Random hard_fault on Boron

Hey everyone! I hope this is something stupid but I can’t for the life of me figure out what’s wrong. I have 2 Boron’s, one installed in a vehicle (functioning as a GPS tracker) and another one I’m using for development. Admittedly, though I’ve had the one Boron in service for about a year, I haven’t consistently checked the event logs. Since working on the new Boron I just got, I noticed them both hard_faulting at random times. The new Boron is just attached to my computer via USB and has a GPS sensor attached - that’s all.

I don’t know if this is an OS issue, library issue, or something with my code (though I’ve had someone with more experience than me say my code is ok). What should I try? What’s the best way to debug this?

Here’s my code:

// Getting the library
#include "AssetTracker.h"

// Timer variables: Used to keep track of the last time we published data
unsigned long lastPublish = 0;
unsigned long delayMinutes = 2; // Minuetes set to default on boot - adjust in code below for actual
unsigned long inactiveTime = 120; // Minutes inbetween notification when inactive

int turboSwitch = 0; //Function call changes - used to activate turbomode
int inactiveCount = 0; 

int acc_on_pin = D2;
//int disable_pin = D3; // Relay

// Creating an AssetTracker named 't' for us to reference
AssetTracker t = AssetTracker();

void setup() {
    pinMode(acc_on_pin, INPUT_PULLDOWN); // Pulldown resister included in Boron
    //digitalWrite(disable_pin, LOW);      // initialise the relay to off
    //pinMode(disable_pin, OUTPUT);
    // Sets up all the necessary AssetTracker bits

    // Enable the GPS module. Defaults to off to save power.
    // Takes 1.5s or so because of delays.
    //Particle.function("Disable", fuel_shutoff);
    Particle.function("turboMode", turboMode);

// Function turboMode - Record frequecy increase
int turboMode(String command) {
    if (command == "On") {
        turboSwitch = 1;
        return 1;
    else if (command == "Off") {
        turboSwitch = 0;
        return 0;
    else {return -1;}

void loop() {
    unsigned long now = millis();
    t.updateGPS();  // You'll need to run this every loop to capture the GPS output
    if (digitalRead(acc_on_pin) == HIGH) {
        delayMinutes = 2;
        inactiveCount = 0;
        if (turboSwitch == 1){
            delayMinutes = 1;
    } else {
        delayMinutes = inactiveTime;
     // if the current time - the last time we published is greater than your set delay...
    if ((now-lastPublish) >= delayMinutes*60*1000) {
        lastPublish = now; // Reset time
        if (t.gpsFix()) {
            //String pubAccel = String::format("%d,%d", coords, accStatus);
            //String datas = String::format("\"l\":%f", t.readLatLon());
            //Particle.publish("V1", datas, 60, PRIVATE);
            if (inactiveCount < 2){ // Don't report any new coordinates to reduce data after 2 
                  String::format("%.5f",t.readLatDeg()) +
                  "," + String::format("%.5f",t.readLonDeg()) +
                  "," + String::format("%.0f",t.getSpeed()),
                  60, PRIVATE);

I suggest you rather use AssetTrackerRK.
I’d also use snprintf() instead of String concatenations.

  char msg[32];
  snprintf(msg, sizeof(msg)
          , "%.5f,%.5f,%.0f"
          , t.readLatDeg()          
          , t.readLongDeg()          
          , t.getSpeed()
  Particle.publish("G", msg, PRIVATE);

Great! Thank you for the suggestions!. I’ll report back and see how that works.