Guardian Programmer's Guide

Communicating With Terminals
Guardian Programmer’s Guide — 421922-014
10 - 36
Recovering From Errors
! Do some computation -- this code could be any non-
! interactive task:
J := 0;
WHILE J < 2000 DO
BEGIN
I := 0;
WHILE I < 2000 DO
I := I + 1;
J := J + 1;
END;
END;
END;
END;
Recovering From Errors
For terminals, error recovery depends on the specific error. Possible errors can be
categorized as follows
• Errors that can be retried indefinitely
• Errors that should be retried but only a limited number of times
• Errors that need special attention
• Errors for which retrying the operation makes no sense
The following errors can be retried indefinitely. This can be important because in some
situations a read operation, for example, might not complete for several days:
Errors 201 through 229 should be retried a limited number of times. These errors
indicate an error in the path to the terminal. Typically, you should retry these errors
between 3 and 10 times.
The following errors often need special attention:
112 Operation preempted by operator message
230 CPU power failed, then restored
231 Controller power failed then restored
246-
24
9
Expand errors
30-39 Temporary lack of resources
40 Operation timed out
110 and
111
BREAK errors
112 Preempted by operator message
140 Modem error