[apple/boot.git] / i386 / boot1 / boot1.asm

; boot1.asm - boot1 written for turbo assembler, since gas only\r
; generates 32 bit code and this must run in real mode.
; To compile as hard disk boot1:
;	tasm /m3 /dBOOTDEV=HDISK boot1
;	tlink boot1
;	exe2bin boot1
;	ren boot1.bin boot1
; To compile as floppy boot1f:
;	tasm /m3 /dBOOTDEV=FLOPPY boot1 ,boot1f
;	tlink boot1f
;	exe2bin boot1f
;	ren boot1f.bin boot1f
\r
;***********************************************************************\r
;	This is the code for the NeXT boot1 bootsector.
;***********************************************************************\r
\r
	P486			;enable i386 instructions\r
	IDEAL\r
	SEGMENT CSEG\r
	ASSUME CS:CSEG,DS:CSEG\r
\r
	SDEBUG = 0\r
\r
;BOOTSEG		=	100h	; boot will be loaded at 4k\r
;BOOTOFF		=	0000h
BOOTSEG		=	00h
BOOTOFF		=	1000h
BUFSZ		=	2000h	; 8K disk transfer buffer\r
\r
; FDISK partition table in sector 0\r
PARTSTART	=	1beh	; starting address of partition table\r
NUMPART		=	4	; number of partitions in partition table\r
PARTSZ		=	16	; each partition table entry is 16 bytes\r
BOOT_IND	=	0	; offset of boot indicator in partition table\r
BEG_HEAD	=	1	; offset of beginning head\r
BEG_SEC		= 	2	; offset of beginning sector\r
BEG_CYL		=	3	; offset of beginning cylinder\r
NAME_OFFSET	=	4	; offset of partition name\r
PARTSEC		=	8	; offset of partition sector specifier\r
NEXTNAME	=	0A7h	; value of boot_ind, means bootable partition\r
\r
LOADSZ		=	88	; maxiumum possible size of unix boot\r- 44k
\r
FLOPPY		=	0
HDISK		=	80h

;BOOTDEV	=	?	; set to 00h for floppy, 80h for hard disk
				; (use a command line switch to set)

; NeXT disk label\r
DISKLABEL	=	15	; sector num of 2nd disk label, 1st is trashed by bootsec\r
DL_DISKTAB	=	44\r
\r
; We support disk label version 3 "3Vld" in our little endian world\r
DL_V3		= 	33566c64h\r
\r
; NeXT disktab\r
DT_SECSIZE	=	48\r
DT_BOOT0_BLKNO	=	80\r
\r\r
; This code is a replacement for boot1.  It is loaded at 0x0:0x7c00\r
\r
start:\r
	mov	ax,BOOTSEG
	cli			; interrupts off\r
	mov	ss,ax		; set up stack seg\r
	mov	sp,0fff0h\r
	sti			; reenable interrupts\r

	xor	ax,ax
	mov	es,ax
	mov	ds,ax
	mov	si,7C00h
	cld			; so pointers will get updated\r
	mov	di,0E000h	; relocate boot program to 0xE000\r
	mov	cx,100h		; copy 256x2 bytes\r
	repnz	movsw		; move it\r
	off1	=  0E000h + (a1 - start)\r
	jmp	FAR 0000:off1	; jump to a1 in relocated place\r

a1:\r
	mov	ax,0E00h\r
	mov	ds,ax\r
	mov	ax,BOOTSEG\r
	mov	es,ax\r
\r
	; load the boot loader (boot2) into BOOTSEG:BUFSZ\r
	call	loadboot\r
\r
	; ljmp to the second stage boot loader (boot2).\r
	; After ljmp, cs is BOOTSEG and boot1 (BUFSZ bytes) will be used\r
	; as an internal buffer "intbuf".\r
\r
	xor	edx,edx		; bootdev = 0 for hard disk\r
IF	( BOOTDEV EQ FLOPPY )
	inc	edx		; bootdev = 1 for floppy disk
ENDIF

