Energy to join a network when it is present is roughly constant - joining is either faster but at higher current, or slower but at lower current.  In some cases however, e.g. when there is the possibility that the network may not be present for long periods of time, it may be desirable to listen for a short period of time, then return to a low power mode for a longer period, waking periodically to listen for the network.  Normally, the mote uses the joinDutyCycle parameter stored in its persistent parameter settings (default = 64 or 25%), and will listen continuously at this duty cycle until it joins a network.  The 01-join_control sample application relies on the local module to handle joining, but modifies the joinDutyCycle while the mote remains searching for the network. 

The 01-join_control Sample Application

The application is best used with the manager initially turned off. The application cycles through listening at 100%, 5%, and sitting in idle (burning a few µA).  

Join app, ver 1.2.0.1
SmartMeshIP stack, ver 1.4.1.6
Setting Join duty cycle to 100%
Setting Join Duty Cycle to 5%
Stop listening and return to idle state
Starting to try joining again...
Setting Join duty cycle to 100%
...

You can also turn on the mac trace to see the radio listening (and at what duty cycle) during active periods.

> mtrace mac on
listen chan = 0, dc=100
listen chan = 6, dc=100
listen chan = 4, dc=100
Setting Join Duty Cycle to 5%
listen chan = 5, dc=5
listen chan = 2, dc=5
listen chan = 9, dc=5
...

After a few cycles, turn on the manager and the mote will join. It will print the following once joined:

I finally joined!

Implementation Details

The 01-join_control sample application uses the Helper Modules to initialize the CLI Module and interact with the local interface. In particular, it configures the loc_task helper module to join the network  - it stops the local module from opening a socket by passing NULL in the port field. 

It uses a single task (joinTask) which, in a while(1) loop:

• Sets the joinDutyCycle to 100% and pends on the joinedSem semaphore with a timeout HI_TIMEOUT
• If the timeout is reached, it sets the joinDutyCycle to 5% and pends on the joinedSem semaphore with a timeout LOW_TIMEOUT
• If the timeout is reached, it issues the dn_loc_stopSearchCmd() and waits for IDLE_TIMEOUT
• It then issues dnm_loc_joinCmd() to start the mote listening for a network and repeats the loop
• If the mote successfully joins, it prints a success message (repeatedly) and doesn't modify the join duty cycle further