Remove the slave thread, set_callback already spawns a thread.
I2CSlave.callback() now puts the result (if valid) in a queue. This item
can be picked up by I2CMaster for further processing.
I2CMaster will wait 0.21s for a result in the queue. 0.21s, because I
always see a response in < 0.2s. If there is no result, it will send the
request again (max 20 retries). This is because I don't get reliable
responses (via pigpiod?). In an earlier commit I mentioned to configure
pigpiod with -s 2 (sample rate 2 microseconds). This doesn't seem to be
true. For example -s 10 gives the same reliability (and less CPU usage
by pigpiod).
--master-only allows to only run the I2C master functionality.
--slave-only allows to only run the I2C slave functionality.
The I2C slave functionality via the "set_callback" mechanism (--type
callback) just executes the pigpio "event_callback()" function and waits
for 2 seconds for a response. The amount of seconds can now be
configured via --slave-timeout.
Argument "--type [callback,wait]" is added to be able to switch between
"wait_for_event()" (previous functionality) and "event_callback()" in
the I2C slave functionality.
In a thread set_callback() executes event_callback() and just (very
dirty) sleeps 2 seconds to get a response or else cancels the event and
stops pigpio.
To get the most reliable output pigpiod is started with -s 2 (sample
rate 2 microseconds). Still most of the time too few bytes are received
on the "getdatalog" action (153 bytes expected).
