int fd;
+
+	title = nil;
+	gcode = mcode = vcode = 0;
+	ARGBEGIN{
+	case 't':
+		title = EARGF(usage());
+		break;
+	case 'g':
+		gcode = strtoul(EARGF(usage()), nil, 0);
+		break;
+	case 'm':
+		mcode = strtoul(EARGF(usage()), nil, 0);
+		break;
+	case 'v':
+		vcode = strtoul(EARGF(usage()), nil, 0);
+		break;
+	default: usage();
+	}ARGEND;
+	if(argc != 1)
+		usage();
+	fd = open(argv[0], ORDWR);
+	if(fd < 0)
+		sysfatal("open: %r");
+	memset(&h, 0, sizeof h);
+	if(readn(fd, &h, sizeof(Header)) != sizeof(Header))
+		sysfatal("readn: %r");
+	memmove(h.logo, nintendō, sizeof(nintendō));
+	if(title)
+		memmove(h.title, title, strlen(title) < sizeof(h.title)? strlen(title): sizeof(h.title));
+	if(gcode)
+		h.game = gcode;
+	if(mcode)
+		h.maker = mcode;
+	h.fixed = 0x96;
+	h.devtype = 0x00;
+	if(vcode)
+		h.version = vcode;
+	h.cksum = cksum(&h);
+	seek(fd, 0, 0);
+	if(write(fd, &h, sizeof(Header)) != sizeof(Header))
+		sysfatal("write: %r");
+	close(fd);
+	exits(0);
+}
diff --git a/readme b/readme
new file mode 100644
index 0000000..5e00a50
--- /dev/null
+++ b/readme
@@ -0,0 +1,3 @@
+Tools for GBA ROM development
+
+so far i've got gbafix(1). more should come later.
-- 
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