In the normal functioning of ZCOM, transmission errors on
messages to terminal ZLUs are handled by the Mux interface card
firmware. The firmware always sends a status back to the driver
after it has processed a request - retries are handled internally.
The driver checks the mode of the send (i. e., send no wait, report
errors, etc.) to determine what to pass back to the requesting program.
If a power failure occurs or the Mux interface card crashes,
the driver receives an interrupt from the operating system. This
interrupt causes the driver to send a request to ZMON to download
the firmware to the particular interface card and to perform a full
restart sequence (which also involves re-sending any unacknowledged
messages). If the directory /var/opt/acc/dmp exists,
ZCOM will upload the contents of the Mux card memory and store it
in a file in this directory whenever a Mux card failure is detected.
This provides the ability to analyze firmware failures which can
be particularly valuable during the development of custom protocols.
For a detailed description of ZCOM C interface routine error
codes, please refer to the ACC Error Guide.
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