ldarch = -m elf_i386
endif
+floppy.img: $(bin)
+ dd if=/dev/zero of=$@ bs=512 count=2880
+ dd if=$< of=$@ conv=notrunc
+
$(bin): $(elf)
objcopy -O binary $< $@
.PHONY: run
run: $(bin)
- qemu-system-i386 -fda $(bin)
+ qemu-system-i386 -fda floppy.img
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
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
+
# 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 $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
+str_read_error: .asciz "Failed to read sector: "
+
+abort_read:
+ push %ax
+ mov $str_read_error, %si
+ call print_str
+
+ xor %eax, %eax
+ pop %ax
+ call print_num
+
+ cli
+ hlt
+
clearscr:
push %es
pushw $0xb800
pop %es
ret
+cursor_x: .byte 0
+
+# expects string pointer in ds:si
+print_str:
+ push %es
+ pushw $0xb800
+ pop %es
+ xor %di, %di
+ movb $0, cursor_x
+
+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 %es
+ ret
+
# expects number in eax
print_num:
# save es
# 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