fixed stage 1 boot loader problems (worked in some BIOSes across

the 2 times sector/track limit). loading sectors one by one now
fixed also spin down problem after loading stage 2 and the kernel
for now tested with 1.44 MB floppies (both real and in bochs/qemu)

3 files changed, 76 insertions, 26 deletions

diff --git a/src/Makefile b/src/Makefile
index 615c3b6..24d0088 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -14,10 +14,14 @@ all: image.bin kernel.sym
 # + 1 * 512 = 512 for magic.bin
 # (M + N + 1 is the number of sectors to be read in stage 2, as stage 1
 # loads only the first sector, so adapt NOF_LOAD_SECTORS to 38)
+# then we make sure the image has the size of a 1.44 MB floppy
+# (emulators like qemu do some guess work for CHS resolution based
+# on the size of the image)
 image.bin: boot.bin kernel.bin magic.bin
 	cat boot.bin kernel.bin > image.tmp
 	truncate -s 19456 image.tmp
 	cat image.tmp magic.bin > image.bin
+	truncate -s 1474560 image.bin
 	
 boot.bin: boot.asm boot_gdt.asm stage1_functions.asm stage2_functions.asm stage2_switch_mode.asm stage2_a20.asm
 	$(NASM) boot.asm -DMAGIC='"$(MAGIC)"' -f bin -o boot.bin
@@ -94,11 +98,11 @@ clean:
 	-rm -f boot.bin kernel.bin kernel.sym kernel.elf image.bin magic.bin *.o boot.map image.tmp
 
 run-qemu: image.bin
-	qemu-system-i386 -net nic,model=ne2k_pci -d guest_errors -m 32 -drive "file=image.bin,if=ide,format=raw" \
+	qemu-system-i386 -net nic,model=ne2k_pci -d guest_errors -m 32 -drive "file=image.bin,if=floppy,format=raw" \
 		-serial file:serial.log
 
 run-qemu-debug: image.bin
-	qemu-system-i386 -net nic,model=ne2k_pci -S -s -d guest_errors -m 32 -drive "file=image.bin,if=ide,format=raw" \
+	qemu-system-i386 -net nic,model=ne2k_pci -S -s -d guest_errors -m 32 -drive "file=image.bin,if=floppy,format=raw" \
 		-serial file:serial.log
 
 run-bochs:
diff --git a/src/boot.asm b/src/boot.asm
index 9620fcc..3f9c127 100644
--- a/src/boot.asm
+++ b/src/boot.asm
@@ -44,6 +44,10 @@
 ; after the boot sector)	
 	mov dl, [BOOT_DRIVE]
 	call read_from_disk
+	call print_newline
+
+; turn off disk motor
+	call kill_motor
 	
 ; jump over variables and subroutines of stage 1 and execute stage 2
 	jmp stage2
@@ -63,7 +67,7 @@ MESSAGE_BOOT_DRIVE:
 	db "Booting from drive ", 0
 	
 MESSAGE_LOADING_STAGE_2:
-	db "Loading stage 2 boot loader", 13, 10, 0
+	db "Loading stage 2 boot loader and kernel", 0
 	
 BOOT_DRIVE:
 	db 0
diff --git a/src/stage1_functions.asm b/src/stage1_functions.asm
index c9ed1a5..8a73a9b 100644
--- a/src/stage1_functions.asm
+++ b/src/stage1_functions.asm
@@ -4,20 +4,6 @@
 ; subtract 1 here!)
 NOF_LOAD_SECTORS equ 38
 
-; IN bx: begin of memory area to dump
-; IN ax: number of words to dump
-dump_range:
-	mov dx, bx
-	call print_hex
-	mov dx, [bx]
-	call print_hex
-	call print_newline
-	add bx, 2
-	dec ax
-	cmp ax, 0
-	jnz dump_range
-	ret
-
 ; IN dx: hex value to print	
 print_hex:
 	push bx
@@ -104,25 +90,76 @@ current_row:
 	pop ax
 	ret
 
+; data sections used for reading from disk
+SECTORS_TO_LOAD:
+	db NOF_LOAD_SECTORS		; load NOF_LOAD_SECTORS sectors in total
+CURRENT_SECTOR:
+	db 2				; second sector after boot sector
+CURRENT_CYLINDER:
+	db 0
+CURRENT_HEAD:
+	db 0				
+
+; read the whole stage2 and kernel from the disk
 ; IN dl: drive to read from
 read_from_disk:
-	mov ah, 0x02			; read sectors from drive
-	
-	mov al, NOF_LOAD_SECTORS	; read 1 sector
-	mov ch, 0			; select first cylinder
-	mov dh, 0			; first head
-	mov cl, 2			; second sector after boot sector
-	
+
 	mov bx, 0			; where to store the data
 	mov es, bx
 	mov bx, 0x7e00			; 512 bytes after first sector
-		
+
+.read_next_sector:
+
+	call read_one_sector_from_disk
+
+	sub [SECTORS_TO_LOAD], BYTE 1	; one less to load
+	cmp [SECTORS_TO_LOAD], BYTE 0	; finished?
+	je .finished
+
+	add bx, 0x200			; advance write buffer position
+	add [CURRENT_SECTOR], BYTE 1	; next sector
+	cmp [CURRENT_SECTOR], BYTE 0x13	; assuming 18 sectors per track for now
+	je .next_head
+	jmp .read_next_sector
+
+.next_head:
+	mov [CURRENT_SECTOR], BYTE 1	; start from first sector again
+	add [CURRENT_HEAD], BYTE 1	; advance head
+	cmp [CURRENT_HEAD], BYTE 0x02	; 2 heads on floppies
+	je .next_track
+	jmp .read_next_sector
+	
+.next_track:
+	mov [CURRENT_HEAD], BYTE 0	; start from head 0 again
+	add [CURRENT_CYLINDER], BYTE 1	; advance track
+	jmp .read_next_sector
+
+.finished:
+	ret
+
+; Read one sector after the other, if we get illegal parameter
+; errors we assume we have gone over the limit of number of
+; sectors per cylinder. This avoids to probe for this number with
+; shacky BIOS functions or with probing (as LILO does). It's not
+; very efficient though..
+; IN dl: drive to read from
+read_one_sector_from_disk:
+	mov ah, 0x02			; read sectors from drive
+	
+	mov al, 1			; read 1 sector
+	mov ch, BYTE [CURRENT_CYLINDER]
+	mov dh, BYTE [CURRENT_HEAD]
+	mov cl, BYTE [CURRENT_SECTOR]
+			
 	int 0x13
 	
 	jc .read_error
 	
-	cmp al, NOF_LOAD_SECTORS	; 1 sector read?
+	cmp al, 1			; 1 sector read?
 	jne .short_read			; if not, short read
+
+	mov al, '.'
+	call print_char
 	
 	ret
 	
@@ -139,3 +176,8 @@ read_from_disk:
 	call print_string
 	jmp $
 
+kill_motor:
+	mov	dx, 0x3F2
+	mov	al, 0x00
+	out	dx, al
+        ret