.code16
.section .boot,"a"
+ .set scratchbuf, 0x7bf0
+ .set scratchbuf_size, 16
+
+boot:
cli
cld
- # move stack to the top of 512k
- mov $0x7000, %ax
+ # move stack to just below the code
+ xor %ax, %ax
mov %ax, %ss
- xor %sp, %sp
+ mov $0x7bf0, %sp
# use the code segment for data access
mov %cs, %ax
mov %ax, %ds
mov %dl, drive_number
- call clearscr
+ call setup_serial
- mov $_boot2_size, %eax
- call print_num
+ 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 $loading_msg2, %si
+ call print_str
+
mov %eax, %ebx
shr $9, %eax
and $0x1ff, %ebx
jz 0f
- inc %eax
+ inc %ax
0: pushw %ax
pushw $1
# set es to the start of the destination buffer to allow reading in
shr $4, %bx
mov %bx, %es
xor %bx, %bx
- call read_sect
+ call read_sectors
jmp boot2_addr
- cli
- hlt
-
.set SECT_PER_TRACK, 18
.set ARG_NSECT, 6
.set ARG_SIDX, 4
-# read_sect(first, num)
-read_sect:
+loading_msg: .asciz "Loading "
+loading_msg2: .asciz " bytes\n"
+
+sect_per_track: .short 18
+num_cylinders: .short 80
+num_heads: .short 2
+heads_mask: .byte 1
+
+get_drive_chs:
+ movb drive_number, %dl
+ mov $8, %ah
+ int $0x13
+ jnc .Lok
+ ret
+
+.Lok: mov %ch, %al
+ mov %cl, %ah
+ rol $2, %ah
+ and $0x3ff, %ax
+ mov %ax, num_cylinders
+
+ mov %cx, sect_per_track
+ andw $0x3f, sect_per_track
+
+ shr $8, %dx
+ mov %dx, num_heads
+ dec %dl
+ mov %dl, heads_mask
+
+ ret
+
+# read_sectors(first, num)
+read_sectors:
push %bp
mov %sp, %bp
mov ARG_SIDX(%bp), %ax
- mov ARG_NSECT(%bp), %cx
+ xor %cx, %cx
jmp 1f
0: push %ax
call read_sector
- add $2, %sp
+ pop %ax
+ inc %ax
+ inc %cx
1: cmp ARG_NSECT(%bp), %cx
jnz 0b
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)
+
+.Lread_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
+
+ # abort after 3 attempts
+ decw VAR_ATTEMPTS(%bp)
+ jz .Lread_fail
+
+ # error detected, reset controller and retry
+ xor %ah, %ah
+ int $0x13
+ jmp .Lread_try
+
+.Lread_fail:
+ mov 4(%bp), %ax
+ jmp abort_read
+
+.Lread_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
- pop %dx
+0: pop %dx
pop %cx
+ add $2, %sp
pop %bp
ret
-clearscr:
+str_read_error: .asciz "read error, sector: "
+
+abort_read:
+ mov $str_read_error, %si
+ call print_str_num16
+ hlt
+
+ # prints a string (ds:si) followed by a number (eax)
+print_str_num:
+ push %eax
+ call print_str
+ pop %eax
+ call print_num
+ mov $10, %al
+ call ser_putchar
+ ret
+
+print_str_num16:
+ push %eax
+ and $0xffff, %eax
+ call print_str_num
+ pop %eax
+ ret
+
+ # expects string pointer in ds:si
+print_str:
+ pusha
+
+0: mov (%si), %al
+ cmp $0, %al
+ jz .Lend
+ call print_char
+ inc %si
+ jmp 0b
+
+.Lend: popa
+ ret
+
+ # expects character in al
+print_char:
push %es
pushw $0xb800
pop %es
- xor %eax, %eax
- xor %di, %di
- movl $500, %ecx
- rep stosl
+ movw cursor_x, %di
+ shl $1, %di
+
+ mov %al, %es:(%di)
+ movb $7, %es:1(%di)
+ incw cursor_x
+
+ call ser_putchar
pop %es
ret
-# expects number in eax
+cursor_x: .short 0
+
+ # 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
+.Lconvloop:
+ xor %edx, %edx
div %ebx
add $48, %dl
+ dec %si
mov %dl, (%si)
- inc %si
- inc %cx
cmp $0, %eax
- jnz 0b
+ jnz .Lconvloop
- # print the backwards string
- pushw $0xb800
- pop %es
- xor %di, %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
+
+ .set UART_DATA, 0x3f8
+ .set UART_DIVLO, 0x3f8
+ .set UART_DIVHI, 0x3f9
+ .set UART_FIFO, 0x3fa
+ .set UART_LCTL, 0x3fb
+ .set UART_MCTL, 0x3fc
+ .set UART_LSTAT, 0x3fd
+ .set DIV_9600, 115200 / 9600
+ .set LCTL_8N1, 0x03
+ .set LCTL_DLAB, 0x80
+ .set FIFO_ENABLE, 0x01
+ .set FIFO_SEND_CLEAR, 0x04
+ .set FIFO_RECV_CLEAR, 0x02
+ .set MCTL_DTR, 0x01
+ .set MCTL_RTS, 0x02
+ .set MCTL_OUT2, 0x08
+ .set LST_TREG_EMPTY, 0x20
+
+setup_serial:
+ # set clock divisor
+ mov $LCTL_DLAB, %al
+ mov $UART_LCTL, %dx
+ out %al, %dx
+ mov $DIV_9600, %ax
+ mov $UART_DIVLO, %dx
+ out %al, %dx
+ shr $8, %ax
+ mov $UART_DIVHI, %dx
+ out %al, %dx
+ # set format 8n1
+ mov $LCTL_8N1, %al
+ mov $UART_LCTL, %dx
+ out %al, %dx
+ # clear and enable fifo
+ mov $FIFO_ENABLE, %al
+ or $FIFO_SEND_CLEAR, %al
+ or $FIFO_RECV_CLEAR, %al
+ mov $UART_FIFO, %dx
+ out %al, %dx
+ # assert RTS and DTR
+ mov $MCTL_DTR, %al
+ or $MCTL_RTS, %al
+ or $MCTL_OUT2, %al
+ mov $UART_MCTL, %dx
+ out %al, %dx
+ ret
+
+ # expects a character in al
+ .global ser_putchar
+ser_putchar:
+ push %dx
+
+ cmp $10, %al
+ jnz 0f
+ push %ax
+ mov $13, %al
+ call ser_putchar
+ pop %ax
+
+0: mov %al, %ah
+ # wait until the transmit register is empty
+ mov $UART_LSTAT, %dx
+.Lwait: in %dx, %al
+ and $LST_TREG_EMPTY, %al
+ jz .Lwait
+ mov $UART_DATA, %dx
+ mov %ah, %al
+ out %al, %dx
+
+ pop %dx
ret
+
drive_number: .byte 0
-numbuf: .space 10
.org 510
.byte 0x55
.byte 0xaa
projects / bootcensus / blobdiff