WebSVN – Kolibri OS – Blame – /kernel/trunk/bootloader/boot_fat12.asm

Rev	Author	Line No.	Line
796	shurf	1	; FAT12 boot sector for Kolibri OS
		2	;
		3	; Copyright (C) Alex Nogueira Teixeira
		4	; Copyright (C) Diamond
		5	; Copyright (C) Dmitry Kartashov aka shurf
		6	;
		7	; Distributed under GPL, see file COPYING for details
		8	;
		9	; Version 1.0
		10
2288	clevermous	11	lf equ 0ah
		12	cr equ 0dh
796	shurf	13
2288	clevermous	14	pos_read_tmp equ 0700h ;position for temporary read
		15	boot_program equ 07c00h ;position for boot code
		16	seg_read_kernel equ 01000h ;segment to kernel read
796	shurf	17
2288	clevermous	18	jmp start_program
		19	nop
796	shurf	20
		21	; Boot Sector and BPB Structure
		22	include 'floppy1440.inc'
		23	;include 'floppy2880.inc'
		24	;include 'floppy1680.inc'
		25	;include 'floppy1743.inc'
		26
		27	start_program:
		28
2288	clevermous	29	xor ax, ax
		30	mov ss, ax
		31	mov sp, boot_program
		32	push ss
		33	pop ds
796	shurf	34
2288	clevermous	35	; print loading string
		36	mov si, loading+boot_program
796	shurf	37	loop_loading:
2288	clevermous	38	lodsb
		39	or al, al
		40	jz read_root_directory
		41	mov ah, 0eh
		42	mov bx, 7
		43	int 10h
		44	jmp loop_loading
796	shurf	45
		46	read_root_directory:
2288	clevermous	47	push ss
		48	pop es
796	shurf	49
2288	clevermous	50	; calculate some disk parameters
		51	; - beginning sector of RootDir
		52	mov ax, word [BPB_FATSz16+boot_program]
		53	xor cx, cx
		54	mov cl, byte [BPB_NumFATs+boot_program]
		55	mul cx
		56	add ax, word [BPB_RsvdSecCnt+boot_program]
		57	mov word [FirstRootDirSecNum+boot_program], ax ; 19
		58	mov si, ax
796	shurf	59
2288	clevermous	60	; - count of sectors in RootDir
		61	mov bx, word [BPB_BytsPerSec+boot_program]
		62	mov cl, 5 ; divide ax by 32
		63	shr bx, cl ; bx = directory entries per sector
		64	mov ax, word [BPB_RootEntCnt+boot_program]
		65	xor dx, dx
		66	div bx
		67	mov word [RootDirSecs+boot_program], ax ; 14
796	shurf	68
2288	clevermous	69	; - data start
		70	add si, ax ; add beginning sector of RootDir and count sectors in RootDir
		71	mov word [data_start+boot_program], si ; 33
		72	; reading root directory
		73	; al=count root dir sectrors !!!! TODO: al, max 255 sectors !!!!
		74	mov ah, 2 ; read
		75	push ax
796	shurf	76
2288	clevermous	77	mov ax, word [FirstRootDirSecNum+boot_program]
		78	call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
		79	pop ax
		80	mov bx, pos_read_tmp ; es:bx read buffer
		81	call read_sector
796	shurf	82
2288	clevermous	83	mov si, bx ; read buffer address: es:si
		84	mov ax, [RootDirSecs+boot_program]
		85	mul word [BPB_BytsPerSec+boot_program]
		86	add ax, si ; AX = end of root dir. in buffer pos_read_tmp
796	shurf	87
2288	clevermous	88	; find kernel file in root directory
796	shurf	89	loop_find_dir_entry:
2288	clevermous	90	push si
		91	mov cx, 11
		92	mov di, kernel_name+boot_program
		93	rep cmpsb ; compare es:si and es:di, cx bytes long
		94	pop si
		95	je found_kernel_file
		96	add si, 32 ; next dir. entry
		97	cmp si, ax ; end of directory
		98	jb loop_find_dir_entry
796	shurf	99
		100	file_error_message:
2288	clevermous	101	mov si, error_message+boot_program
796	shurf	102
		103	loop_error_message:
2288	clevermous	104	lodsb
		105	or al, al
		106	jz freeze_pc
		107	mov ah, 0eh
		108	mov bx, 7
		109	int 10h
		110	jmp loop_error_message
796	shurf	111
		112	freeze_pc:
2288	clevermous	113	jmp $ ; endless loop
796	shurf	114
2288	clevermous	115	; === KERNEL FOUND. LOADING... ===
796	shurf	116
		117	found_kernel_file:
2288	clevermous	118	mov bp, [si+01ah] ; first cluster of kernel file
		119	;
		120	mov [cluster1st+boot_program], bp ; starting cluster of kernel file
		121	; <\diamond>
796	shurf	122
2288	clevermous	123	; reading first FAT table
		124	mov ax, word [BPB_RsvdSecCnt+boot_program] ; begin first FAT abs sector number
		125	call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
		126	mov bx, pos_read_tmp ; es:bx read position
		127	mov ah, 2 ; ah=2 (read)
		128	mov al, byte [BPB_FATSz16+boot_program] ; FAT size in sectors (TODO: max 255 sectors)
		129	call read_sector
		130	jc file_error_message ; read error
796	shurf	131
2288	clevermous	132	mov ax, seg_read_kernel
		133	mov es, ax
		134	xor bx, bx ; es:bx = 1000h:0000h
796	shurf	135
		136
2288	clevermous	137	; reading kernel file
796	shurf	138	loop_obtains_kernel_data:
2288	clevermous	139	; read one cluster of file
		140	call obtain_cluster
		141	jc file_error_message ; read error
796	shurf	142
2288	clevermous	143	; add one cluster length to segment:offset
		144	push bx
		145	mov bx, es
		146	mov ax, word [BPB_BytsPerSec+boot_program] ;\
		147	movsx cx, byte [BPB_SecPerClus+boot_program] ; \| !!! TODO: !!!
