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