THC Basics

THC - Basics

Main control loop

Once THC completed the setup phase it enters forever into the main control loop. In an interval defined by thc::HeartBeatMS the following sequence is executed:

• The device states and device events are updated
• The jobs scheduled for the current time are executed

Device states and events

Each heartbeat interval the device states and device events are updated. The device state is available for custom scripts and tasks via the thc::State array variable:

 thc::State(<DeviceName>)

Example:

 puts $thc::State(Siren,state)
 -> 0
 puts $thc::State(MotionLiving,battery)
 -> 80

The thc::Event array variable that is also updated every heartbeat will contain during a single heartbeat interval the state value of a device if the state is switched to a new valid value (non ""). Transitions from and to non valid values ("") are filtered: A transition from an initial state value to an invalid value ("") and back to the initial value will not generate an event. However a transition from a first value to an invalid value, and then to a last value that is different from the first value, will generate an event.

 _____???_____???-------???----???_________---------________
                 ^                ^        ^        ^
                 |Event=1         |Event=0 |Event=1 |Event=0

Example:

 thc::DefineJob -tag Surv -description "Surveillance" {
    if {$thc::Event(MySensor)==1} {
       thc::Set {Sirene,state LightLiving,state} 1 }
 }

Finally, for devices that have been declared with the -sticky option (see thc::DefineDevice) the first occurring device state that is valid and non-zero is also stored in the array variable thc::StickyState. The sticky state variable can be cleared with the command thc::ResetStickyStates, which needs to be called by a custom job.

The sticky state variable allows capturing over a certain period the occurrence of an event, to log the event then by a longer interval job. Logging functions like thc::Rrd::Log log typically the sticky state values instead of the instantaneous state, for devices that have a sticky state. Example:

 thc::DefineJob -tag RrdLog -time +1m -repeat 1m -description "RRD log" {
    thc::Rrd::Log
    thc::ResetStickyStates }