From cda2f3169e2974376b40ada5813324315c21e613 Mon Sep 17 00:00:00 2001
From: tracernz <michael.corcoran@outlook.com>
Date: Sat, 31 Jan 2015 18:08:36 +1300
Subject: [PATCH] Add NMEA $GPGSV Decoding for Sat Data

---
 src/main/io/gps.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/src/main/io/gps.c b/src/main/io/gps.c
index dfac15201..c2896d87d 100644
--- a/src/main/io/gps.c
+++ b/src/main/io/gps.c
@@ -452,6 +452,7 @@ bool gpsNewFrame(uint8_t c)
 #define NO_FRAME   0
 #define FRAME_GGA  1
 #define FRAME_RMC  2
+#define FRAME_GSV  3
 
 
 // This code is used for parsing NMEA data
@@ -533,6 +534,8 @@ static bool gpsNewFrameNMEA(char c)
     static uint8_t param = 0, offset = 0, parity = 0;
     static char string[15];
     static uint8_t checksum_param, gps_frame = NO_FRAME;
+    static uint8_t svMessageNum = 0;
+    uint8_t svSatNum = 0, svPacketIdx = 0, svSatParam = 0;
 
     switch (c) {
         case '$':
@@ -549,6 +552,8 @@ static bool gpsNewFrameNMEA(char c)
                     gps_frame = FRAME_GGA;
                 if (string[0] == 'G' && string[1] == 'P' && string[2] == 'R' && string[3] == 'M' && string[4] == 'C')
                     gps_frame = FRAME_RMC;
+                if (string[0] == 'G' && string[1] == 'P' && string[2] == 'G' && string[3] == 'S' && string[4] == 'V')
+                    gps_frame = FRAME_GSV;
             }
 
             switch (gps_frame) {
@@ -595,6 +600,49 @@ static bool gpsNewFrameNMEA(char c)
                             break;
                     }
                     break;
+                case FRAME_GSV:
+                    switch(param) {
+                      /*case 1:
+                            // Total number of messages of this type in this cycle
+                            break; */
+                        case 2:
+                            // Message number
+                            svMessageNum = grab_fields(string, 0);
+                            break;
+                        case 3:
+                            // Total number of SVs visible
+                            GPS_numCh = grab_fields(string, 0);
+                            break;
+                    }
+                    if(param < 4)
+                        break;
+
+                    svPacketIdx = (param - 4) / 4 + 1; // satellite number in packet, 1-4
+                    svSatNum    = svPacketIdx + (4 * (svMessageNum - 1)); // global satellite number
+                    svSatParam  = param - 3 - (4 * (svPacketIdx - 1)); // parameter number for satellite
+
+                    if(svSatNum > GPS_SV_MAXSATS)
+                        break;
+
+                    switch(svSatParam) {
+                        case 1:
+                            // SV PRN number
+                            GPS_svinfo_chn[svSatNum - 1]  = svSatNum;
+                            GPS_svinfo_svid[svSatNum - 1] = grab_fields(string, 0);
+                            break;
+                      /*case 2:
+                            // Elevation, in degrees, 90 maximum
+                            break;
+                        case 3:
+                            // Azimuth, degrees from True North, 000 through 359
+                            break; */
+                        case 4:
+                            // SNR, 00 through 99 dB (null when not tracking)
+                            GPS_svinfo_cno[svSatNum - 1] = grab_fields(string, 0);
+                            GPS_svinfo_quality[svSatNum - 1] = 0; // only used by ublox
+                            break;
+                    }
+                    break;
             }
 
             param++;