	;boot2 immediately follows disk buffer;  4K + BUFSZ\r
	jmp	FAR  BOOTSEG:(BOOTOFF + BUFSZ)	
				; jump to boot2 in loaded location\r
\r
\r
\r
loadboot:\r
	mov	si, OFFSET intro\r
	call	message		; display intro message\r
\r
	; load second stage boot from fixed disk\r
	; get boot drive parameters\r
	; Note: I believe that the bootsector read may not be necessary;\r
	; at least some blk0 bootsectors leave a pointer to the active\r
	; partition entry in si (assuming there was another blk0 bootsec)\r
\r
	call	getinfo\r
\r	
IF	( BOOTDEV EQ HDISK )
	
	; read sector 0 into BOOTSEG:0 by using BIOS call (INT 13H 02H)\r
	; this gets info on the disk's actual partition table\r
	; However, in the case of multiple partitions, this may not\r
	; be the same as the sector with the code here.\r
\r
	mov	di,5		; try 5 times to read bootsector\r
\r
retry_disk:\r
		xor	bx, bx		; buffer is BOOTSEG:0\r
		mov	ax,201h\r
		mov	cx,bx\r
		mov	dx,bx\r
		mov	bx,BOOTOFF	; actually, it's 0:BOOTOFF
		inc	cx		; cyl 0, sector 1\r
		mov	dl,BOOTDEV	; target 0, head 0\r
\r
		push	di\r
		int	13h		; read the bootsector\r
		pop	di\r
\r
		jnb	read_success1\r
\r
		; woops, bios failed to read sector\r
		xor	ax,ax\r
		int	13h		; reset disk\r
		dec	di\r
		jne	retry_disk\r
\r
		jmp	read_error	; disk failed\r
\r
\r
read_success1:		; find the NeXT partition\r
	mov	bx,PARTSTART\r
	mov	cx,NUMPART\r
\r
again:\r
	mov	al, [es:(bx+BOOTOFF)+NAME_OFFSET]
					; get partition name\r
	cmp	al, NEXTNAME		; is it NeXT partition?\r
	jne	cont			; nope, keep looking\r
\r
foundNextPart:				; found it, get label location\r
\r
	mov	eax, [es:(bx+BOOTOFF)+PARTSEC]
					; offset to NeXT partition\r
	add	eax, DISKLABEL		; add offset to the label\r
	jmp	getLabl			; fetch that label\r
\r
cont:\r
	add	bx, PARTSZ\r
	loop	again			; if more part table entries,
					; keep looking\r
\r
	; fall through, didn't find NeXT disk partition entry\r
\r
no_fdisk:\r
ENDIF
	; Read NeXT disk label\r
	mov	eax, DISKLABEL		; Get block number of label\r
getLabl:\r
	mov	bx,BOOTOFF		; read into load area
	mov	cx,1
	call	readSectors\r
\r
	; we used to think about testing the disk label version here...\r

	mov	bx,BOOTOFF		; point to beginning of label
\r
	; Use values from label to read entire boot program\r
	; Get block number of boot\r
	; Get dl_secsize and dl_boot0_blkno[0]\r
	mov	edx, [es:(bx + DL_DISKTAB+DT_SECSIZE)]\r
	bswap	edx			; edx -> sector size\r
\r
	mov	eax, [es:(bx + DL_DISKTAB+DT_BOOT0_BLKNO)]\r
	bswap	eax			; eax -> block #\r

	; Compute dl_secsize * dt_boot0_blkno[0] / 512\r
	shr	edx, 9			; divide dl_secsize by 512\r
	mul	edx			; multiply boot block loc
					; by dl_secsize/512\r
					; eax has secno\r
	mov	bx, (BUFSZ + BOOTOFF)	; read boot2 into BOOTSEG:BUFSZ\r
	mov	edi, LOADSZ		; read this many sectors\r
nexsec:\r
		push	eax		; push sector #\r
		push	bx		; push buffer address\r
		mov	ecx, edi	; max number of sectors to read
		
