User`s guide

60 DC 900-1516D

ICP2432 User’s Guide for OpenVMS Alpha (DLITE Interface)

transfers include at least a protocol header, each buffer read from the ICP contains at

least the size of that header.

4.1.2.4 Node Numbers (P4)

Once a channel is assigned to the ICP device name, data is directed to individual ports

(links) on that ICP through the use of a node number in the P4 parameter of the QIO

call. A node number represents a logical full-duplex path to the protocol software on the

ICP. The legal values for node numbers in the ICP driver are 1 to 126. Note that this

range of numbers starts over again for each ICP device name. For example, node 1 on

ZJA0 is different from node 1 on ZJB0. The P4 parameter is a 32-bit word that contains

the read node number in the low byte and the write node number in the next byte, as

shown in Figure4–1. As a general rule, application programs should place the desired

node number in both low bytes of the parameter (for example, 0101 hex, 0202 hex, and

so on) for all QIO transfers, read or write. The device driver uses the appropriate byte

and ignores the other.

Note

Read and write node numbers should not be confused with

PCIbus node numbers.

The protocol software on the ICP determines how the device driver node numbers are

used. Most of Protogate’s current protocol software uses node numbers to form “ses-

sion” connections through the device driver. Using this method, all writes to the ICP

use nodes 1 and 2. All reads from the ICP use nodes 3 to 126. Some Protogate protocols

Figure 4–1: P4 Parameter Format

031

read node numberunused unused write node number

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