X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;f=src%2Fboot%2Fboot.s;h=499c38637e7936b7391df7cea937a9ed24ade657;hb=ced643ce94dafd3d31e121435a40a967993e2be5;hp=e3fd206ba416396c23b0df24bb4e83772437d19c;hpb=e5b5905eb3134a409638a5a20462000ef159e1e6;p=bootcensus

diff --git a/src/boot/boot.s b/src/boot/boot.s
index e3fd206..499c386 100644
--- a/src/boot/boot.s
+++ b/src/boot/boot.s
@@ -1,37 +1,162 @@
 	.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
+	cli
+	cld
+	# move stack to the top of 512k
+	mov $0x7000, %ax
+	mov %ax, %ss
+	xor %sp, %sp
+	# use the code segment for data access
+	mov %cs, %ax
+	mov %ax, %ds
+	mov %ax, %es
+
+	mov %dl, drive_number
+
+	call clearscr
+
+	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
+	and $0x1ff, %ebx
+	jz 0f
+	inc %eax
+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_sect
+	jmp boot2_addr
 
 	cli
 	hlt
 
+	.set SECT_PER_TRACK, 18
+
+	.set ARG_NSECT, 6
+	.set ARG_SIDX, 4
+
+# read_sect(first, num)
+read_sect:
+	push %bp
+	mov %sp, %bp
+
+	mov ARG_SIDX(%bp), %ax
+	mov ARG_NSECT(%bp), %cx
+
+	jmp 1f
+0:	push %ax
+	call read_sector
+	add $2, %sp
+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
+
+	# 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 in ax
+	mov %dx, %ax
+	# 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
+	ror $2, %cl
+	and $0xc0, %cl
+	# sector num cl[0-5] is sidx % sectors_per_track (saved in ax)
+	inc %al
+	or %al, %cl 
+	# ah = 2 (read), al = 1 sectors
+	mov $0x0201, %ax
+	movb drive_number, %dl
+	int $0x13
+
+	# increment es:bx accordingly (advance es if bx overflows)
+	add $512, %bx
+	jno 0f
+	mov %es, %ax
+	add $4096, %ax
+	mov %ax, %es
+
+	pop %dx
+	pop %cx
+	pop %bp
+	ret
+
+clearscr:
+	push %es
+	pushw $0xb800
+	pop %es
+	xor %eax, %eax
+	xor %di, %di
+	movl $500, %ecx
+	rep stosl
+	pop %es
+	ret
+
+# expects number in eax
+print_num:
+	# save es
+	push %es
+
+	xor %cx, %cx
+	movw $numbuf, %si
+	mov $10, %ebx
+
+0:	xor %edx, %edx
+	div %ebx
+	add $48, %dl
+	mov %dl, (%si)
+	inc %si
+	inc %cx
+	cmp $0, %eax
+	jnz 0b
+
+	# 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
+
+	# restore es
+	pop %es
+	ret
+
+drive_number: .byte 0
+numbuf: .space 10
 	.org 510
 	.byte 0x55
 	.byte 0xaa
+
+boot2_addr: