fdbootblk.c

早期freebsd实现

/*-
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)fdbootblk.c	8.1 (Berkeley) 6/11/93
 */

/*
 * Initial block boot for AT/386 with typical stupid NEC controller.  Works
 * only with 3.5 inch diskettes that have 16 or greater sectors/side.  Goal
 * is to read in sucessive 7.5Kbytes of bootstrap to execute.  No attempt
 * is made to handle disk errors.
 */
#define	NOP		jmp 1f ; nop ; 1:
#define	BIOSRELOC	0x7c00
#define	start		0x70400

/* Gas does not know about 16 bit opcodes... */

	/* step 0 force descriptors to bottom of address space */

	.byte 	0xfa			# cli
	.byte 	0xb8, 0x30, 0x00	# mov $0x0030, %ax
	.byte 	0x8e, 0xd0 		# mov %ax, %ss
	.byte 	0xbc, 0x00, 0x01  	# mov $0x0100, %sp

	xorl	%eax,%eax
	movl	%ax,%ds
	movl	%ax,%es

	/* step 1 load new descriptor table */

	.byte 	0x2e			# seg cs
	.byte 	0x0f, 0x01, 0x16	# lgdt DS:d16
	.word	BIOSRELOC + 0x4a	# [BIOSRELOC + GDTptr]

	/* step 2 turn on protected mode */

	smsw	%ax
	orb	$1,%al
	lmsw	%ax
	jmp	1f
	nop

 1:
	/* step 3  reload segment descriptors */

	xorl	%eax,%eax
	movb	$0x10,%al
	movl	%ax,%ds
	movl	%ax,%es
	movl	%ax,%ss
	word
	ljmp	$0x8, $ BIOSRELOC + 0x59 # [BIOSRELOC + reloc]

 /* 
  * Global Descriptor Table contains three descriptors:
  * 0x00: Null: not used
  * 0x08: Code: code segment starts at 0 and extents for 4 gigabytes
  * 0x10: Data: data segment starts at 0 and extends for 4 gigabytes
  *		(overlays code)
  */
GDT:
NullDsc:.word	0,0,0,0	# null descriptor - not used
CodeDsc:.word	0xFFFF	# limit at maximum: (bits 15:0)
	.byte	0,0,0	# base at 0: (bits 23:0)
	.byte	0x9f	# present/priv level 0/code/conforming/readable
	.byte	0xcf	# page granular/default 32-bit/limit(bits 19:16)
	.byte	0	# base at 0: (bits 31:24)
DataDsc:.word	0xFFFF	# limit at maximum: (bits 15:0)
	.byte	0,0,0	# base at 0: (bits 23:0)
	.byte	0x93	# present/priv level 0/data/expand-up/writeable
	.byte	0xcf	# page granular/default 32-bit/limit(bits 19:16)
	.byte	0	# base at 0: (bits 31:24)

/* 
 * Global Descriptor Table pointer
 *  contains 6-byte pointer information for LGDT
 */
GDTptr:	.word	0x17	# limit to three 8 byte selectors(null,code,data)
	.long 	BIOSRELOC + 0x32	# [BIOSRELOC + GDT]

readcmd: .byte 0xe6, 0x00, 0x00, 0x00, 0x00, 0x02, 18, 0x1b, 0xff

	/* step 4 relocate to final bootstrap address. */
reloc:
	movl	$ BIOSRELOC,%esi
	movl	$ RELOC,%edi
	movl	$512,%ecx
	rep
	movsb
	pushl	$dodisk
	ret

	/* step 5 load remaining 15 sectors off disk */
dodisk:
	movl	$0x70200,%edi
	xorl	%ebx,%ebx
	incb	%bl
	incb	%bl
	movb	$0x20,%al	# do a eoi
	outb	%al,$0x20

	NOP
	movb	$0x07,%al
	outb	%al,$0x21
	NOP
 8:
	movb	%bl,readcmd+4
	movl	%edi,%ecx

	/* Set read/write bytes */
	xorl	%edx,%edx
	movb	$0x0c,%dl	# outb(0xC,0x46); outb(0xB,0x46);
	movb	$0x46,%al
	outb	%al,%dx
	NOP
	decb	%dx
	outb	%al,%dx

	/* Send start address */
	movb	$0x04,%dl	# outb(0x4, addr);
	movb	%cl,%al
	outb	%al,%dx
	NOP
	movb	%ch,%al		# outb(0x4, addr>>8);
	outb	%al,%dx
	NOP
	rorl	$8,%ecx		# outb(0x81, addr>>16);
	movb	%ch,%al
	outb	%al,$0x81
	NOP

	/* Send count */
	movb	$0x05,%dl	# outb(0x5, 0);
	xorl	%eax,%eax
	outb	%al,%dx
	NOP
	movb	$2,%al		# outb(0x5,2);
	outb	%al,%dx
	NOP

	/* set channel 2 */
	# movb	$2,%al		# outb(0x0A,2);
	outb	%al,$0x0A
	NOP

	/* issue read command to fdc */
	movw	$0x3f4,%dx
	movl	$readcmd,%esi
	xorl	%ecx,%ecx
	movb	$9,%cl

 2:	inb	%dx,%al
	NOP
	testb	$0x80,%al
	jz 2b

	incb	%dx
	movl	(%esi),%al
	outb	%al,%dx
	NOP
	incl	%esi
	decb	%dx
	loop	 2b

	/* watch the icu looking for an interrupt signalling completion */
	xorl	%edx,%edx
	movb	$0x20,%dl
 2:	movb	$0xc,%al
	outb	%al,%dx
	NOP
	inb	%dx,%al
	NOP
	andb	$0x7f,%al
	cmpb	$6,%al
	jne	2b
	movb	$0x20,%al	# do a eoi
	outb	%al,%dx
	NOP

	movl	$0x3f4,%edx
	xorl	%ecx,%ecx
	movb	$7,%cl
 2:	inb	%dx,%al
	NOP
	andb	$0xC0,%al
	cmpb	$0xc0,%al
	jne	2b
	incb	%dx
	inb	%dx,%al
	decb	%dx
	loop	2b

	/* extract the status bytes after the read. must we do this? */
	addw	$0x200,%edi	# next addr to load to
	incb	%bl
	cmpb	$16,%bl
	jle	8b
	
	/* for clever bootstrap, dig out boot unit and cylinder */
	pushl	$0
	pushl	$0
	
	/* fd controller is major device 2 */
	pushl	$2	/* dev */

	/* sorry, no flags at this point! */

	pushl $	start
	ret	/* main (dev, unit, off) */

ebootblkcode:

	/* remaining space usable for a disk label */
	
	.space	510-310		/* would be nice if .space 512-2-. worked */
	.word	0xaa55		/* signature -- used by BIOS ROM */

ebootblk: 			/* MUST BE EXACTLY 0x200 BIG FOR SURE */