CP6100 I/O Process Programming Manual

Using CP6100: Programming
• Errors Unrelated to Specific Requests. You find out about
this kind of error when a READ call completes. The
application finds the error message in the READ buffer.
Errors reported in the READ buffer are normally line or
modem problems perceived by the protocol task: for example,
the number of line errors exceeds a threshold prescribed for
the line.
Some protocols, like BSC, do not support this feature. The
manual describing a protocol tells you the messages that
the protocol returns.
• Errors Related to Specific Requests. You find out about this
kind of error when a WRITEREAD call completes, and the buffer
contains an error message. The application finds the message
in the second byte of the buffer; a non-zero value identifies
the error that occurred.
An error in the WRITEREAD buffer signifies that the request
issued by your application was conveyed to the protocol task,
but for reasons indicated in the message, the request could
not be satisfied. The manual describing a protocol tells
you the messages that the protocol returns.
Notes on File System Errors. Figure 2-4 shows the file system
errors CP6100 can report. Appendix A describes them more fully,
giving for each the error number, a brief description of the
error and what caused it, and a corrective action you can take.
General Error Trapping and Recovery. The hierarchy among the
different kinds of errors and the ways they are reported makes
for an orderly error trapping and recovery procedure. A typical
way to complete a request and identify any errors is as follows:
1. The application calls AWAITIO to complete an earlier nowait
request.
2. If the READ or WRITEREAD completed with a condition code
other than zero, the application calls FILEINFO to discover
the error. Appendix A recommends means of recovery from file
system errors.
3. If a READ call completed with a condition code of zero, the
application examines the buffer, which contains an error or
other status message from the protocol task. If a WRITEREAD
call completed with a condition code of zero, the application
examines the buffer; it may or may not contain an error
message from the protocol task. Some protocols, for
October 1985
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