Adding message observer can prevent arming and attribute listener updates

[hamishwillee]

@tcr3dr My initial test code for #445 is below. This adds a listener on_attribute for 'location' and a listener on_message for 'GLOBAL_POSITION_INT'.

The problem is that the on_message is not reporting any messages. Worse, if I enable it the vehicle will not arm (even though it reports is_armable) and only gives ONE update of the location information. Removing the offending code means that the example takes off and reports location as normal. You can verify this for yourself using the code below - simply (un)comment out the code marked up as #### DISABLE BELOW CODE TO ALLOW ARMING

The create_attribute.py still works, so probably I am doing something wrong here ... but even so, we need to know why because this is very odd.

from dronekit import connect
from dronekit.lib import VehicleMode, LocationGlobal
import time


#Set up option parsing to get connection string
import argparse  
parser = argparse.ArgumentParser(description='Print out vehicle state information. Connects to SITL on local PC by default.')
parser.add_argument('--connect', default='127.0.0.1:14550',
                   help="vehicle connection target. Default '127.0.0.1:14550'")
args = parser.parse_args()

# Connect to the Vehicle
print 'Connecting to vehicle on: %s' % args.connect
vehicle = connect(args.connect, wait_ready=True)
print "Got connected baby"

@vehicle.on_attribute('location')   
def listener(self, attr_name, value):
    # `attr_name` is the observed attribute (used if callback is used for multiple attributes)
    # `attr_name` - the observed attribute (used if callback is used for multiple attributes)
    # `value` is the updated attribute value.
    print "ATTR: %s changed to: %s" % (attr_name, value)
    print " GlobalF: %s" % self.location.global_frame
    print " LocalF: %s" % self.location.local_frame


#### DISABLE BELOW CODE TO ALLOW ARMING

# Create a message listener using the decorator.   
@vehicle.on_message('GLOBAL_POSITION_INT')
def listener(self, name, message):
    print "gpi alt: %s" % message.alt/1000
    print "gpi relative_alt: %s" % message.relative_alt/1000  

#### DISABLE ABOVE CODE TO ALLOW ARMING

# Create an attribute listener using the decorator.  
# If this changes but we don't get on_message notifications we know there is a problem
@vehicle.on_attribute('location')   
def listener(self, attr_name, value):
    # `attr_name` is the observed attribute (used if callback is used for multiple attributes)
    # `attr_name` - the observed attribute (used if callback is used for multiple attributes)
    # `value` is the updated attribute value.
    print " ATTR: %s changed to: %s" % (attr_name, value)




def arm_and_takeoff(aTargetAltitude):
    """
    Arms vehicle and fly to aTargetAltitude.
    """

    print "Basic pre-arm checks"
    # Don't let the user try to arm until autopilot is ready
    while not vehicle.is_armable:
        print " Waiting for vehicle to initialise..."
        print " GPS: %s" % vehicle.gps_0
        print " Is Armable?: %s" % vehicle.is_armable
        print " System status: %s" % vehicle.system_status.state
        print " Mode: %s" % vehicle.mode.name    # settable
        time.sleep(1)


    print "Arming motors"
    # Copter should arm in GUIDED mode
    vehicle.mode    = VehicleMode("GUIDED")
    vehicle.armed   = True    

    count_to_arm=0
    while not vehicle.armed:
        count_to_arm+=1    
        print " Waiting for arming...: %s" % count_to_arm
        print " GPS: %s" % vehicle.gps_0
        print " Is Armable?: %s" % vehicle.is_armable
        print " System status: %s" % vehicle.system_status.state
        print " Mode: %s" % vehicle.mode.name    # settable
        print " Armed: %s" % vehicle.armed
        vehicle.armed   = True   
        time.sleep(1)

    print "Taking off!"
    vehicle.commands.takeoff(aTargetAltitude) # Take off to target altitude

    # Wait until the vehicle reaches a safe height before processing the goto (otherwise the command 
    #  after Vehicle.commands.takeoff will execute immediately).
    while True:
        print " Altitude: ", vehicle.location.global_frame.alt      
        if vehicle.location.global_frame.alt>=aTargetAltitude*0.95: #Trigger just below target alt.
            print "Reached target altitude"
            break
        time.sleep(1)

arm_and_takeoff(20)


print "Going to first point..."
point1 = LocationGlobal(-35.361354, 149.165218, 20, is_relative=True)
vehicle.commands.goto(point1)

# sleep so we can see the change in map
time.sleep(30)

print "Going to second point..."
point2 = LocationGlobal(-35.363244, 149.168801, 20, is_relative=True)
vehicle.commands.goto(point2)

# sleep so we can see the change in map
time.sleep(30)

print "Returning to Launch"
vehicle.mode    = VehicleMode("RTL")

#Close vehicle object before exiting script
print "Close vehicle object"
vehicle.close()

[tcr3dr]

@hamishwillee Will you try this on the #445 branch? I added a try...except for the message listener case, which should give more insight into what is happening here. Perhaps it doesn't change anything though, in which case I'll investigate more deeply.

[hamishwillee]

Ah, problem is in the test code

@vehicle.on_message('GLOBAL_POSITION_INT')
def listener(self, name, message):
    print "gpi alt: %s" % message.alt/1000
    print "gpi relative_alt: %s" % message.relative_alt/1000  

So get

 ATTR: location changed to: <dronekit.lib.Locations object at 0x0000000007BC5F98>
>>> Exception in message handler for GLOBAL_POSITION_INT
>>> unsupported operand type(s) for /: 'str' and 'int'

All works if the value is changed to have

@vehicle.on_message('GLOBAL_POSITION_INT')
def listener(self, name, message):
    print "gpi alt: %s" % (message.alt/1000)
    print "gpi relative_alt: %s" % (message.relative_alt/1000)

My bad sorry. Closing.