compilers/linux86-0.16.17/bootblocks/sysboot.s

   1
   2 ! The master boot sector will have setup a stack,
   3 ! this is normally at 0:7c00 down.
   4 ! DS, SS, CS and ES will all have value 0 so the execution address is 0:7c00
   5 ! On entry the register SI will be pointer to the partition entry that
   6 ! this sector was loaded from, DL is the drive.
   7
   8 ! Also if it's a standard Master boot DH will be the head, CX will be the
   9 ! sector and cylinder, BX=7C00, AX=1, DI=7DFE, BP=SI. There's a reasonable
  10 ! chance that this isn't true though.
  11
  12 ! The Master boot itself will have been loaded and run at $07c00
  13 ! The BIOS must have setup a stack because interrupts are enabled
  14 ! Little else can be assumed because DOS doesn`t assume anything either
  15
  16 sysboot_start:
  17 j codestart
  18 nop             ! DOS appears to _require_ this to identify an MSDOS disk!!
  19
  20 .blkb sysboot_start+3-*
  21 public dosfs_stat
  22 dos_sysid:      .ascii "LINUX"  ! System ID
  23                 .byte 0,0,0
  24 dosfs_stat:
  25 dos_sect:       .blkw 1         ! Sector size
  26 dos_clust:      .blkb 1         ! Cluster size
  27 dos_resv:       .blkw 1         ! Res-sector
  28 dos_nfat:       .blkb 1         ! FAT count
  29 dos_nroot:      .blkw 1         ! Root dir entries
  30 dos_maxsect:    .blkw 1         ! Sector count (=0 if large FS)
  31 dos_media:      .blkb 1         ! Media code
  32 dos_fatlen:     .blkw 1         ! FAT length
  33 dos_spt:        .blkw 1         ! Sect/Track
  34 dos_heads:      .blkw 1         ! Heads
  35 dos_hidden:     .blkw 2         ! Hidden sectors
  36
  37 ! Here down is DOS 4+ and probably not needed for floppy boots.
  38
  39 dos4_maxsect:   .blkw 2         ! Large FS sector count
  40 dos4_phy_drive: .blkb 1         ! Phys drive
  41 .blkb 1         ! Reserved
  42 .blkb 1         ! DOS 4
  43
  44 floppy_temp:
  45 dos4_serial:    .blkw 2         ! Serial number
  46 dos4_label:     .blkb 11        ! Disk Label (DOS 4+)
  47 dos4_fattype:   .blkb 8         ! FAT type
  48
  49 !
  50 ! This is where the code will be overlaid, the default is a hang
  51 .blkb sysboot_start+0x3E-*
  52 public codestart
  53 codestart:
  54   j     codestart
  55
  56 ! Partition table
  57 public bootblock_magic
  58
  59 .blkb sysboot_start+0x1BE-*
  60 partition_1:
  61 .blkb 8                 ! IN,SH,SS,ST,OS,EH,ES,ET
  62 .blkw 2                 ! Linear position (0 based)
  63 .blkw 2                 ! Linear length
  64 .blkb sysboot_start+0x1CE-*
  65 partition_2:
  66 .blkb 8                 ! IN,SH,SS,ST,OS,EH,ES,ET
  67 .blkw 2                 ! Linear position (0 based)
  68 .blkw 2                 ! Linear length
  69 .blkb sysboot_start+0x1DE-*
  70 partition_3:
  71 .blkb 8                 ! IN,SH,SS,ST,OS,EH,ES,ET
  72 .blkw 2                 ! Linear position (0 based)
  73 .blkw 2                 ! Linear length
  74 .blkb sysboot_start+0x1EE-*
  75 partition_4:
  76 .blkb 8                 ! IN,SH,SS,ST,OS,EH,ES,ET
  77 .blkw 2                 ! Linear position (0 based)
  78 .blkw 2                 ! Linear length
  79
  80 .blkb sysboot_start+0x1FE-*
  81 bootblock_magic:
  82 .word 0xAA55