•
Forgetting to program for these error conditions is a common mistake. Even though you think your code
will never make a mistake, take advantage of the feedback that the Base Station provides.
•
Parse the Returned Strings thoroughly
. Don't assume anything about the next response from the Base
to your program and look only for the partial string such as the ID only; parse the returned string
completely and be sure you are examining every possibility. Failure to do so is a common mistake.
•
Plan for expansion
. You may start small (1 Base/1 Terminal) but try to create an application that will
allow for easy expansion and addition - especially of Terminals.
•
Site Evaluation
. Site Testing does not require that you have an application up and running and can save
you time when you do sit down to create your program if you already know what you will be dealing
with in terms of Base Stations and Relays.
•
Use the Demo Programs
. The demo programs can at least allow you to see how the system functions
and whether you can anticipate any system-wide problems. The demo programs should also be used as a
response-time benchmark.
Planning For Failures
Hardware Failures
Let's assume that each part of the system has failed. How are you going to know what has happened and how are
you going to recover?
•
The most frequent failures are at the Terminal level. If a Terminal has a hardware failure, it will not be
able to
SIGN OUT
. It is possible for the Terminal operator to press the ON/OFF key or the F1 key by
accident, forcing the Terminal to
SIGN OUT
- sometimes in the middle of a transaction. This happens at
battery-changing time also. You need to plan for partial transactions – do you trash the data you do have
and start over, or pick up where you left off?
•
Keep in mind that if a Terminal has
SIGN
ed
OUT
in mid-transaction, the Base Station clears any pending
message for that Terminal before it will allow it to
SIGN ON
again. Make allowances to re-send
messages or prompts that were cleared upon
SIGN ON
if necessary.
•
Relay Station failures are often cable-related. If a Terminal puts out a "Who Can Hear Me?" message
and a Relay that is for some reason not connected to the Base Station (bad cable, cut cable, broken
connectors) hears it, it answers with the message:
Relay n Cannot Be
Heard by the Base
Notify Supervisor
Press Any Key
At this point, it is up to the operator to notify someone that the Relay is not communicating with the Base and to
check the cabling first. There is no message sent to the host, so it is very important that the operator that receives
this message notify someone immediately.
Operator Errors
•
Plan on your operator walking out of range and going to lunch in the middle of a transaction. What do
you do with the data you do have, and where are you going to start up again?
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