X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot.s;h=4f0023a025b4c97d55cfda9e04914fe83e1c5f90;hp=e3fd206ba416396c23b0df24bb4e83772437d19c;hb=e253f9a0cad14f636a51f6211308491ab19dfbe5;hpb=e5b5905eb3134a409638a5a20462000ef159e1e6 diff --git a/src/boot/boot.s b/src/boot/boot.s index e3fd206..4f0023a 100644 --- a/src/boot/boot.s +++ b/src/boot/boot.s @@ -1,37 +1,288 @@ +# pcboot - bootable PC demo/game kernel +# Copyright (C) 2018-2019 John Tsiombikas +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY, without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . + .code16 - .section .boot,"a" - - mov $0x13, %ax - int $0x10 - - mov $1, %al - mov $0x3c8, %dx - outb %al, %dx - mov $0x3c9, %dx - mov $63, %al - outb %al, %dx - xor %al, %al - outb %al, %dx - outb %al, %dx - - mov $200, %ebx - mov $0x00000101, %eax - pushl $0xa000 - popl %es - xor %di, %di -fill: - mov %ebx, %ecx - and $1, %ecx - jnz 0f - rol $16, %eax -0: mov $80, %ecx - rep stosl - dec %ebx - jnz fill + .section .boot,"ax" + + .set stack_top, 0x7be0 + .set read_retries, 0x7be8 + .set drive_number, 0x7bec + .set cursor_x, 0x7bee + .set scratchbuf, 0x7bf0 + .set scratchbuf_size, 16 +boot: cli + # move stack to just below the code + xor %ax, %ax + mov %ax, %ss + mov $stack_top, %sp + # use the code segment for data access + mov %cs, %ax + mov %ax, %ds + mov %ax, %es + + mov %dl, drive_number + + call get_drive_chs + + mov $loading_msg, %si + call print_str + + # load the second stage boot loader and jump to it + mov $_boot2_size, %eax + call print_num + + mov $_boot2_size, %eax + mov %eax, %ebx + shr $9, %eax + and $0x1ff, %ebx + jz 0f + inc %ax +0: pushw %ax + pushw $1 + # set es to the start of the destination buffer to allow reading in + # full 64k chunks + mov $boot2_addr, %bx + shr $4, %bx + mov %bx, %es + xor %bx, %bx + call read_sectors + jmp boot2_addr + +loading_msg: .asciz "\nLoad " +driveno_msg: .asciz "Drv:" + + .global sect_per_track +sect_per_track: .short 18 + .global num_cylinders +num_cylinders: .short 80 + .global num_heads +num_heads: .short 2 + .global heads_mask +heads_mask: .byte 1 + +get_drive_chs: + mov $driveno_msg, %si + call print_str + xor %eax, %eax + movb drive_number, %dl + mov %dl, %al + call print_num + mov $10, %al + call print_char + + mov $8, %ah + int $0x13 + jnc ok + ret + +ok: xor %eax, %eax + mov %ch, %al + mov %cl, %ah + rol $2, %ah + inc %ax + and $0x3ff, %ax + mov %ax, num_cylinders + + and $0x3f, %cx + mov %cx, sect_per_track + + shr $8, %dx + mov %dl, heads_mask + inc %dx + mov %dx, num_heads + + call print_num + mov $47, %al + call print_char + mov %dx, %ax + call print_num + mov $47, %al + call print_char + mov %cx, %ax + call print_num + ret + + + .set ARG_NSECT, 6 + .set ARG_SIDX, 4 + +# read_sectors(first, num) +read_sectors: + push %bp + mov %sp, %bp + + mov ARG_SIDX(%bp), %ax + xor %cx, %cx + + jmp 1f +0: push %ax + call read_sector + pop %ax + inc %ax + inc %cx +1: cmp ARG_NSECT(%bp), %cx + jnz 0b + + pop %bp + ret + +# read_sector(sidx) +read_sector: + push %bp + mov %sp, %bp + push %cx + push %dx + + movw $3, read_retries + +read_try: + # calculate the track (sidx / sectors_per_track) + mov 4(%bp), %ax + + xor %dx, %dx + mov sect_per_track, %cx + div %cx + mov %ax, %cx + # save the remainder + push %dx + # head in dh + mov %cl, %dh + and heads_mask, %dh + # cylinder (track/heads) in ch [0-7] and cl[6,7]<-[8,9] + push %dx + xor %dx, %dx + movw num_heads, %cx + div %cx + pop %dx + mov %ax, %cx + rol $8, %cx + ror $2, %cl + and $0xc0, %cl + # sector num cl[0-5] is sidx % sectors_per_track + 1 + pop %ax + inc %al + or %al, %cl + + # ah = 2 (read), al = 1 sectors + mov $0x0201, %ax + movb drive_number, %dl + int $0x13 + jnc read_ok + + # abort after 3 attempts + decw read_retries + jz read_fail + + # error detected, reset controller and retry + xor %ah, %ah + int $0x13 + jmp read_try + +read_fail: + mov 4(%bp), %ax + jmp abort_read + +read_ok: + mov $46, %ax + call print_char + + # increment es:bx accordingly (advance es if bx overflows) + add $512, %bx + jnc 0f + mov %es, %ax + add $4096, %ax + mov %ax, %es + +0: pop %dx + pop %cx + pop %bp + ret + +str_read_error: .asciz "rderr:" + +abort_read: + mov $str_read_error, %si + call print_str + and $0xffff, %eax + call print_num + mov $10, %al + call print_char hlt + # expects string pointer in ds:si +print_str: + pusha + +0: mov (%si), %al + cmp $0, %al + jz end + call print_char + inc %si + jmp 0b + +end: popa + ret + + # expects character in al +print_char: + push %es + + cmp $10, %ax + jnz 0f + mov $32, %ax + +0: pushw $0xb800 + pop %es + movw cursor_x, %di + shl $1, %di + + mov %al, %es:(%di) + movb $7, %es:1(%di) + incw cursor_x + + pop %es + ret + + # expects number in eax + .global print_num +print_num: + # save registers + pusha + + movw $scratchbuf + scratchbuf_size, %si + movb $0, (%si) + mov $10, %ebx +convloop: + xor %edx, %edx + div %ebx + add $48, %dl + dec %si + mov %dl, (%si) + cmp $0, %eax + jnz convloop + + call print_str + + # restore regs + popa + ret + .org 510 .byte 0x55 .byte 0xaa +boot2_addr: