Application Programming Interface Module

The ait.core.api module provides an Application Programming Interface (API) to your instrument by bringing together the core.cmd and core.tlm modules in a complementary whole, allowing you to script instrument interactions. The two primary tools in the api module that you’ll use for scripting instrument interactions are the ait.core.api.Instrument class and the ait.core.api.wait() function.


The ait.core.api.Instrument class brings together AIT’s commanding and telemetry tools into a single interface. With this you can monitor multiple telemetry packet streams and send commands to your instrument. Let’s look at a few examples.

First we’ll instantiate an instance of our Instrument with the default commanding and telemetry connections:

my_instrument = ait.core.api.Instrument()

We can access telemetry via the tlm attribute. We’ll assume that we have a packet called AIT_EHS defined in our tlm.yaml file:

telem = my_instrument.tlm.AIT_EHS

# print the number of AIT_EHS packets we've received

Let’s suppose we have a telemetry field defined in AIT_EHS called CmdsRcvd which keeps track of how many commands the instrument has received. We could pull that out of the most recently received telemetry packet with:


Let’s send a command to our instrument. We’ll assume we have a “no op” command defined as AIT_NO_OP in our cmd.yaml file. You can access the commanding functionality via the cmd attribute:


If our command required arguments we could specify them a number of ways:

my_instrument.cmd.send('AIT_SET_OP_MODE PAYLOAD_SAFE')
my_instrument.cmd.send('AIT_SET_OP_MODE', 'PAYLOAD_SAFE')
my_instrument.cmd.send('AIT_SET_OP_MODE', mode='PAYLOAD_SAFE')


The blis.core.api.wait() function allows us to halt execution in a script until a specified number of seconds have passed or until a supplied condition evaluates to True.

Wait until 2 seconds have passed:


Wait until telemetry tells us that two commands have been received:

wait('my_instrument.tlm.AIT_EHS.CmdsRcvd == 2')

Expressions can be specified as a string (as above), a lambda, or as a function. All 3 of the following are equivalent:

# Using a string
wait('my_instrument.tlm.AIT_EHS.CmdsRcvd == 2')

# Using a lambda expression
wait(lambda: my_instrument.tlm.AIT_EHS.CmdsRcvd == 2)

# Using a function
def twoCmdsRcvd(): return my_instrument.tlm.AIT_EHS.CmdsRcvd == 2

Putting it all Together

Below we’ll create an example script to do a simple test of the API to ensure that we can read telemetry from our instrument, send it a command, and react to changes in the telemetry.

#!/usr/bin/env python

from ait.core import log
from ait.core.api import Instrument, wait

inst = Instrument()

# Wait (forever) until we have have at least two EHS packets.
wait(lambda: len(inst.tlm.AIT_EHS) > 2)

# Send a command

# The packet buffer may be accessed directly for the current
# packet.  The current packet may also be accessed via subscript
# zero.  For example, the following are equivalent:
#   inst.tlm.AIT_EHS.CmdCmdsRcvd == inst.tlm.AIT_EHS[0].CmdCmdsRcvd
# Older packets are accessed using increasing subscripts, e.g.
# the penultimate received packet is accessed via:
#   inst.tlm.AIT_EHS[1].CmdCmdsRcvd
# Here we'll wait until telemetry tells us that it received our
# command or we'll timeout (and raise an Exception) if we wait
# 5 seconds and nothing happens.
if wait('inst.tlm.AIT_EHS.CmdCmdsRcvd == inst.tlm.AIT_EHS[1].CmdCmdsRcvd + 1', timeout=5):'Command received')