HP Vectra Technical Reference Manual page 438

This feature of the EX-BIOS system can also be utilized by application programs and system
software. Any program needing a limited amount of RAM outside the operating system domain
can obtain this from the EX-BIOS system.
The functions F_RAM_GET and F_RAM_RET in the V_SYSTEM driver can be used to
manipulate the EX-BIOS free memory. The driver can also use the installation functions
F _INS_FREEGETDS or F_INS_FIXGETDS to obtain free memory. See Section 9 for more details
of these functions.
G.4.3 Getting a Free Vector
In order for an application to access an EX-BIOS driver it must call the driver through the
HP_VECTOLTABLE. Thus, each driver must request a free vector from this table.
To get a free vector from the HP_VECTOLTABLE, a driver can use the function
F _INS-YCHGFREE, F_INS_FREEOWNDS, F_INS_FREEGETDS or F_INS_FREEGLBDS in the
V_SYSTEM driver. Each of these functions installs the driver at the next available free vector.
Once the driver has a vector address installed in the table, an application can call the driver by
loading BP with the vector address of the driver and doing an HP_ENTRY interrupt (6FH).
G.5 EX-BIOS Driver Functions
EX-BIOS drivers support a standard set of functions and subfunctions. Nine standard function
codes are defined, and several of these functions have subfunctions defined within them. These
functions and subfunctions are summarized in table G.2. A detailed description of each defined
function and subfunction follows.
If a driver receives a function it does not implement, it must return a status code of
RS_UNSUPPORTED (02H) in the AH register. This lets the application know that the driver has
not handled this function, but that it can continue if it is appropriate. This protocol frees the
driver from having to implement all the defined functions and allows applications to call drivers
in a consistent way.
If a driver receives a function code that it does not implement, it may also
II
delegate" the
function to another driver. A driver may be written so that it calls another driver when it receives
an unimplemented function or subfunction request.
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