usr/src/sys/i386/stand/fdbootblk.c

/*-
 * Copyright (c) 1990 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 7.2 (Berkeley) 5/4/91
 */

/*
 * fdbootblk.s:
 *      Written 10/6/90 by William F. Jolitz
 *      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.
 */
/*#include "/sys/i386/isa/isa.h"
#include "/sys/i386/isa/fdreg.h"*/
#define NOP     jmp 1f ; nop ; 1:
#define BIOSRELOC       0x7c00
#define start   0x70400

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

        .byte 0xfa,0xb8,0x30,0x00,0x8e,0xd0,0xbc,0x00,0x01 #ll fb

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

        /* step 1 load new descriptor table */

        .byte 0x2E,0x0F,1,0x16
        .word   BIOSRELOC+0x4a  #GDTptr
        # word aword cs lgdt GDTptr

        /* step 2 turn on protected mode */

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

        /* step 3  reload segment descriptors */

 1:
        xorl    %eax,%eax
        movb    $0x10,%al
        movl    %ax,%ds
        movl    %ax,%es
        movl    %ax,%ss
        word
        ljmp    $0x8,$ BIOSRELOC+0x59   /* would be nice if .-RELOC+0x7c00 worked */

 /* 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:
NullDesc:       .word   0,0,0,0 # null descriptor - not used
CodeDesc:       .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)
DataDesc:       .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  # GDT -- arrgh, gas again!
readcmd: .byte 0xe6,0,0,0,0,2,18,0x1b,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 */