Determining and Selecting Input and Output (I/O) Paths

The system identifies adapter interfaces to a system bus and the associated devices by an I/O path. The I/O path is the address of the interface hardware and the physical path to reach a device.

When the system is reset or the power is turned on, hardware routines read and initialize the I/O paths needed to boot the system. These boot paths consist of the primary boot path, for booting from disk-resident software; the alternate boot path, for booting from a system load tape; and the console boot path, for locating console operator intervention.

Boot paths for the primary boot device, the alternate boot device, and the console are shown as numbers separated by periods.

Series 922 through Series 949 boot paths

Each I/O path is constructed "top down" from where the device is physically attached to the system. The Series 922 through Series 949 I/O path is determined by the channel adapter (CA) module number, the device adapter (DA) slot number, and the device address:

   CA Module Number.DA Slot Number.Device Address

The CA module number specifies the number of card slots in the central bus (CTB) that the channel adapter is attached to, multiplied by four. The Series 922 through Series 932 CA modules are assigned a numerical value of 4 or 8. The Series 935 CA module is assigned a numerical value of 4 or 36. The Series 949 CA module is assigned a numerical value of 8 or 40.

DA slot numbers range from 0 to 13. Slots 0 through 7 are recommended for use.

The address of the device itself depends on the adapter. In addition, data communication devices may have an additional logical or virtual device number in the I/O path specification.

For example, in figure 2-3 the CA module number is 4, the HP-IB channel CIB interface slot is 5, and the magnetic tape device address is 0. This establishes an I/O path for the tape drive as 4.5.0.0.0.0.0.0. Trailing zeros (those occurring after the third digit) are intended for future use.

Figure 2-3 Series 922 through Series 935 I/O Device Paths

Series 950 through Series 980 boot paths

On Series 950 through Series 980 systems, I/O path construction begins with the bus converter (BUS CONV), which connects the system's main bus (SMB) and central bus (CTB). The channel adapter connects the central bus and the channel I/O bus (CIB). The logical construction concludes with the device adapter, which connects the I/O device to the CIB. An I/O device connects to a device adapter card through an interface cable.

A Series 950 through Series 980 I/O path is specified as follows:

   BUS CONV/CA Module Number.DA Slot Number.Device Address

The bus converter specifies the number, either 2 or 6, of the interface slot that contains the adapter boards for the SMB and the central bus.

The CA module number specifies the number of the interface slot that contains the adapter boards for the central bus and the CIB. The CA module number is assigned a numerical value of 4, 8, 16, 20, or 24.

DA CIO section slot numbers range from 0 to 4.

The address of the device itself depends on the adapter. In addition, data communication devices may have an additional logical or virtual device number in the I/O path specification.

In figure 2-4, for example, the bus converter is 6, the CA module number is 4, the HP-IB channel CIB interface slot is 3, and the magnetic tape device address is 3. This establishes an I/O path for the tape drive as 6/4.3.3.0.0.0.

Figure 2-4 Series 950 through Series 980 I/O Device Paths

There are several ways to determine the I/O path for devices that are attached to the system:

Refer to figures 2-3 and 2-4 for address and physical connection information.
Generate a list of paths for devices that have already been configured by using the LPATH command of the SYSGEN utility IO Configurator. SYSGEN does not tell you if the configured device is active or available. During the system boot (using the ISL START command), information on which paths have been configured and which devices are available or not available is listed as the "System State at Boot Time." (For more information on the system state, refer to Chapter 3 “System Startup Functions” and Appendix B “Startup, Dump, and Shutdown Listings”. For more information on SYSGEN, refer to Chapter 4 “Using the System Generator (SYSGEN)”.)
Use the ISL utility, IOMAP, to list the devices on the system. (For more information on IOMAP, refer to Appendix E “Verifying Attached Devices”.) For 9X8LX and 9X8RX systems, use the ODE utility to list devices on the system.

Determining and Selecting Input and Output (I/O) Paths

Technical documentation

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Series 922 through Series 949 boot paths

Series 950 through Series 980 boot paths