X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot.s;h=ac4a424c5ce713814642489e4ccd10152c7cc682;hp=499c38637e7936b7391df7cea937a9ed24ade657;hb=07db0aabb3ad8dbb0a3cee2d3837dd93792ae825;hpb=ced643ce94dafd3d31e121435a40a967993e2be5

diff --git a/src/boot/boot.s b/src/boot/boot.s
index 499c386..ac4a424 100644
--- a/src/boot/boot.s
+++ b/src/boot/boot.s
@@ -3,10 +3,10 @@
 
 	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
@@ -25,7 +25,7 @@
 	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
@@ -34,7 +34,7 @@
 	shr $4, %bx
 	mov %bx, %es
 	xor %bx, %bx
-	call read_sect
+	call read_sectors
 	jmp boot2_addr
 
 	cli
@@ -45,31 +45,39 @@
 	.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
@@ -92,7 +100,22 @@ read_sector:
 	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
@@ -100,11 +123,26 @@ read_sector:
 	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
@@ -116,6 +154,28 @@ clearscr:
 	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
@@ -137,7 +197,10 @@ print_num:
 	# 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