Unable to get past an `App fault!` when running trig calculations in the cloudpebble emulator

Watchapp/Face Developers Corner
1

I’m trying to design a watchface using cloudpebble, and I’m struggling to get going.
My idea requires doing some calculations for finding the current sun position in the sky, but I can’t seem to use trigonometry functions consistently without crashing with an App fault! message, like this one:
[ERROR] ault_handling.c:99: App fault! {8a392ece-5518-4876-9eb6-c5d2e01f3c79} PC: 0x30f2 LR: 0x1

I also haven’t been able to isolate the problem to a specific trig function, or a specific input value that causes issues, as it seems very sensitive to contextual changes (as in, just calling the exact same function from a different place, or a different number of times, can cause the issue to appear or disappear).

My main.hfile consists of the first beginner demo, with my suncalc.h included, and with a call to my problemsolar_lunar_data function inside the update_time function.

This is a subsection of the problem code:

#include <math.h>
#include <pebble.h>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif


typedef struct
{
    double solar_midnight;
    double sunrise;
    double solar_noon;
    double sunset;
    double lunar_max_height;
    double lunar_min_height;
    int moon_phase;
} SolarLunarData;


SolarLunarData compute_solar_lunar_data(double latitude_degrees,
                                        double longitude_degrees,
                                        unsigned int current_unix_timestamp)
{
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 1");
    // ============================================================
    // SECTION 1 — CONSTANTS AND TIME CONVERSION
    // ============================================================
    const double seconds_per_day = 86400.0;
    const double unix_to_julian_offset = 2440587.5;

    double julian_date = ((double)current_unix_timestamp / seconds_per_day) + unix_to_julian_offset;
    double days_since_j2000 = julian_date - 2451545.0;

    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2");
    // ============================================================
    // SECTION 2 — SOLAR POSITION CALCULATIONS
    // ============================================================
    double mean_solar_longitude = fmod(280.460 + 0.9856474 * days_since_j2000, 360.0);
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.1");

    double mean_anomaly_sun = fmod(357.528 + 0.9856003 * days_since_j2000, 360.0);
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.2");

    double mean_anomaly_radians = mean_anomaly_sun * M_PI / 180.0;
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.3");

    double ecliptic_longitude = mean_solar_longitude
        + 1.915 * sin(mean_anomaly_radians)
        + 0.020 * sin(2.0 * mean_anomaly_radians);
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.4");
  
    double ecliptic_longitude_radians = ecliptic_longitude * M_PI / 180.0;
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.5");
  
    double obliquity_radians = (23.439 - 0.0000004 * days_since_j2000) * M_PI / 180.0;
    APP_LOG(APP_LOG_LEVEL_DEBUG, "section 2.6");

(If you’re curious, this was originally a much more tidy and complete suncalc implementation, but I shoved all the stuff I needed into a single function to try pinpointing the issue I’m having).

As you can see, I stuck a bunch of APP_LOGs in there to try and identify the point where the function stops running. This is what gets printed to the log:

[DEBUG] suncalc.h:32: section 1
[DEBUG] suncalc.h:42: section 2
[DEBUG] suncalc.h:47: section 2.1
[DEBUG] suncalc.h:50: section 2.2
[DEBUG] suncalc.h:53: section 2.3
[ERROR] ault_handling.c:99: App fault! {8a392ece-5518-4876-9eb6-c5d2e01f3c79} PC: 0x30f2 LR: 0x1

During a previous run of the same code, it only got to section 2.2 before crashing, but it seems like it usually gets to section 2.3 now…

Anyways, I haven’t tried setting up a (non-cloudpebble) development environment for Pebble on my PC yet, but that’s probably going to be my next step. I have to stop debugging for now, just to preserve my sanity, but I wanted to post this first, in case anyone here happens to have any insight they can offer :sweat_smile:

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2

The Pebble C API doesn’t support the usual trigonometry functions sin(), cos() etc. but instead has sin_lookup(), cos_lookup() and atan2_lookup() functions with pre-computed tables:

And a question: do you intend to publish your suncalc implementation as open source? I would be very interested in this :slight_smile:

2 Likes
3

Oh my god, thank you! I was able to get the function to return by substituting some approximation functions in place of the real trig functions.

I might open source it. The logic in my current code is based on my MicroPython suncalc port suncalc.mpy, which itself is based on a Python/numpy port of suncalc.js. I was planning on converting it into a suncalc.h, which I would then publish separately from my Pebble app, for anyone who wanted something like that… But right now, my fixed code completely sucks and doesn’t have most of the features of the source suncalc modules :sweat_smile:
I might still open-source my junky code anyways. Or, maybe I’ll make a nice Pebble-specific suncalc.h module I can share; I’ll have to think about it! (and see how much time/energy I’ve got!)

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