		148	mul cx ; \| out this from loop !!!
		149	shr ax, 4 ;/
		150	add bx, ax
		151	mov es, bx
		152	pop bx
796	shurf	153
2288	clevermous	154	mov di, bp
		155	shr di, 1
		156	pushf
		157	add di, bp ; di = bp * 1.5
		158	add di, pos_read_tmp
		159	mov ax, [di] ; read next entry from FAT-chain
		160	popf
		161	jc move_4_right
		162	and ax, 0fffh
		163	jmp verify_end_sector
796	shurf	164	move_4_right:
2288	clevermous	165	mov cl, 4
		166	shr ax, cl
796	shurf	167	verify_end_sector:
2288	clevermous	168	cmp ax, 0ff8h ; last cluster
		169	jae execute_kernel
		170	mov bp, ax
		171	jmp loop_obtains_kernel_data
796	shurf	172
		173	execute_kernel:
2288	clevermous	174	;
		175	mov ax, 'KL'
		176	push 0
		177	pop ds
		178	mov si, loader_block+boot_program
		179	;
		180	push word seg_read_kernel
		181	push word 0
		182	retf ; jmp far 1000:0000
796	shurf	183
		184
		185	;------------------------------------------
2288	clevermous	186	; loading cluster from file to es:bx
796	shurf	187	obtain_cluster:
2288	clevermous	188	; bp - cluster number to read
		189	; carry = 0 -> read OK
		190	; carry = 1 -> read ERROR
796	shurf	191
2288	clevermous	192	; print one dot
		193	push bx
		194	mov ax, 0e2eh ; ah=0eh (teletype), al='.'
		195	xor bh, bh
		196	int 10h
		197	pop bx
796	shurf	198
1738	clevermous	199	writesec:
2288	clevermous	200	; convert cluster number to sector number
		201	mov ax, bp ; data cluster to read
		202	sub ax, 2
		203	xor dx, dx
		204	mov dl, byte [BPB_SecPerClus+boot_program]
		205	mul dx
		206	add ax, word [data_start+boot_program]
796	shurf	207
2288	clevermous	208	call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
796	shurf	209	patchhere:
2288	clevermous	210	mov ah, 2 ; ah=2 (read)
		211	mov al, byte [BPB_SecPerClus+boot_program] ; al=(one cluster)
		212	call read_sector
		213	retn
796	shurf	214	;------------------------------------------
		215
		216	;------------------------------------------
2288	clevermous	217	; read sector from disk
796	shurf	218	read_sector:
2288	clevermous	219	push bp
		220	mov bp, 20 ; try 20 times
796	shurf	221	newread:
2288	clevermous	222	dec bp
		223	jz file_error_message
		224	push ax bx cx dx
		225	int 13h
		226	pop dx cx bx ax
		227	jc newread
		228	pop bp
		229	retn
796	shurf	230	;------------------------------------------
2288	clevermous	231	; convert abs. sector number (AX) to BIOS T:H:S
		232	; sector number = (abs.sector%BPB_SecPerTrk)+1
		233	; pre.track number = (abs.sector/BPB_SecPerTrk)
		234	; head number = pre.track number%BPB_NumHeads
		235	; track number = pre.track number/BPB_NumHeads
		236	; Return: cl - sector number
		237	; ch - track number
		238	; dl - drive number (0 = a:)
		239	; dh - head number
796	shurf	240	conv_abs_to_THS:
2288	clevermous	241	push bx
		242	mov bx, word [BPB_SecPerTrk+boot_program]
		243	xor dx, dx
		244	div bx
		245	inc dx
		246	mov cl, dl ; cl = sector number
		247	mov bx, word [BPB_NumHeads+boot_program]
		248	xor dx, dx
		249	div bx
		250	; !!!!!!! ax = track number, dx = head number
		251	mov ch, al ; ch=track number
		252	xchg dh, dl ; dh=head number
		253	mov dl, 0 ; dl=0 (drive 0 (a:))
		254	pop bx
		255	retn
796	shurf	256	;------------------------------------------
		257
2288	clevermous	258	loading db cr,lf,'Starting system ',00h
		259	error_message db 13,10
		260	kernel_name db 'KERNEL MNT ?',cr,lf,00h
		261	FirstRootDirSecNum dw ?
		262	RootDirSecs dw ?
		263	data_start dw ?
796	shurf	264
		265	;
		266	write1st:
2288	clevermous	267	push cs
		268	pop ds
		269	mov byte [patchhere+1+boot_program], 3 ; change ah=2 to ah=3
		270	mov bp, [cluster1st+boot_program]
		271	push 1000h
		272	pop es
		273	xor bx, bx
		274	call writesec
		275	mov byte [patchhere+1+boot_program], 2 ; change back ah=3 to ah=2
		276	retf
		277	cluster1st dw ?
796	shurf	278	loader_block:
2288	clevermous	279	db 1
		280	dw 0
		281	dw write1st+boot_program
		282	dw 0
796	shurf	283	; <\diamond>
		284
2288	clevermous	285	times 0x1fe-$ db 00h
796	shurf	286
2288	clevermous	287	db 55h,0aah ;boot signature

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(root)/kernel/trunk/bootloader/boot_fat12.asm – Rev 2288