Because I/O interfaces are often platform-dependent, several chapters in this manual have separate sections for managing an I/O device on different operating system platforms.

This chapter introduces topics related to managing I/O devices in Caché. It includes the following topics:

Caché supports both physical and logical I/O devices. The supported physical devices include:

The supported logical devices include:

There are several Caché utilities to manage devices. The table below summarizes these utilities and alternative ways of accessing them.

When you install Caché, default devices are defined. These are displayed in the Devices configuration subsection of the Management Portal. Select [Home] > [Configuration] > [Device Settings] > [Devices]. View the list of defined devices.

Caché ships with many default device subtypes. Each device subtype defines device characteristics, such as screen length and form-feed characteristics.

The complete list of subtypes is in the Device Subtypes configuration option of the Management Portal. Select [Home] > [Configuration] > [Device Settings] > [SubTypes]. View the list of defined sub types.

Caché also ships with some magnetic tape devices defined. The complete list of magnetic tape devices is in the Magnetic Tapes Devices configuration option of the Management Portal. Select [Home] > [Configuration] > [Device Settings] > [MagTapes]. View the list of defined magnetic tape devices. Magnetic tape devices can be assigned device numbers 47 through 62; by default, magnetic tape devices are assigned to device numbers 47, 48, 57, and 58. (The magnetic tape devices are also listed in the Devices option.)

When you define a device in the Devices configuration section of the Management Portal, you provide three device identifiers to specify a device:

These device identifiers have several advantages over physical device names:

For more information about using device identifiers, see the Accessing Devices section.

You can associate one or more mnemonics with a particular Device. You use a mnemonic in response to the “Device:” prompt issued by the %IS character-based utility.

Mnemonics provide these advantages:

You can identify devices by a number or by their operating system name. You use this identifier in OPEN commands.

You can define one or more alias values for each Caché device you define. When a user specifies an alias in an OPEN command, Caché translates it into the Device ID.

The default Device IDs that Caché provides are appropriate for most users. However, some users may want to override these defaults, particularly for magnetic tape devices. You can do this by providing an alias as part of the device's configuration settings in the Management Portal.

When you install Caché, these are the default device numbers and mnemonics for each type of device.

However, Caché also recognizes other device numbers that you can use to define devices. The following table lists the recognized default device numbers.

In addition to the mnemonics and device numbers, Caché supports I/O device types. Each internal device number belongs to one of these types. The following table shows the device types:

You define, edit, and delete devices in the Devices configuration settings of the Management Portal. The information you enter is stored in the ^%IS global. For more information about this global, see the section Structure of ^%IS Global.

If you make device changes while Caché is running, you are prompted as to whether you want to activate the changes without restarting Caché. If you agree to activate the changes, the new definitions are made available immediately to users.

Caché supports up to sixteen tape drives on each CPU. Any tape drive that your system supports can be used with Caché.

Before you can use a magnetic tape device with Caché, you must define it in the MagTape configuration settings of the Management Portal. Take the following steps:

You should delete outmoded magnetic tape device definitions so that your users do not inadvertently select them.

Many magnetic tape utilities (including %GIF, %GOF, %RIMF, and %ROMF) ask you whether to wait 15 seconds if the utility is not able to open the magnetic tape or cartridge tape device. If you answer “Yes” or do not respond within 10 seconds, the utility lets you decide whether to continue waiting. If you choose not to wait, the system stops trying to open the device.

On a Caché for Windows system, you must use device numbers for magnetic tape devices, interjob communication devices, and routine interlock devices. For terminals and printers, you can use device mnemonics or device numbers you assign.

On a Caché for UNIX® system, you can use UNIX® file specifications to refer to files or you can set up device numbers to refer to files.

You can access a device in one of two ways:

If you want users of a character-based application to select a device interactively, call the %IS utility from the application. You can learn more about the %IS utility in the section Allowing Users to Specify a Device.

To select a device using the %IS utility:

You can use an OPEN command either at the Caché programmer prompt or within an ObjectScript application to open a specific device for reading and writing. When you specify the device, you can use its Device ID or its alias.

Device identifiers you use with %IS or an OPEN command go through up to three levels of interpretation. Thus, if you enter the mnemonic 47 at the %IS global “Device:” prompt, the final device ID that is used may be different. The three levels are described below.

The first level is used if a device is selected with the %IS utility. Mnemonics in the ^%IS global can be associated with device numbers. The %IS utility then issues an OPEN command to that device number.

In an OPEN command, Caché checks to see if this number exists in the Alias column of the Device panel table. If so, it translates it to the actual device number or name for that device.

If the device number is of class Mag Tape, the system checks the MagTape configuration settings of the Management Portal to see which physical tape drive device to access.

Programmers can control devices by using WRITE /mnemonic commands in their applications. For instance, programmers can move the cursor to a specific column in the current line on a terminal device when they use the %X364 mnemonic space with this command:

  WRITE /CHA(column)

The action caused by any particular value of mnemonic is determined by the mnemonic space the WRITE command is using. A mnemonic space is a routine with entry points (mnemonics) that define device actions and attributes.

The WRITE command uses the mnemonic space defined in the OPEN or USE command for the device. If the OPEN or USE command includes no mnemonic space argument, then Caché uses the default mnemonic space for the device type.

For further details on mnemonic spaces, see the.

Caché ships with two predefined (default) mnemonic spaces, described in the following table:

The predefined mnemonic spaces are the default mnemonic spaces for:

These defaults are defined in the Management Portal. Select [Home] > [Configuration] > [Device Settings] > [IO Settings].

If you create your own mnemonic space routine(s), you may want to change the default mnemonic spaces Caché uses for one or more of the four device types.