Seems that launching AT+CSQF when not registered ends up timing out. AT+CSQF
is meant to be the fast version to get the signal quality, and is expected to
return instantly with the last cached signal quality value. But if we never
got registered, there is no such cached value, so it probably waits to get the
first one.
We must send ATZ alone and once reply received, wait some time before sending
the next initialization commands. Otherwise, the next commands will receive
garbage as reply. The only way to handle this is to override the whole generic
initialization phase.
We will also avoid sending any power-up command, as not needed.
Dan Williams
Aleksander Morgado