X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot.s;h=4f0023a025b4c97d55cfda9e04914fe83e1c5f90;hp=ac4a424c5ce713814642489e4ccd10152c7cc682;hb=e253f9a0cad14f636a51f6211308491ab19dfbe5;hpb=07db0aabb3ad8dbb0a3cee2d3837dd93792ae825 diff --git a/src/boot/boot.s b/src/boot/boot.s index ac4a424..4f0023a 100644 --- a/src/boot/boot.s +++ b/src/boot/boot.s @@ -1,12 +1,35 @@ +# 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" + .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 - cld # move stack to just below the code xor %ax, %ax mov %ax, %ss - mov $0x7c00, %sp + mov $stack_top, %sp # use the code segment for data access mov %cs, %ax mov %ax, %ds @@ -14,12 +37,15 @@ mov %dl, drive_number - call clearscr + 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 - # load the second stage boot loader and jump to it mov $_boot2_size, %eax mov %eax, %ebx shr $9, %eax @@ -37,10 +63,60 @@ call read_sectors jmp boot2_addr - cli - hlt +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 SECT_PER_TRACK, 18 .set ARG_NSECT, 6 .set ARG_SIDX, 4 @@ -65,161 +141,148 @@ read_sectors: pop %bp ret - .set VAR_ATTEMPTS, -2 - # read_sector(sidx) read_sector: push %bp mov %sp, %bp - sub $2, %sp push %cx push %dx - movw $3, VAR_ATTEMPTS(%bp) + movw $3, read_retries -.Lread_try: +read_try: # calculate the track (sidx / sectors_per_track) mov 4(%bp), %ax + xor %dx, %dx - mov $SECT_PER_TRACK, %cx + mov sect_per_track, %cx div %cx mov %ax, %cx - # save the remainder in ax - mov %dx, %ax + # save the remainder + push %dx # head in dh mov %cl, %dh - and $1, %dh - # cylinder (track/2) in ch [0-7] and cl[6,7]<-[8,9] - rol $7, %cx + 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 (saved in ax) + # sector num cl[0-5] is sidx % sectors_per_track + 1 + pop %ax inc %al - or %al, %cl + or %al, %cl + # ah = 2 (read), al = 1 sectors mov $0x0201, %ax movb drive_number, %dl int $0x13 - jnc .Lread_ok + jnc read_ok # abort after 3 attempts - decw VAR_ATTEMPTS(%bp) - jz .Lread_fail + decw read_retries + jz read_fail # error detected, reset controller and retry xor %ah, %ah int $0x13 - jmp .Lread_try + jmp read_try -.Lread_fail: +read_fail: mov 4(%bp), %ax jmp abort_read -.Lread_ok: +read_ok: + mov $46, %ax + call print_char + # increment es:bx accordingly (advance es if bx overflows) add $512, %bx - jno 0f + jnc 0f mov %es, %ax add $4096, %ax mov %ax, %es 0: pop %dx pop %cx - add $2, %sp pop %bp ret -str_read_error: .asciz "Failed to read sector: " +str_read_error: .asciz "rderr:" abort_read: - push %ax mov $str_read_error, %si call print_str - - xor %eax, %eax - pop %ax + and $0xffff, %eax call print_num - - cli + mov $10, %al + call print_char hlt -clearscr: - push %es - pushw $0xb800 - pop %es - xor %eax, %eax - xor %di, %di - movl $500, %ecx - rep stosl - pop %es - ret + # expects string pointer in ds:si +print_str: + pusha -cursor_x: .byte 0 +0: mov (%si), %al + cmp $0, %al + jz end + call print_char + inc %si + jmp 0b -# expects string pointer in ds:si -print_str: +end: popa + ret + + # expects character in al +print_char: push %es - pushw $0xb800 + + cmp $10, %ax + jnz 0f + mov $32, %ax + +0: pushw $0xb800 pop %es - xor %di, %di - movb $0, cursor_x + movw cursor_x, %di + shl $1, %di -0: mov (%si), %al mov %al, %es:(%di) movb $7, %es:1(%di) - inc %si - add $2, %di - incb cursor_x - cmp $0, %al - jnz 0b + incw cursor_x pop %es ret -# expects number in eax + # expects number in eax + .global print_num print_num: - # save es - push %es + # save registers + pusha - xor %cx, %cx - movw $numbuf, %si + movw $scratchbuf + scratchbuf_size, %si + movb $0, (%si) mov $10, %ebx - -0: xor %edx, %edx +convloop: + xor %edx, %edx div %ebx add $48, %dl + dec %si mov %dl, (%si) - inc %si - inc %cx cmp $0, %eax - jnz 0b + jnz convloop - # print the backwards string - pushw $0xb800 - pop %es - movb cursor_x, %al - xor %ah, %ah - shl $1, %ax - mov %ax, %di - -0: dec %si - mov (%si), %al - movb %al, %es:(%di) - inc %di - mov $7, %al - movb %al, %es:(%di) - inc %di - dec %cx - jnz 0b + call print_str - # restore es - pop %es + # restore regs + popa ret -drive_number: .byte 0 -numbuf: .space 10 .org 510 .byte 0x55 .byte 0xaa - boot2_addr: