HP Vectra Technical Reference Manual page 456

MOV
MOV
MOV
PUSH
INT
POP
BP,
driver's vector address
AH, function code
AL, subfunction code
; i.e. V_SYSTEM (12H)
; any other data passed
" in registers
" Saves app/icat/on's OS
" (6FH)
G.9 Examples of EX-BIOS Drivers
G.9.1 Cursor Pad Scan Code To HP Mouse Driver
The first example driver is called CPP2GID. This driver implements the V_CCPGID EX-BIOS driver.
As such, it translates from cursor control pad keys into graphics input device data.
The driver is installed into the HP_VECTOLTABLE. The SF_INIT subroutine of the driver asks
for enough EX-BIOS RAM to store the driver header and describe record. The DH_V_PARENT
field of the V_CCPGID driver header is initialized to V_LHPMOUSE. The DOS driver portion calls
SF_START of the EX-BIOS driver. SF_START initializes the DH_V_PARENT field of the V_CCP
driver header to V_CCPGID. Then V_LHPMOUSE driver is called with the override function.
The installable driver completes initialization by printing an initialization completed message and
returning back to DOS.
Now when the keyboard driver calls V_CCP to process a cursor control pad key, V_CCP calls
V_CCPGID. The F_ISR of V_CCPGID decodes which key was actually hit. The driver converts
the cursor movement keys (up, down, left, and right) into relative movement data. If the key
pressed was an insert or delete key, it is reported as the left or right button respectively. First the
driver changes the describe record and then reports either a button press or a button release.
After the input data is given to V_LHPMOUSE, the data is available thru the INT 33H STD-BIOS
driver.
Driver Writer's Guide 447