add readme

README.md

@@ -1,2 +1,35 @@
-### MBR bootloader
+# FAT16 bootloader
+	x86 FAT16 bootloader
+	
+### How to run
+	1. install image to device
+		install to device
+			./install.sh /dev/sda
+		create image and install
+			./install.sh
+	2. run with qemu
+		qemu-systme-i386 [device | ./build/img]
 
+### Disk layout
+	0x0000 ~ 0x0200: "mbr"
+	0x8000 ~ *     : Using FAT16 filesystem
+	0x8000 ~ 0x8200: "biosboot"
+	    exist "boot" somewhere in FAT16 
+
+### How to work
+	mbr
+		1. bios take us to 0x7C00
+		2. relocate 0x7c00~0x7DFF to 0x7A00~0x7BFF
+		3. load "biosboot" to 0x7C00~0x7DFF
+		4. jump to 0x7c00 => biosboot
+	biosboot
+		1. find "boot" file in FAT16 file sysytem
+		2. load "boot" to 0x40000
+		2-1. 0x40000 ~ 0x401ff: ELF information
+			 0x40120 ~ *      : text, data, bss section 
+		3. jump to 0x40120 => boot
+	boot
+		1. set Global Descriptor Table
+		2. enter protected mode
+		2. set Interrupt Descriptor Table
+		3. call boot function 

boot/boot.c

@@ -60,7 +60,6 @@ wr8(u8 c, u8 fg, u8 bg, int x, int y)
      *where = c | (attrib << 8);
 }
 
-
 void
 boot(dev_t bootdev)
 {