		call	readSectors\r
		pop	bx\r
		pop	eax\r
		add	eax, ecx	; add number of sectors read
		sub	di, cx
		shl	cx, 9		; multiply by 512 bytes per sector
		add	bx, cx

	cmp di, 0
	jne	nexsec\r

	ret\r
\r
spt:	DW	0			; sectors;track (one-based)\r
spc:	DW	0			; tracks;cylinder (zero-based)\r
nsec:	DW	0			; number of sectors to read
\r
readSectors:	; eax has starting block #, bx has offset from BOOTSEG\r
		; cx has maximum number of sectors to read
		; Trashes ax, bx, cx, dx\r
\r
	; BIOS call "INT 0x13 Function 0x2" to read sectors\r
	;	ah = 0x2	al = number of sectors\r
	;	ch = cylinder	cl = sector\r
	;	dh = head	dl = drive (0x80=hard disk, 0=floppy disk)\r
	;	es:bx = segment:offset of buffer\r

IF	( BOOTDEV EQ FLOPPY )
		push	eax\r
		mov	al,'.'\r
		call	putchr\r
		pop	eax\r
ENDIF\r
\r
	push	bx			; save offset\r
	mov [WORD nsec], cx
\r
	mov	ebx, eax		; bx -> block #\r
	xor	ecx, ecx\r
	mov	cx, [WORD spc]		; cx -> sectors/cyl\r
\r
	xor	edx,edx			; prepare for division\r
	div	ecx			; eax = cyl, edx=remainder\r
	push	ax			; save cylinder #, sec/spc\r
\r
	mov	eax, edx\r
	mov	cx,  [WORD spt]		; ecx -> sectors/track\r
	xor	edx,edx			; prepare for division\r
	div	ecx			; eax = head\r
	push	ax			; save head, (secspc)/spt\r
\r
	mov	eax, ebx		; reload block #\r
	xor	edx, edx		; prepare for division\r
	div	ecx			; edx has sector #\r
\r
	sub	cx, dx 			;cx now has number of sectors to read
	cmp	cx, [WORD nsec]
	jge	last			; use the minimum of bx and cx
	mov	[WORD nsec], cx
last:

	mov	cx, dx			; cl -> sector\r
	inc	cl			; starts @ 1\r
	pop	ax			; get head\r
	mov	dh, al			; dh -> head\r
\r
	pop	ax			; get cyl\r
	mov	ch, al			; ch -> cyl\r
	mov	dl, BOOTDEV		; floppy disk\r
\r
	xor	al,al\r
	shr	ax,2\r
	or	cl,al			; retain pesky big cyl bits\r

;	mov	al, 1			; get # of sectors\r
;pop ax ; number of sectors to read
mov ax, [WORD nsec]
	pop	bx			; get buffer\r
	mov	ah, 2			; bios read function\r
	\r
	int	13h\r
\r
	jb	read_error\r
mov cx, [WORD nsec] ; return number of sectors read
	ret\r
\r
\r
getinfo:	; get some drive parameters\r
	mov	dl, BOOTDEV		; boot drive is drive C\r
	mov	ah, 8h\r
	push	es
	int	13h\r
	pop	es
\r
	mov	al, dh			; max head #\r
	inc	al			; al -> tracks/cyl\r
	and	cx, 3fh			; cl -> secs/track\r
	mul	cl			; ax -> secs/cyl\r
	mov	[WORD spc], ax\r
	mov	[WORD spt], cx\r
\r
	ret\r
\r
\r
message:				; write the error message in ds:esi
					; to console\r
	push	es\r
	mov	ax,ds\r
	mov	es,ax\r
\r
	mov	bx, 1			; bh=0, bl=1 (blue)\r
	cld\r
\r
nextb:\r
	lodsb				; load a byte into al\r
	cmp	al, 0\r
	je	done\r
	mov	ah, 0eh			; bios int 10, function 0xe\r
	int	10h			; bios display a byte in tty mode\r
	jmp	nextb\r
done:	pop	es\r
	ret\r
\r
putchr:\r
	push	bx\r
	mov	bx, 1			; bh=0, bl=1 (blue)\r
	mov	ah, 0eh			; bios int 10, function 0xe\r
	int	10h			; bios display a byte in tty mode\r
	pop	bx\r
	ret\r

