diff options
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/boot/bootsect.s | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/arch/x86/boot/bootsect.s b/arch/x86/boot/bootsect.s new file mode 100644 index 0000000..ecbdf16 --- /dev/null +++ b/arch/x86/boot/bootsect.s @@ -0,0 +1,60 @@ +.code16 # Tell GAS to generate 16 bit code + +.global _start # Make the symbol visible to ld + +.include "bios.inc" + +.set MAGIC, 0xAA55 + +.section .text.bootentry # Code that will start executing at + # special address (specified in linker) +_start: + jmp $0x0, $_start2 # Normalize the start address + # CS = 0 and IP = _start2 +_start2: + mov %cs, %ax # AX = CS = 0 (see above) + mov %ax, %ds # Zero segment registers + mov %ax, %es + mov %ax, %ss # zero stack (?) + mov %ax, %sp # zero stack pointer (?) + # Don't touch FS and GS register (why?) + cld # Set direction flag for incrementing + mov %dl, boot_drive # BIOS stores our boot drive in DL, + # so we remember it + + BIOS_PRINT $boot_os_msg + + mov $0x02, %ah # Set BIOS read sector routine + mov boot_drive, %dl # Read drive number from $boot_drive + mov $0x00, %ch # Select cylinder 0 + mov $0x00, %dh # Select head 0 [has a base of 0] + mov $0x02, %cl # Select sector 2 (next after the + # boot sector) [has a base of 1] + mov $0x01, %al # Read 1 sectors + mov $0x9000, %bx # Load sectors to ES:BS (0x9000) + int $0x13 # Start reading from drive + jc disk_error # If carry flag set, bios failed to read + + # FIXME: we must compare different register + cmp %al, %al # If AL(sect. read) != <>(sect. expected) + jne disk_error # then return disk error + + jmp . # TODO: jump into the darkness + +disk_error: + BIOS_PRINT $disk_error_msg + jmp . + +# Global variables +boot_os_msg: + .asciz "Booting mfsos...\r\n" + +disk_error_msg: + .asciz "Disk read error!" + +boot_drive: + .byte 0 + +# Bootsector padding +.space 512 - 2 - (. - _start), 0 +.word MAGIC |