From eea5bf4b859eb56c5772c58ca54937a90a10e7ee Mon Sep 17 00:00:00 2001
From: Andreas Baumann <mail@andreasbaumann.cc>
Date: Sat, 10 Jun 2017 20:55:56 +0200
Subject: moved bootloader to subdirectory

---
 src/boot/stage2_real_functions.asm | 169 +++++++++++++++++++++++++++++++++++++
 1 file changed, 169 insertions(+)
 create mode 100644 src/boot/stage2_real_functions.asm

(limited to 'src/boot/stage2_real_functions.asm')

diff --git a/src/boot/stage2_real_functions.asm b/src/boot/stage2_real_functions.asm
new file mode 100644
index 0000000..d49bfce
--- /dev/null
+++ b/src/boot/stage2_real_functions.asm
@@ -0,0 +1,169 @@
+; number of sectors to be read for the kernel itself
+; (note: the first sector gets loaded by the BIOS, the
+; next 3 sectors are read by the simple stage 1 loader,
+; so subtract 3 here!)
+NOF_LOAD_SECTORS equ 37
+
+; data sections used for reading the kernel from disk
+SECTORS_PER_CYLINDER:
+	db 0x3F				; detect parameters enters the correct value here (sectors + 1)
+					; if detection fails, force int13 to read ahead
+NOF_HEADS:
+	db 0x01				; number of heads + 1
+SECTORS_TO_LOAD:
+	db NOF_LOAD_SECTORS		; load NOF_LOAD_SECTORS sectors in total
+CURRENT_SECTOR:
+	db 5				; first sector after stage 2
+CURRENT_CYLINDER:
+	db 0
+CURRENT_HEAD:
+	db 0				
+
+; detect disk geometry
+; IN dl: drive
+detect_disk_geometry:
+	mov dx, 0
+	mov es, dx
+	mov ah, 0x08
+	int 0x13
+	jc .error
+	jmp .ok
+
+.error:
+	mov si, DISK_ERROR
+	call print_string
+	mov dh, 0
+	mov dl, ah
+	call print_hex
+	ret
+	
+.ok:
+	add dh, 1
+	mov [NOF_HEADS], BYTE dh
+	call print_hex
+	mov dx, cx
+	call print_hex
+	and cl, 0x3F
+	add cl, 1
+	mov [SECTORS_PER_CYLINDER], BYTE cl
+	ret
+
+probe_and_fix_disk_geometry:
+	mov cl, 0x1			; from 1 to 63
+	mov BYTE [SECTORS_PER_CYLINDER], cl
+
+.loop:
+	mov dl, [BOOT_DRIVE]
+	mov ah, 0x02			; read sectors from drive
+	mov al, 1			; read 1 sector
+	mov cl, BYTE [SECTORS_PER_CYLINDER]
+	mov ch, BYTE 0
+	mov dh, BYTE 0
+			
+	int 0x13
+	
+	jnc .next_sector		; on error, remeber cl being the highest sector
+
+.fix_heads:
+	cmp [NOF_HEADS], BYTE 0		; 0 heads, the BIOS is playing tricks to us!
+	je .illegal_heads
+	jmp .end
+
+.illegal_heads:
+	mov [NOF_HEADS], BYTE 1
+	jmp .end
+
+.next_sector:
+	mov cl, BYTE [SECTORS_PER_CYLINDER]
+	inc cl				; next sector
+	mov BYTE [SECTORS_PER_CYLINDER], cl
+	cmp cl, 0x40			; to a max of 63, if so, this is the default
+	jbe .loop
+	jmp .fix_heads
+
+.end:
+	ret
+
+; read the whole stage2 and kernel from the disk
+; IN dl: drive to read from
+read_from_disk:
+
+	mov bx, 0			; where to store the data
+	mov es, bx
+	mov bx, 0x8400			; 2'048 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
+	mov ch, [SECTORS_PER_CYLINDER]
+	cmp [CURRENT_SECTOR], ch	; after the end of the current track?
+	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
+	mov ch, [NOF_HEADS]
+	cmp [CURRENT_HEAD], ch		; after the number of heads?
+	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, 1			; 1 sector read?
+	jne .short_read			; if not, short read
+
+	mov al, '.'
+	call print_char
+	
+	ret
+	
+.read_error:
+	mov si, DISK_ERROR
+	call print_string
+	mov dh, 0
+	mov dl, ah
+	call print_hex
+	jmp $
+
+.short_read:
+	mov si, SHORT_READ
+	call print_string
+	jmp $
+
+kill_motor:
+	mov dx, 0x3F2
+	mov al, 0x00
+	out dx, al
+        ret
-- 
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