Specifications

Writing Device-Driver Tables

4.1 Driver Prologue Table

UCB$B_DEVCLASS Device class

UCB$B_DEVTYPE Device type

UCB$W_DEVBUFSIZ Default buffer size

UCB$Q_DEVDEPEND Device-dependent parameters

• A driver invokes the DPT_STORE macro once, specifying the REINIT

keyword, to automatically generate a driver I/O database reinitialization

routine. This routine, which executes when the driver is ﬁrst loaded into the

system, and whenever the driver is reloaded, initializes those ﬁelds speciﬁed

by the series of DPT_STORE and DPT_STORE_ISR macros that intervene

between the DPT_STORE REINIT and DPT_STORE END declarations.

Drivers use the DPT_STORE macro with the REINIT table marker label to

begin a list of DPT_STORE and DPT_STORE_ISR invocations that supply

initialization and reinitialization data. The following ﬁelds are declared with

the DPT_STORE_ISR macro:

CRB$L_INTD Interrupt service routine

CRB$L_INTD2 Interrupt service routine for second interrupt vector

• A driver invokes the DPT_STORE macro once, specifying the END keyword,

to denote the end of the reinitialization section.

For additional information on how to use the DPTAB, DPT_STORE, and DPT_

STORE_ISR macros, plus an example of their usage, see OpenVMS AXP Device

Support: Reference.

4.2 Driver Dispatch Table

The driver dispatch table (DDT) identiﬁes those driver routines that the operating

system calls to process I/O requests. Every driver must create a DDT.

The routines listed in the DDT can reside in the driver module or in a system

module. Device-dependent routines are normally located in the driver module.

For more information about the system device-independent routines that can be

speciﬁed, see the Systems Routines section of OpenVMS AXP Device Support:

Reference.

The driver creates a DDT by invoking the macro DDTAB. The DDTAB macro

generates a DDT named devnam$DDT, according to the value you supply in

devnam macro argument. It invokes the DRIVER_DATA macro to place the

DDT within the the driver’s data program section ($$$110_DATA).

When the driver is loaded into memory, OpenVMS writes the address of its DDT

into DDB$L_DDT.

You must specify the address of the driver’s function decision table (FDT) in the

functb argument of the DDTAB macro. Several optional arguments allow you to

specify the names of the following routines, if applicable:

• Start-I/O routine

• Controller initialization routine

• Cancel-I/O routine

• Register dumping routine

• Unit initialization routine

• Alternate start-I/O routine

4–3