/*      $OpenBSD: mbr.S,v 1.3 2022/12/08 02:11:27 guenther Exp $        */
/*      $NetBSD: mbr.S,v 1.1 2006/09/01 21:26:19 uwe Exp $      */

/*-
 * Copyright (c) 2005 NONAKA Kimihiro
 * All rights reserved.
 *
 * 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.
 *
 * 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.
 */

#include <machine/asm.h>

ENTRY(start)
        mova    mbr_end, r0
        mov     r0, r11                 /* r11: relocate address */

        mov.w   mbr_size, r2
        sub     r2, r0
        mov     r0, r10                 /* r10: loaded address */

        mov.w   stack_offset, r1
        add     r1, r0
        mov     r0, r15                 /* r15: stack pointer */

        /* relocate code */
        mova    jmp_start, r0
        mov     r0, r13
        add     r2, r13                 /* calc jump address */

        mov     r10, r0
        mov     r11, r1
1:      mov.b   @r0+, r3
        dt      r2
        mov.b   r3, @r1
        bf/s    1b
         add    #1, r1

        jmp     @r13
         nop

        .align  2
jmp_start:
        /* enable cache */
        mov     #0, r4
        mov     #6, r0
        trapa   #0x3f

        /* print banner */
        mova    banner, r0
        bsr     message
         mov    r0, r4

        /* search bootable partition */
        mov.w   part_offset, r12
        add     r11, r12                /* r12: pointer to partition entry */
        mov     #4, r8                  /* r8: partition loop counter */
loop_part:
        mov.b   @(4, r12), r0
        cmp/eq  #0x00, r0
        bt      next_part

        /* check active partition */
        mov.b   @(0, r12), r0
        cmp/eq  #0x80, r0
        bf      next_part

        /* found bootable partition */
        mov.w   @(8, r12), r0           /* load unaligned 32bit data */
        mov     r0, r1
        mov.w   @(10, r12), r0
        extu.w  r1, r1
        shll16  r0
        or      r1, r0

        mov     r0, r3
        mova    found_sector, r0
        bra     boot_lba
         mov.l  r3, @r0

next_part:
        dt      r8
        bf/s    loop_part
         add    #16, r12

noos_error:
        /* Not found bootable partition */
        mova    ERR_NOOS, r0
error:
        bsr     message
         mov    r0, r4
99:     bra     99b
         nop

read_error:
        bra     error
         mova   ERR_READ, r0

message:
        mov     #32, r0
        trapa   #0x3f
        rts
         nop

read_sector_lba:
        mov     #1, r7
        mov     #2, r0
        trapa   #0x3f
        tst     r0, r0
        bf      read_error
        rts
         nop

boot_lba:
        /* read PBR sector */
        mova    found_sector, r0
        mov     #0x40, r4
        mov.l   @r0, r5
        bsr     read_sector_lba
         mov    r10, r6

        /* flush cache */
        mov     #0, r4
        mov     #6, r0
        trapa   #0x3f

        /* check signature */
        mov.b   @(0, r10), r0
        tst     r0, r0
        bt      noos_error              /* first byte non-zero */
        mov.w   magic_offset, r0
        mov.w   @(r0, r10), r1
        mov.w   magic, r2
        cmp/eq  r1, r2
        bf      noos_error              /* magic */

        /* now jump to PBR */
        mov     r10, r0
        jmp     @r10
         nop


        .align  1
mbr_size:       .word   mbr_end - start
        .align  1
stack_offset:   .word   0x1000
        .align  1
part_offset:    .word   0x1be
        .align  1
magic_offset:   .word   0x1fe

        .align  2
found_sector:   .long   0

        .align  2
banner:         .asciz  "\r\nOpenBSD MBR\r\n"

        .align  2
ERR_INVPART:    .asciz  "No active partition\r\n"
        .align  2
ERR_READ:       .asciz  "Read error\r\n"
        .align  2
ERR_NOOS:       .asciz  "No O/S\r\n"


/* space for mbr_dsn */
        . = start + 0x1b4
        .long   0

/* mbr_bootsel_magic */
        . = start + 0x1b8
        .word   0

/*
 * MBR partition table
 */
        . = start + 0x1be
_pbr_part0:
        .byte   0, 0, 0, 0, 0, 0, 0, 0  
        .byte   0, 0, 0, 0, 0, 0, 0, 0
_pbr_part1:
        .byte   0, 0, 0, 0, 0, 0, 0, 0  
        .byte   0, 0, 0, 0, 0, 0, 0, 0
_pbr_part2:
        .byte   0, 0, 0, 0, 0, 0, 0, 0  
        .byte   0, 0, 0, 0, 0, 0, 0, 0
_pbr_part3:
        .byte   0, 0, 0, 0, 0, 0, 0, 0
        .byte   0, 0, 0, 0, 0, 0, 0, 0

        . = start + 0x1fe
magic:
        .word   0xaa55
mbr_end: