CP6100 I/O Process Programming Manual

Using CP6100: Programming
Some activities of CP6100 are largely transparent to your program
and independent of requests your program makes. These activities
nonetheless contribute to the success of your application. For
example:
• CP6100 runs as a NonStop process pair. If a failure occurs in
the primary processor or its I/O channel, control is switched
to the backup process, which uses the backup processor and I/O
channel. Although the application must normally retry
requests when this happens, it doesn't lose access to the
line, and it doesn't stop running.
• CP6100 communicates with the Communication Subsystem Monitor
(CSM) process, which runs in one of the NonStop processors
to which the subsystem is attached. On behalf of CP6100, the
CSM loads the protocol modules from a disk into the correct
LIUs, either at cold-load time or in response to a system
operator's request. Also, if a controller in a 6100 subsystem
fails, the CSM switches control to the other controller in the
subsystem; the application must recover, but doesn't lose
access to the line.
• CP6100 communicates with the Communications Management
Interface (CMI), which runs in one or more processors in the
NonStop System. System managers use CMI to establish and
change line configurations, start and stop lines, trace line
problems, monitor line quality and throughput, and balance the
communication workload among processors and controllers.
There is more information about CMI in Section 3.
File Management Interface
Applications use GUARDIAN file management procedures for access
to CP6100 lines. Application requests fall into two categories:
those that entail no interaction between the application and the
protocol task, and those that require such interaction.
Requests in the first category are really requests to the file
system, for example, to open a line and allow the application to
use it, to complete application requests in any order, or to find
out the last file system error related to the line. The specific
calls and their functions are as follows:
• AWAITIO waits for completion of an earlier request.
• DEVICEINFO reports the GUARDIAN device type and physical
record length of the line.
• FILEINFO reports the last file system error related to the
line, and tells how many processes are using the line.
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