79 lines
3.0 KiB
Plaintext
79 lines
3.0 KiB
Plaintext
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SYSINIT is a module linked behind the OEM bios. It takes
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over the system initialization after the OEM bios has
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performed any initialization it needs to do. Control is
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transfered with a long jump to the external variable SYSINIT
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The OEM has the following variables declared external:
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CURRENT_DOS_LOCATION WORD
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This word contains the segment number of the DOS before it
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is relocated. The OEM bios must set this value.
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FINAL_DOS_LOCATION WORD
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This word contains the segment number of the DOS after SYSINIT
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moves it. The OEM bios must set this value.
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DEVICE_LIST DWORD
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This double word pointer points to the linked list of
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character and block device drivers. The OEM must set this
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value.
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MEMORY_SIZE WORD
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This word contains the number of RAM paragraphs. If the
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bios doesn't set this variable SYSINIT will automatically
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calculate it. NOTE: systems with PARITY checked memory must
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size memory in the BIOS. SYSINITs method is to write memory
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and read it back until it gets a mismatch.
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DEFAULT_DRIVE BYTE
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This is the initial default drive when the system first comes
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up. drive a=0, drive b=1, etc. If the bios doesn't set
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it then drive a is assumed.
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BUFFERS BYTE
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This is the default number of buffers for the system. This
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value may be overridden by the user in the CONFIG.SYS file.
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It is DBed to 2 in SYSINIT it should be greater than 1.
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FILES BYTE
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This is the default number of files for the system. This
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value may be overridden by the user in the CONFIG.SYS file.
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It is DBed to 8 in SYSINIT, values less than 5 are ignored.
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SYSINIT FAR
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The entry point of the SYSINIT module. OEM BIOS jumps to
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this label at the end of its INIT code.
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The OEM has the following variables declared public:
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RE_INIT FAR
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This is an entry point which allows the BIOS to do some INIT
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work after the DOS is initialized. ALL REGISTERS MUST BE
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PRESERVED. On entry DS points to the first available memory
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(after the DOS). DS:0 points to a 100H byte program header
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prefix which represents the "program" currently running.
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This program should be thought of as the OEM BIOS and
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SYSINIT taken together. This is not a normal program in
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that no memory is allocated to it, it is running in free
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memory.
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NOTES:
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At the time this routine is called SYSINIT occupies the
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highest 10K of memory ("highest" is determined by the value
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of the MEMORY_SIZE variable), DO NOT DO WRITES THERE.
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Since this is called AFTER DOS is initialized, you can
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make system calls. This also implies that the code for this
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routine CANNOT be thrown away by use of the
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FINAL_DOS_LOCATION since the DOS has already been moved.
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If you don't want anything done just set this to point
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at a FAR RET instruction.
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