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 $0x7c00, %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
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
.set ARG_NSECT, 6
.set ARG_SIDX, 4
-# read_sect(first, num)
-read_sect:
+# 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
+str_rdsec_msg: .asciz "rdsec: "
+str_cyl_msg: .asciz " C "
+str_head_msg: .asciz " H "
+str_sec_msg: .asciz " S "
+
# 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
+ mov $str_rdsec_msg, %si
+ call print_str_num16
+
xor %dx, %dx
mov $SECT_PER_TRACK, %cx
div %cx
and $0xc0, %cl
# sector num cl[0-5] is sidx % sectors_per_track (saved in ax)
inc %al
- or %al, %cl
+ or %al, %cl
+
+ mov $str_cyl_msg, %si
+ mov %cx, %ax
+ rol $2, %al
+ and $3, %al
+ ror $8, %ax
+ call print_str_num16
+
+ mov $str_head_msg, %si
+ xor %ax, %ax
+ mov %dh, %al
+ call print_str_num16
+
+ mov $str_sec_msg, %si
+ mov %cl, %al
+ and $0x3f, %ax
+ call print_str_num16
+
# 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:
# increment es:bx accordingly (advance es if bx overflows)
add $512, %bx
jno 0f
add $4096, %ax
mov %ax, %es
- pop %dx
+0: pop %dx
pop %cx
+ add $2, %sp
pop %bp
ret
-clearscr:
+str_read_error: .asciz "err read sector: "
+
+abort_read:
+ mov $str_read_error, %si
+ call print_str_num16
+ cli
+ hlt
+
+cursor_x: .byte 0
+
+ # 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:
push %es
+ pusha
+
pushw $0xb800
pop %es
- xor %eax, %eax
xor %di, %di
- movl $500, %ecx
- rep stosl
+ movb $0, cursor_x
+
+ push %si
+
+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
+
+ pop %si
+ call ser_putstr
+
+ popa
pop %es
ret
-# expects number in eax
+ # expects number in eax
print_num:
- # save es
+ # save registers
push %es
+ pusha
xor %cx, %cx
movw $numbuf, %si
# print the backwards string
pushw $0xb800
pop %es
- xor %di, %di
+ movb cursor_x, %al
+ xor %ah, %ah
+ shl $1, %ax
+ mov %ax, %di
0: dec %si
mov (%si), %al
movb %al, %es:(%di)
+ call ser_putchar
inc %di
mov $7, %al
movb %al, %es:(%di)
dec %cx
jnz 0b
- # restore es
+ # restore regs
+ popa
pop %es
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
+ser_putchar:
+ push %dx
+
+ mov %al, %ah
+ # wait until the transmit register is empty
+ mov $UART_LSTAT, %dx
+0: in %dx, %al
+ and $LST_TREG_EMPTY, %al
+ jz 0b
+ mov $UART_DATA, %dx
+ mov %ah, %al
+ out %al, %dx
+
+ pop %dx
+ ret
+
+ # expects a string in ds:si
+ser_putstr:
+ mov (%si), %al
+ cmp $0, %al
+ jz 0f
+ call ser_putchar
+ inc %si
+ jmp ser_putstr
+0: ret
+
+
drive_number: .byte 0
-numbuf: .space 10
+numbuf: .space 8
.org 510
.byte 0x55
.byte 0xaa
projects / bootcensus / blobdiff