65
Example #3: No response from the
old
board
n
#1
:2
A2
Board #2 becomes active
But the ‘^2’ response, telling that board #1 became inactive,
did not arrive! Where is the disorder? Maybe board #1
did
receive the
command and is indeed inactive, just the ‘^2’ response was lost, and
everything is OK (case #1); but maybe board #1 did
not receive the
command and
both boards are active (case #2). This is a dangerous
situation and definitely should be avoided. This problem is more
complicated than the previous one (in example #2) – sometimes re-sending
the ‘:2’ command won’t help: In case #2 re-sending the ‘:2’ command
should be responded by ‘^2’ which indicates that everything is OK. (‘!2’
will be responded as well, but this does not add us any new information.)
However, if the ‘^2’ response does not arrive, we have to use the ‘n’
command in order to make sure that we are not in the situation of two
boards active at the same time, which should be avoided. Therefore, we
should send the ‘n’ command and expect to get
only ‘*2’ (and not ‘*1’).
Although it’s time consuming, we have to repeat the ‘n’ command at least
once in order to have no doubt that board #1 is really inactive.
