CP6100 I/O Process Programming Manual

Using CP6100: Programming
DATA COMMUNICATION ERRORS. A variety of communication problems
have the same symptom: a request from the Tandem system does not
bring an acknowledgment, or the reply received is unreasonable
given the communication protocol. The problems from which this
condition can result include failures of the communication line,
the modems, or the remote equipment, faulty configuration of
the line, the modems, or the remote equipment, traffic levels
sufficiently large to cause data overruns or synchronization
problems, and human oversights like forgetting to start a
terminal before you try to open it.
The most common strategy for dealing with the symptom is to try
the operation again, hoping the problem was a fluke and will not
recur. In describing a communication line to GUARDIAN (using the
SYSGEN program), you specify a reasonable timeout value for timed
requests, and a maximum number of retries the protocol task can
issue. Then if a line error occurs while your application is
running, the protocol task retries the request according to your
specifications. Only when the retry count is exhausted does the
protocol report an error.
APPLICATION ERROR HANDLING. There are three levels of errors
reported to an application: file system errors perceived by
CP6100; line or protocol errors related to specific application
requests; and line or protocol errors unrelated to specific
requests. These kinds of errors are reported in three different
ways:
• File System Errors. You find out about this kind of error
when a file system call completes with a non-zero condition
code. The application calls FILEINFO to discover the error.
A file system error usually means the call itself is invalid,
or that CP6100 cannot address the device you named. For
example, you issued a call (like CONTROL) not supported by
CP6100, the device you named does not exist, is down, or is
exclusive to another application, or a path switch occurred
during the request.
October 1985
2-12