Guru Meditation Error of type LoadProhibited occurred on core.

[tobz]

I'm running a basic all reading a distance from an HC-SR04 ultrasonic sensor, & after a shortish(irregular) amount of time the board crashes with the following message:

Guru Meditation Error of type Load Prohibited occurred on core  0. Exception was unhandled.                              
Register dump:                                                                                                          
PC      : 0x400869c6  PS      : 0x00060037  A0      : 0x80085b58  A1      : 0x3ff81c50                                  
A2      : 0x3ff81cac  A3      : 0x3ff81c70  A4      : 0x00000020  A5      : 0x3ffc397c                                  
A6      : 0x00000005  A7      : 0x3ffae010  A8      : 0xe67ec000  A9      : 0x3ffb6db8                                  
A10     : 0x3ff81cac  A11     : 0x3ffc3a88  A12     : 0x3ffb6db8  A13     : 0x3ffae020                                  
A14     : 0x3ffae040  A15     : 0x3ffae6c0  SAR     : 0x0000001f  EXCCAUSE: 0x0000001c                                  
EXCVADDR: 0xe67ec004  LBEG    : 0x4000c2e0  LEND    : 0x4000c2f6  LCOUNT  : 0x00000000                                  
                                                                                                                        
Backtrace: 0x400869c6:0x3ff81c50   

My code is based on this: https://github.com/mithru/MicroPython-Examples/blob/master/08.Sensors/HC-SR04/ultrasonic.py

Anyone have any idea what this means & what can be done about it?

[bucknall]

@tobz Can you please list where in your code that this error occurs?

[bucknall]

Please be aware that there are also a number of difference between the pyboard and the Pycom devices namely that Pycom doesn't use the pyb library and that a number of the standard classes/methods are different.

[tobz]

I think my issue might actaully be related to this post: https://forum.pycom.io/topic/1061/https-post-using-urequests-py-and-guru-mediation-error

the urequest class and nothing to do with the ultrasonic sensor.

[bucknall]

@tobz Ah ok, you are using the urequests library? We're looking into this.

Thanks!

[tobz]

@bucknall Cool. I'll follow along with that thread & hopefully that IS my issue and it gets resolved :)

[RobTuDelft]

@tobz Did you manage to get the HC-SR04 working after all?

[tobz]

@RobTuDelft yeah the sensor works fine (once I worked out you need a resistor in the circuit - derp). The crash appears to be caused by the urequest library (see https://forum.pycom.io/topic/1061/https-post-using-urequests-py-and-guru-mediation-error).

[RobTuDelft]

@tobz That's nice, could you share your code perhaps? Got one of these sensors coming in soon and would help to have a starting point.

[tobz]

@RobTuDelft sorry - I've been head down in work - will hopefully get some time later this week & post my code if you're still interested in it.

[tobz]

@RobTuDelft Here's the code I was using for the HC-SR04.
I hope it makes sense & works for you.

import machine
import time
import math
from machine import Timer

class Ultrasonic:
    def __init__(self, name, trigPin, echoPin, delay = 60):

        self.name = name
        self.triggerPin = trigPin
        self.echoPin = echoPin
        self.delay = delay

        self.last_distance = 0

        # Init trigger pin (out)
        self.trigger = machine.Pin(self.triggerPin)
        self.trigger.init(machine.Pin.OUT, None)
        self.trigger.value(False)

        # Init echo pin (in)
        self.echo = machine.Pin(self.echoPin)
        self.echo.init(machine.Pin.IN)

    def distance_in_inches(self):
        return (self.distance_in_cm() * 0.3937)

    def distance_in_cm(self):
        start = 0
        end = 0

        # Create a microseconds counter.
        micros = Timer.Chrono()
        micros.reset()
        micros.start()

        # Send a 10us pulse.
        self.trigger.value(True)
        Timer.sleep_us(10)
        self.trigger.value(False)

        # Wait 'till whe pulse starts.
        while self.echo.value() == 0:
            start = micros.read_us()

        # Wait 'till the pulse is gone.
        while self.echo.value() == 1:
            end = micros.read_us()

        # Deinit the microseconds counter
        micros.stop()

        # Calc the duration of the recieved pulse, divide the result by
        # 2 (round-trip) and divide it by 29 (the speed of sound is
        # 340 m/s and that is 29 us/cm).
        dist_in_cm = ((end - start) / 2) / 29

        return dist_in_cm

    def start(self, threshold, callback):
        print('Start reading Ultrasonic Sensor')
        while True:
            # get the current distance
            distance = self.distance_in_cm()

            # if the distance between this reading and the previous one
            # and the difference is greater than the threshold then
            # run the callback method
            if (math.fabs(self.last_distance - distance) > threshold):
                print("%s value: %s -> %s at %s" % (self.name, self.last_distance, distance, time.time()))

                if callback(self.name, distance) is True:
                    # set this readding as the previous reading for next run
                    self.last_distance = distance

            else:
                print("%s value: %s <-> %s at %s" % (self.name, self.last_distance, distance, time.time()))

            time.sleep(self.delay)

useage:

// init sensor, reading every 60 seconds
sensor = Ultrasonic('some-name', triggerPin, echoPin, 60)
sensor.start(changeThreshold, callbackMethod)

[tobru]

@tobz Thanks a lot for sharing the code. How did you connect the sensor to the board? You mentioned something about a resistor you had to use?

[tobz]

@tobru From memory I think it was a 10k resister - check the spec sheet for the HC-SR04. I probably just attached it straight onto the expansion board, maybe via a breadboard - I can't remember sorry.