IF	SDEBUG\r
hexout:\r				; print ebx as hex number
	push	cx\r
	push	ax\r
	mov	cx,8			;output 8 nibbles\r
\r
htop:\r
		rol	ebx,4\r
		mov	al,bl\r
		and	al,0fh\r
		cmp	al,0ah\r
		jb	o_digit\r
		add	al,'A'-10\r
		jmp	o_print\r
o_digit:	add	al,'0'\r
o_print:	call	putchr\r
		dec	cx\r
		jne	htop\r
;	mov	al,10\r
;	call	putchr\r
;	mov	al,13\r
;	call	putchr\r
	mov	al,' '
	call	putchr
	pop	ax\r
	pop	cx\r
	ret\r
ENDIF\r
\r
\r
read_error:\r
	mov	si, OFFSET eread\r
boot_exit:				; boot_exit: write error message and halt\r
	call	message			; display error message\r
halt:	jmp	halt\r
\r
\r
intro:	db	10,'NEXTSTEP boot1 vXX.XX.XX.XX.XX',10,13,0\r
eread:	db	'Read error',10,13,0\r

; the last 2 bytes in the sector contain the signature\r
d1:\r
	a2 = 510 - (d1 - start)\r
	DB a2 dup (0)\r
	DW 0AA55h\r
	ENDS\r
	END\r
Commit	Line	Data
14c7c974 A	1	; boot1.asm - boot1 written for turbo assembler, since gas only\r
	2	; generates 32 bit code and this must run in real mode.
	3	; To compile as hard disk boot1:
	4	; tasm /m3 /dBOOTDEV=HDISK boot1
	5	; tlink boot1
	6	; exe2bin boot1
	7	; ren boot1.bin boot1
	8	; To compile as floppy boot1f:
	9	; tasm /m3 /dBOOTDEV=FLOPPY boot1 ,boot1f
	10	; tlink boot1f
	11	; exe2bin boot1f
	12	; ren boot1f.bin boot1f
	13	\r
	14	;***********************************************************************\r
	15	; This is the code for the NeXT boot1 bootsector.
	16	;***********************************************************************\r
	17	\r
	18	P486 ;enable i386 instructions\r
	19	IDEAL\r
	20	SEGMENT CSEG\r
	21	ASSUME CS:CSEG,DS:CSEG\r
	22	\r
	23	SDEBUG = 0\r
	24	\r
	25	;BOOTSEG = 100h ; boot will be loaded at 4k\r
	26	;BOOTOFF = 0000h
	27	BOOTSEG = 00h
	28	BOOTOFF = 1000h
	29	BUFSZ = 2000h ; 8K disk transfer buffer\r
	30	\r
	31	; FDISK partition table in sector 0\r
	32	PARTSTART = 1beh ; starting address of partition table\r
	33	NUMPART = 4 ; number of partitions in partition table\r
	34	PARTSZ = 16 ; each partition table entry is 16 bytes\r
	35	BOOT_IND = 0 ; offset of boot indicator in partition table\r
	36	BEG_HEAD = 1 ; offset of beginning head\r
	37	BEG_SEC = 2 ; offset of beginning sector\r
	38	BEG_CYL = 3 ; offset of beginning cylinder\r
	39	NAME_OFFSET = 4 ; offset of partition name\r
	40	PARTSEC = 8 ; offset of partition sector specifier\r
	41	NEXTNAME = 0A7h ; value of boot_ind, means bootable partition\r
	42	\r
	43	LOADSZ = 88 ; maxiumum possible size of unix boot\r- 44k
	44	\r
	45	FLOPPY = 0
	46	HDISK = 80h
	47
	48	;BOOTDEV = ? ; set to 00h for floppy, 80h for hard disk
	49	; (use a command line switch to set)
	50
	51	; NeXT disk label\r
	52	DISKLABEL = 15 ; sector num of 2nd disk label, 1st is trashed by bootsec\r
	53	DL_DISKTAB = 44\r
	54	\r
	55	; We support disk label version 3 "3Vld" in our little endian world\r
