GPS: using 16-bit integers for altitude and speed

lib/minmea/include/minmea.h

@@ -258,6 +258,19 @@ static inline float minmea_tocoord(struct minmea_float *f)
  */
 int minmea_tofixedpoint(struct minmea_float *f);
 
+
+/**
+ * Convert a fixed-point value to an integer value.
+ * Returns zero for "unknown" values.
+ */
+static inline int minmea_toint(struct minmea_float *f)
+{
+    if(f->scale == 0)
+    return 0;
+
+    return f->value / f->scale;
+}
+
 #ifdef __cplusplus
 }
 #endif

openrtx/include/core/gps.h

@@ -50,8 +50,8 @@ typedef struct
     uint32_t   active_sats;          // Bitmap representing which sats are part of the fix
     int32_t    latitude;             // Latitude coordinates
     int32_t    longitude;            // Longitude coordinates
-    float      altitude;             // Antenna altitude above mean sea level (geoid) in m
+    int16_t    altitude;             // Antenna altitude above mean sea level (geoid) in m
-    float      speed;                // Ground speed in km/h
+    uint16_t   speed;                // Ground speed in km/h
     float      tmg_mag;              // Course over ground, degrees, magnetic
     float      tmg_true;             // Course over ground, degrees, true
 }

openrtx/src/core/gps.c

@@ -26,7 +26,7 @@
 #include <string.h>
 #include <stdbool.h>
 
-#define KNOTS2KMH 1.852f
+#define KNOTS2KMH(x) ((((int) x) * 1852) / 1000)
 
 static char sentence[2*MINMEA_MAX_LENGTH];
 static bool gpsEnabled        = false;
@@ -102,7 +102,7 @@ void gps_task()
             }
 
             gps_data.tmg_true = minmea_tofloat(&frame.course);
-            gps_data.speed = minmea_tofloat(&frame.speed) * KNOTS2KMH;
+            gps_data.speed = KNOTS2KMH(minmea_toint(&frame.speed));
         }
         break;
 
@@ -113,7 +113,7 @@ void gps_task()
             {
                 gps_data.fix_quality = frame.fix_quality;
                 gps_data.satellites_tracked = frame.satellites_tracked;
-                gps_data.altitude = minmea_tofloat(&frame.altitude);
+                gps_data.altitude = minmea_toint(&frame.altitude);
             }
         }
         break;
@@ -166,7 +166,7 @@ void gps_task()
             struct minmea_sentence_vtg frame;
             if (minmea_parse_vtg(&frame, sentence))
             {
-                gps_data.speed = minmea_tofloat(&frame.speed_kph);
+                gps_data.speed = minmea_toint(&frame.speed_kph);
                 gps_data.tmg_mag = minmea_tofloat(&frame.magnetic_track_degrees);
                 gps_data.tmg_true = minmea_tofloat(&frame.true_track_degrees);
             }

openrtx/src/core/voicePromptUtils.c

@@ -673,7 +673,7 @@ void vp_announceGPSInfo(vpGPSInfoFlags_t gpsInfoFlags)
     if ((gpsInfoFlags & vpGPSSpeed) != 0)
     {
         // speed/altitude:
-        sniprintf(buffer, 16, "%4.1fkm/h", state.gps_data.speed);
+        sniprintf(buffer, 16, "%dkm/h", state.gps_data.speed);
         vp_queuePrompt(PROMPT_SPEED);
         vp_queueString(buffer, vpAnnounceCommonSymbols |
                                vpAnnounceLessCommonSymbols);
@@ -683,7 +683,7 @@ void vp_announceGPSInfo(vpGPSInfoFlags_t gpsInfoFlags)
     {
         vp_queuePrompt(PROMPT_ALTITUDE);
 
-        sniprintf(buffer, 16, "%4.1fm", state.gps_data.altitude);
+        sniprintf(buffer, 16, "%dm", state.gps_data.altitude);
         vp_queueString(buffer, vpAnnounceCommonSymbols);
         addSilenceIfNeeded(flags);
     }

openrtx/src/ui/default/ui.c

@@ -63,6 +63,7 @@
 
 #include <stdio.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <math.h>
 #include <ui/ui_default.h>
 #include <rtx.h>
@@ -1269,8 +1270,8 @@ void ui_saveState()
 }
 
 #ifdef CONFIG_GPS
-static float priorGPSSpeed = 0;
+static uint16_t priorGPSSpeed = 0;
-static float priorGPSAltitude = 0;
+static int16_t  priorGPSAltitude = 0;
 static float  priorGPSDirection = 500; // impossible value init.
 static uint8_t priorGPSFixQuality= 0;
 static uint8_t priorGPSFixType = 0;
@@ -1300,15 +1301,13 @@ static vpGPSInfoFlags_t GetGPSDirectionOrSpeedChanged()
         priorGPSFixType = state.gps_data.fix_type;
     }
 
-    float speedDiff=fabs(state.gps_data.speed - priorGPSSpeed);
+    if (state.gps_data.speed != priorGPSSpeed)
-    if (speedDiff >= 1)
     {
         whatChanged |= vpGPSSpeed;
         priorGPSSpeed = state.gps_data.speed;
     }
 
-    float altitudeDiff = fabs(state.gps_data.altitude - priorGPSAltitude);
+    if (state.gps_data.altitude != priorGPSAltitude)
-    if (altitudeDiff >= 5)
     {
         whatChanged |= vpGPSAltitude;
         priorGPSAltitude = state.gps_data.altitude;

openrtx/src/ui/default/ui_menu.c

@@ -707,7 +707,7 @@ void _ui_drawMenuGPS()
         gfx_print(layout.line2_pos, layout.top_font, TEXT_ALIGN_RIGHT,
                   color_white, "%d.%.6d", longitude_int, longitude_dec);
         gfx_print(layout.bottom_pos, layout.bottom_font, TEXT_ALIGN_CENTER,
-                  color_white, "S %4.1fkm/h  A %4.1fm",
+                  color_white, "S %dkm/h  A %dm",
                   last_state.gps_data.speed,
                   last_state.gps_data.altitude);
     }