+# pcboot - bootable PC demo/game kernel
+# Copyright (C) 2018-2019 John Tsiombikas <nuclear@member.fsf.org>
+#
+# 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 <https://www.gnu.org/licenses/>.
+
.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:
projects / bootcensus / blobdiff