Specifications

System Macros Invoked by Drivers

FUNCTAB

Creates a driver’s function decision table (FDT) and generates FDT entries.

Format

FUNCTAB [action] ,codes

Parameters

[action]

Address of an FDT routine that the operating system calls when preprocessing

an I/O request whose function code matches a function indicated in the codes

argument. A plus sign (+) precedes the address of any speciﬁed FDT routine

that is part of the operating system. No plus sign precedes the address of an FDT

routine that is contained within the driver module.

You cannot specify an action argument in a driver’s ﬁrst two invocations of the

FUNCTAB macro.

codes

List of I/O function codes that system preprocessing services by calling the FDT

routine speciﬁed in the action argument of the FUNCTAB macro invocation.

The macro expansion preﬁxes each code with the string IO$_; for example,

READVBLK expands to IO$_READVBLK.

Description

A device driver uses several invocations of the FUNCTAB macro to generate the

three components of a function decision table:

• The list of valid I/O function codes

• The list of buffered I/O function codes

• One or more FDT entries

The ﬁrst two invocations of the FUNCTAB macro in a driver generate the lists

of valid I/O functions and buffered I/O functions, respectively. These invocations

include the codes argument, but not the action argument. If no buffered I/O

functions are deﬁned for the device, the codes argument to the second invocation

of the FUNCTAB macro speciﬁes an empty list.

Each succeeding invocation of the FUNCTAB macro generates an FDT entry.

Each FDT entry speciﬁes all or a subset of the valid I/O function codes and the

address of an FDT routine that performs I/O preprocessing for those function

codes. You can specify any valid I/O function code in more than one of these

FUNCTAB macro invocations, thus causing more than one FDT routine to be

called for a single valid I/O function code.

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