v2.0/source/SYSINIT.txt

   1     SYSINIT is  a module linked behind the OEM bios.  It takes
   2 over  the  system  initialization  after  the  OEM  bios   has
   3 performed any  initialization  it  needs  to  do.   Control is
   4 transfered with a long jump to the external  variable  SYSINIT
   5
   6
   7     The OEM  has  the  following  variables declared external:
   8
   9     CURRENT_DOS_LOCATION    WORD
  10
  11 This word  contains  the  segment  number of the DOS before it
  12 is relocated.  The OEM bios must set this value.
  13
  14     FINAL_DOS_LOCATION      WORD
  15
  16 This word contains the segment number of the DOS after SYSINIT
  17 moves it.  The OEM bios must set this value.
  18
  19     DEVICE_LIST             DWORD
  20
  21 This  double  word  pointer  points  to  the  linked  list  of
  22 character and block device drivers.  The  OEM  must  set  this
  23 value.
  24
  25     MEMORY_SIZE             WORD
  26
  27 This word  contains  the  number  of  RAM  paragraphs.  If the
  28 bios doesn't set  this  variable  SYSINIT  will  automatically
  29 calculate it.   NOTE:  systems with PARITY checked memory must
  30 size memory in the BIOS.  SYSINITs method is to  write  memory
  31 and read it back until it gets a mismatch.
  32
  33     DEFAULT_DRIVE           BYTE
  34
  35 This is  the initial default drive when the system first comes
  36 up.  drive a=0, drive b=1,  etc.   If  the  bios  doesn't  set
  37 it then drive a is assumed.
  38
  39     BUFFERS                 BYTE
  40
  41 This is  the  default  number of buffers for the system.  This
  42 value may be overridden by the user in  the  CONFIG.SYS  file.
  43 It is DBed to 2 in SYSINIT it should be greater than 1.
  44
  45     FILES                   BYTE
  46
  47 This is  the  default  number  of  files for the system.  This
  48 value may be overridden by the user in  the  CONFIG.SYS  file.
  49 It is  DBed  to  8 in SYSINIT, values less than 5 are ignored.
  50
  51     SYSINIT                 FAR
  52
  53 The entry  point  of  the  SYSINIT  module.  OEM BIOS jumps to
  54 this label at the end of its INIT code.
  55
  56     The OEM  has  the  following  variables declared public:
  57
  58     RE_INIT                 FAR
  59
  60 This is an entry point which allows the BIOS to do some INIT
  61 work  after  the  DOS is initialized.  ALL REGISTERS MUST BE
  62 PRESERVED.  On entry DS points to the first available memory
  63 (after  the DOS).  DS:0 points to a 100H byte program header
  64 prefix which represents  the  "program"  currently  running.
  65 This  program  should  be  thought  of  as  the OEM BIOS and
  66 SYSINIT taken together.  This is not  a  normal  program  in
  67 that  no  memory  is  allocated to it, it is running in free
  68 memory.
  69 NOTES:
  70      At the time this routine is called SYSINIT occupies the
  71 highest 10K of memory ("highest" is determined by the  value
  72 of the MEMORY_SIZE variable), DO NOT DO WRITES THERE.
  73      Since this is called AFTER DOS is initialized, you can
  74 make system calls.  This also implies that the code for this
  75 routine    CANNOT   be   thrown   away   by   use   of   the
  76 FINAL_DOS_LOCATION since the DOS has already been moved.
  77      If you don't want  anything done just set this to point
  78 at a FAR RET instruction.
  79