gps.cpp

#include "gps.h"
#include <TinyGPSPlus.h>
#include <Arduino.h>

// A TinyGPSPlus field stays "valid" forever once it has been set, so age is the
// thing that actually says the fix is live. The module reports at 1 Hz, so two
// missed updates and we stop trusting it.
static const uint32_t FIX_MAX_AGE_MS = 2000;

// Deliberately not static: the host stub's encode() parses no NMEA, so
// test/test_drivers.cpp declares this extern and sets the fix fields directly.
TinyGPSPlus gps;

void initGPS() {
    Serial1.begin(9600);
}

void updateGPS() {
    while (Serial1.available() > 0) {
        gps.encode((char)Serial1.read());   // available() rules out the -1
    }
}

bool gpsHasFix() {
    return gps.location.isValid() && gps.location.age() < FIX_MAX_AGE_MS;
}

// TinyGPSPlus works in double throughout. The narrowing to float is deliberate
// - it matches the rest of the flight code and costs about a metre of position
// resolution - so it is spelled out rather than left to the compiler.
float gpsLatitude() {
    return gpsHasFix() ? (float)gps.location.lat() : 0.0f;
}

float gpsLongitude() {
    return gpsHasFix() ? (float)gps.location.lng() : 0.0f;
}

// NMEA carries speed over ground in knots; mps() is TinyGPSPlus's conversion.
float gpsGroundSpeed() {
    if (!gps.speed.isValid() || gps.speed.age() >= FIX_MAX_AGE_MS) {
        return 0.0f;
    }
    return (float)gps.speed.mps();
}

float gpsCourse() {
    if (!gps.course.isValid() || gps.course.age() >= FIX_MAX_AGE_MS) {
        return 0.0f;
    }
    return (float)gps.course.deg();
}