	56	DL_V3 = 33566c64h\r
	57	\r
	58	; NeXT disktab\r
	59	DT_SECSIZE = 48\r
	60	DT_BOOT0_BLKNO = 80\r
	61	\r\r
	62	; This code is a replacement for boot1. It is loaded at 0x0:0x7c00\r
	63	\r
	64	start:\r
65	mov ax,BOOTSEG
66	cli ; interrupts off\r
67	mov ss,ax ; set up stack seg\r
68	mov sp,0fff0h\r
69	sti ; reenable interrupts\r
70
71	xor ax,ax
72	mov es,ax
73	mov ds,ax
74	mov si,7C00h
75	cld ; so pointers will get updated\r
76	mov di,0E000h ; relocate boot program to 0xE000\r
77	mov cx,100h ; copy 256x2 bytes\r
78	repnz movsw ; move it\r
79	off1 = 0E000h + (a1 - start)\r
80	jmp FAR 0000:off1 ; jump to a1 in relocated place\r
81
82	a1:\r
83	mov ax,0E00h\r
84	mov ds,ax\r
85	mov ax,BOOTSEG\r
86	mov es,ax\r
87	\r
88	; load the boot loader (boot2) into BOOTSEG:BUFSZ\r
89	call loadboot\r
90	\r
91	; ljmp to the second stage boot loader (boot2).\r
92	; After ljmp, cs is BOOTSEG and boot1 (BUFSZ bytes) will be used\r
93	; as an internal buffer "intbuf".\r
94	\r
95	xor edx,edx ; bootdev = 0 for hard disk\r
96	IF ( BOOTDEV EQ FLOPPY )
97	inc edx ; bootdev = 1 for floppy disk
98	ENDIF
99
100	;boot2 immediately follows disk buffer; 4K + BUFSZ\r
101	jmp FAR BOOTSEG:(BOOTOFF + BUFSZ)
102	; jump to boot2 in loaded location\r
103	\r
104	\r
105	\r
106	loadboot:\r
107	mov si, OFFSET intro\r
108	call message ; display intro message\r
109	\r
110	; load second stage boot from fixed disk\r
111	; get boot drive parameters\r
112	; Note: I believe that the bootsector read may not be necessary;\r
113	; at least some blk0 bootsectors leave a pointer to the active\r
114	; partition entry in si (assuming there was another blk0 bootsec)\r
115	\r
116	call getinfo\r
117	\r
118	IF ( BOOTDEV EQ HDISK )
119
120	; read sector 0 into BOOTSEG:0 by using BIOS call (INT 13H 02H)\r
121	; this gets info on the disk's actual partition table\r
122	; However, in the case of multiple partitions, this may not\r
123	; be the same as the sector with the code here.\r
124	\r
125	mov di,5 ; try 5 times to read bootsector\r
126	\r
127	retry_disk:\r
128	xor bx, bx ; buffer is BOOTSEG:0\r
129	mov ax,201h\r
130	mov cx,bx\r
131	mov dx,bx\r
132	mov bx,BOOTOFF ; actually, it's 0:BOOTOFF
133	inc cx ; cyl 0, sector 1\r
134	mov dl,BOOTDEV ; target 0, head 0\r
135	\r
136	push di\r
137	int 13h ; read the bootsector\r
138	pop di\r
139	\r
140	jnb read_success1\r
141	\r
142	; woops, bios failed to read sector\r
143	xor ax,ax\r
144	int 13h ; reset disk\r
145	dec di\r
146	jne retry_disk\r
147	\r
148	jmp read_error ; disk failed\r
149	\r
150	\r
151	read_success1: ; find the NeXT partition\r
152	mov bx,PARTSTART\r
153	mov cx,NUMPART\r
154	\r
155	again:\r
156	mov al, [es:(bx+BOOTOFF)+NAME_OFFSET]
157	; get partition name\r
158	cmp al, NEXTNAME ; is it NeXT partition?\r
159	jne cont ; nope, keep looking\r
160	\r
