A Simple Example with pXRelay

A Simple Example with pXRelay

pXRelay is a simple MOOS app designed solely to illustrate basic functions of a MOOS app. It registers for a single variable, and upon receipt mail for that variable, it publishes another variable incremented by 1. It provides a framework for illustrating few other introductory topics.

Where to get more information:

• Type pXRelay—example on the command line.
• An Overview of MOOS-IvP and a Users Guide to the IvP Helm (Section 3.8) (PDF)

Basic pXRelay Usage

pXRelay is configured with its own block in the MOOS configuration file. It is configured with (a) an incoming variable, the variable it will register for incoming mail, and (b) an outgoing variable, a variable it will post an incremented integer each time it receives mail on the incoming variable. The basic form is:

 ProcessConfig = pXRelay
 {
   OUTGOING_VAR = 
   INCOMING_VAR = 
 } 

A Simple Example with pXRelay

The below mission file contains a configuration for two instances of the pXRelay application. All MOOS apps must have a unique name to connect to the MOOSDB, so we launch them with an alias with pAntler using the ~pXRelay_PEARS alias for example. The two apps each register for what the other produces, and each produces what the other registers for.

 // (wget http://oceanai.mit.edu/2.S998/examples/xrelay.moos)
 ServerHost = localhost
 ServerPort = 9000
 Community  = alpha

  ProcessConfig = ANTLER
  {
   MSBetweenLaunches = 200

   Run = MOOSDB       @ NewConsole = false
   Run = pXRelay      @ NewConsole = false ~pXRelay_PEARS
   Run = pXRelay      @ NewConsole = false ~pXRelay_APPLES
  }

  ProcessConfig = pXRelay_APPLES
  {
   AppTick       = 10
   CommsTick     = 10
   INCOMING_VAR  = APPLES
   OUTGOING_VAR  = PEARS
  }

  ProcessConfig = pXRelay_PEARS
  {
   AppTick       = 10
   CommsTick     = 10
   INCOMING_VAR  = PEARS
   OUTGOING_VAR  = APPLES
  } 

Upon launch, the two pXRelay apps are in a stalemate, each waiting for the other to make the first posting. We can break this stalemate with uPokeDB:

 $ uPokeDB xrelay.moos PEARS=1 

This should get things going. Now it would be good to see it all running by launching a scope:

 $ uXMS xrelay.moos --all --show=time