core: gps: added field for HDOP to GPS data

HDOP is expressed in cm, meaning that an HDOP of 1.37m is stored as 137 in
the GPS data structure.

lib/minmea/include/minmea.h

@@ -271,6 +271,20 @@ static inline int minmea_toint(struct minmea_float *f)
     return f->value / f->scale;
 }
 
+/**
+ * Convert a fixed-point value to an integer value, applying an additional
+ * scaling factor.
+ * Returns zero for "unknown" values.
+ */
+static inline int minmea_toscaledint(struct minmea_float *f, const int scale)
+{
+    if(f->scale == 0)
+        return 0;
+
+    int_least32_t tmp = f->value * scale;
+    return tmp / f->scale;
+}
+
 #ifdef __cplusplus
 }
 #endif

openrtx/include/core/gps.h

@@ -54,6 +54,7 @@ typedef struct
     uint16_t   speed;                // Ground speed in km/h
     int16_t    tmg_mag;              // Course over ground, degrees, magnetic
     int16_t    tmg_true;             // Course over ground, degrees, true
+    uint16_t   hdop;                 // Horizontal dilution of precision, in cm
 }
 gps_t;
 

openrtx/src/core/gps.c

@@ -87,7 +87,6 @@ void gps_task(const struct gpsDevice *dev)
                 gps_data.timestamp.year = frame.date.year;
             }
 
-            gps_data.tmg_true = minmea_tofloat(&frame.course);
             gps_data.speed = KNOTS2KMH(minmea_toint(&frame.speed));
         }
         break;
@@ -110,6 +109,7 @@ void gps_task(const struct gpsDevice *dev)
             struct minmea_sentence_gsa frame;
             if (minmea_parse_gsa(&frame, sentence))
             {
+                gps_data.hdop = minmea_toscaledint(&frame.hdop, 100);
                 gps_data.fix_type = frame.fix_type;
                 for (int i = 0; i < 12; i++)
                 {