161	foundNextPart: ; found it, get label location\r
162	\r
163	mov eax, [es:(bx+BOOTOFF)+PARTSEC]
164	; offset to NeXT partition\r
165	add eax, DISKLABEL ; add offset to the label\r
166	jmp getLabl ; fetch that label\r
167	\r
168	cont:\r
169	add bx, PARTSZ\r
170	loop again ; if more part table entries,
171	; keep looking\r
172	\r
173	; fall through, didn't find NeXT disk partition entry\r
174	\r
175	no_fdisk:\r
176	ENDIF
177	; Read NeXT disk label\r
178	mov eax, DISKLABEL ; Get block number of label\r
179	getLabl:\r
180	mov bx,BOOTOFF ; read into load area
181	mov cx,1
182	call readSectors\r
183	\r
184	; we used to think about testing the disk label version here...\r
185
186	mov bx,BOOTOFF ; point to beginning of label
187	\r
188	; Use values from label to read entire boot program\r
189	; Get block number of boot\r
190	; Get dl_secsize and dl_boot0_blkno[0]\r
191	mov edx, [es:(bx + DL_DISKTAB+DT_SECSIZE)]\r
192	bswap edx ; edx -> sector size\r
193	\r
194	mov eax, [es:(bx + DL_DISKTAB+DT_BOOT0_BLKNO)]\r
195	bswap eax ; eax -> block #\r
196
197	; Compute dl_secsize * dt_boot0_blkno[0] / 512\r
198	shr edx, 9 ; divide dl_secsize by 512\r
199	mul edx ; multiply boot block loc
200	; by dl_secsize/512\r
201	; eax has secno\r
202	mov bx, (BUFSZ + BOOTOFF) ; read boot2 into BOOTSEG:BUFSZ\r
203	mov edi, LOADSZ ; read this many sectors\r
204	nexsec:\r
205	push eax ; push sector #\r
206	push bx ; push buffer address\r
207	mov ecx, edi ; max number of sectors to read
208
209	call readSectors\r
210	pop bx\r
211	pop eax\r
212	add eax, ecx ; add number of sectors read
213	sub di, cx
214	shl cx, 9 ; multiply by 512 bytes per sector
215	add bx, cx
216
217	cmp di, 0
218	jne nexsec\r
219
220	ret\r
221	\r
222	spt: DW 0 ; sectors;track (one-based)\r
223	spc: DW 0 ; tracks;cylinder (zero-based)\r
224	nsec: DW 0 ; number of sectors to read
225	\r
226	readSectors: ; eax has starting block #, bx has offset from BOOTSEG\r
227	; cx has maximum number of sectors to read
228	; Trashes ax, bx, cx, dx\r
229	\r
230	; BIOS call "INT 0x13 Function 0x2" to read sectors\r
231	; ah = 0x2 al = number of sectors\r
232	; ch = cylinder cl = sector\r
233	; dh = head dl = drive (0x80=hard disk, 0=floppy disk)\r
234	; es:bx = segment:offset of buffer\r
235
236	IF ( BOOTDEV EQ FLOPPY )
237	push eax\r
238	mov al,'.'\r
239	call putchr\r
240	pop eax\r
241	ENDIF\r
242	\r
243	push bx ; save offset\r
244	mov [WORD nsec], cx
245	\r
246	mov ebx, eax ; bx -> block #\r
247	xor ecx, ecx\r
248	mov cx, [WORD spc] ; cx -> sectors/cyl\r
249	\r
250	xor edx,edx ; prepare for division\r
251	div ecx ; eax = cyl, edx=remainder\r
252	push ax ; save cylinder #, sec/spc\r
253	\r
254	mov eax, edx\r
255	mov cx, [WORD spt] ; ecx -> sectors/track\r
256	xor edx,edx ; prepare for division\r
257	div ecx ; eax = head\r
