Specifications

System Macros Invoked by Drivers

DDTAB

[cloneducb=+IOC$RETURN]

Address of routine called when a UCB is cloned by the $ASSIGN system service.

Description

The DDTAB macro creates a driver dispatch table (DDT). The table has a label

of devnam$DDT. Just preceding the table, DDTAB generates the driver code

program section with the following statement:

.PSECT $$$115_DRIVER

The DDTAB macro writes the address of the universal executive routine vector

IOC$RETURN into routine address ﬁelds of the DDT that are not supplied in the

macro invocation (with the exception of the mntver argument). IOC$RETURN

simply executes an RSB instruction.

A plus sign (+) precedes the address of any speciﬁed routine that is part of the

operating system: that is, it is an address that is not relative to the location of

the driver. No plus sign precedes the address of a routine (such as a start-I/O

routine) that is part of the driver module.

Example

DDTAB - ;DDT-creation macro

DEVNAM=XX, - ;Name of device

START=XX_START,- ;Start-I/O routine

FUNCTB=XX_FUNCTABLE,- ;FDT address

CANCEL=+IOC$CANCELIO,- ;Cancel-I/O routine

REGDMP=XX_REGDUMP,- ;Register-dumping routine

DIAGBF=<<15*4>+<<3+5+1>*4>>,- ;Diagnostic buffer size

ERLGBF=<<15*4>+<1*4>+<EMB$L_DV_REGSAV>> ;Error message buffer size

This code excerpt uses the DDTAB macro to create a driver dispatch table for the

XX device type. Note that because the cancel-I/O routine is part of the operating

system, its address is preceded by a plus sign (+).

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