HP Vectra Technical Reference Manual page 276

RESETJROCESSOR:
CALL FAR PTR OFFFFH:OH
,. Reboot system.
; This time with
1
KB morE:
; memory allocated
to
the
,. EX-BIOS data area
I
OK:
MOV
MOV
INT
BP, V_SYSTEM
AH , F_RAM__RET
HP_ENTRY
,. Set new "Iast used OS"
,. and "Max OS"
; Memory is allocated
9.1.3.2 HP_VECTOLTABLE Manipulation
All drivers in the EX-BIOS code module are accessed through the HP_VECTOLTABLE.
The V_SYSTEM driver provides a set of functions which allows the entries in the
HP_VECTOLTABLE to be set and/or modified. There are nine functions, which represent the
permutations of three parameters.
The first parameter determines whether a vector is to be inserted or exchanged with values
passed in the 80286 registers. Vectors are typically inserted into the HP_VECTOLTABLE during
the boot process, whereas vector exchanges are used to implement driver mapping. For example,
the V_QWERTY keyboard translator driver is installed in the HP_VECTOLTABLE during the
boot process. If keyboard scancodes from the QWERTY keypad were to be mapped to a Dvorak
translator, the IP, CS, and DS of the Dvorak translator driver would be exchanged with the
existing vector (so the vector could be restored to its original value at a later time).
The second parameter is the vector type. The HP_VECTOLTABLE has three types of vectors;
fixed, reserved, and free;_ 'Fixed vectors are those assigned to the default EX-BIOS drivers. The first
51 vectors in the HP_VECTOLTABLE are fixed. Reserved vectors are set aside for future
expansion. There are 24 reserved vectors, which are located at vector addresses 138H through
1C8H inclusive. Free vectors are provided to allow user-supplied drivers to be added to the
system.
The final parameter involves the Data Segment (DS) of the driver. Drivers may allocate their data
areas from the EX-BIOS data area as explained above, they may provide their own, or use the
global data area of the EX-BIOS. The EX-BIOS drivers all use the DS allocation functions, while an
external driver (for example, one installed as an MS-DOS device driver) may supply their own data
area external to the EX-BIOS data area. Drivers supplying their own DS must pass it as a
parameter to V_SYSTEM when the driver has completed initialization.
System Drivers 267