258	push ax ; save head, (secspc)/spt\r
259	\r
260	mov eax, ebx ; reload block #\r
261	xor edx, edx ; prepare for division\r
262	div ecx ; edx has sector #\r
263	\r
264	sub cx, dx ;cx now has number of sectors to read
265	cmp cx, [WORD nsec]
266	jge last ; use the minimum of bx and cx
267	mov [WORD nsec], cx
268	last:
269
270	mov cx, dx ; cl -> sector\r
271	inc cl ; starts @ 1\r
272	pop ax ; get head\r
273	mov dh, al ; dh -> head\r
274	\r
275	pop ax ; get cyl\r
276	mov ch, al ; ch -> cyl\r
277	mov dl, BOOTDEV ; floppy disk\r
278	\r
279	xor al,al\r
280	shr ax,2\r
281	or cl,al ; retain pesky big cyl bits\r
282
283	; mov al, 1 ; get # of sectors\r
284	;pop ax ; number of sectors to read
285	mov ax, [WORD nsec]
286	pop bx ; get buffer\r
287	mov ah, 2 ; bios read function\r
288	\r
289	int 13h\r
290	\r
291	jb read_error\r
292	mov cx, [WORD nsec] ; return number of sectors read
293	ret\r
294	\r
295	\r
296	getinfo: ; get some drive parameters\r
297	mov dl, BOOTDEV ; boot drive is drive C\r
298	mov ah, 8h\r
299	push es
300	int 13h\r
301	pop es
302	\r
303	mov al, dh ; max head #\r
304	inc al ; al -> tracks/cyl\r
305	and cx, 3fh ; cl -> secs/track\r
306	mul cl ; ax -> secs/cyl\r
307	mov [WORD spc], ax\r
308	mov [WORD spt], cx\r
309	\r
310	ret\r
311	\r
312	\r
313	message: ; write the error message in ds:esi
314	; to console\r
315	push es\r
316	mov ax,ds\r
317	mov es,ax\r
318	\r
319	mov bx, 1 ; bh=0, bl=1 (blue)\r
320	cld\r
321	\r
322	nextb:\r
323	lodsb ; load a byte into al\r
324	cmp al, 0\r
325	je done\r
326	mov ah, 0eh ; bios int 10, function 0xe\r
327	int 10h ; bios display a byte in tty mode\r
328	jmp nextb\r
329	done: pop es\r
330	ret\r
331	\r
332	putchr:\r
333	push bx\r
334	mov bx, 1 ; bh=0, bl=1 (blue)\r
335	mov ah, 0eh ; bios int 10, function 0xe\r
336	int 10h ; bios display a byte in tty mode\r
337	pop bx\r
338	ret\r
339
340	IF SDEBUG\r
341	hexout:\r ; print ebx as hex number
342	push cx\r
343	push ax\r
344	mov cx,8 ;output 8 nibbles\r
345	\r
346	htop:\r
347	rol ebx,4\r
348	mov al,bl\r
349	and al,0fh\r
350	cmp al,0ah\r
351	jb o_digit\r
352	add al,'A'-10\r
353	jmp o_print\r
354	o_digit: add al,'0'\r
355	o_print: call putchr\r
356	dec cx\r
357	jne htop\r
358	; mov al,10\r
359	; call putchr\r
360	; mov al,13\r
361	; call putchr\r
362	mov al,' '
363	call putchr
364	pop ax\r
365	pop cx\r
366	ret\r
367	ENDIF\r
368	\r
369	\r
370	read_error:\r
371	mov si, OFFSET eread\r
372	boot_exit: ; boot_exit: write error message and halt\r
373	call message ; display error message\r
374	halt: jmp halt\r
375	\r
376	\r
377	intro: db 10,'NEXTSTEP boot1 vXX.XX.XX.XX.XX',10,13,0\r
378	eread: db 'Read error',10,13,0\r
379
380	; the last 2 bytes in the sector contain the signature\r
381	d1:\r
382	a2 = 510 - (d1 - start)\r
383	DB a2 dup (0)\r
384	DW 0AA55h\r
385	ENDS\r
386	END\r