GPS NMEA: generate empty GSA sentence for dead reckoning fixes

For dead reckoning fixes when number of SV used in fix is 0,
we need to generate an empty GSA sentence

CRs-fixed: 2542163

Change-Id: Icb89981d04ecdfeb81fbdc16b2a8d3676319b18d

1 files changed, 8 insertions, 0 deletions

diff --git a/utils/loc_nmea.cpp b/utils/loc_nmea.cpp
index 24197ff..64a3525 100644
--- a/utils/loc_nmea.cpp
+++ b/utils/loc_nmea.cpp
@@ -1327,6 +1327,14 @@ void loc_nmea_generate_pos(const UlpLocation &location,
             talker[1] = sv_meta.talker[1];
         }
 
+        // if svUsedCount is 0, it means we do not generate any GSA sentence yet.
+        // in this case, generate an empty GSA sentence
+        if (svUsedCount == 0) {
+            strlcpy(sentence, "$GPGSA,A,1,,,,,,,,,,,,,,,,", sizeof(sentence));
+            length = loc_nmea_put_checksum(sentence, sizeof(sentence));
+            nmeaArraystr.push_back(sentence);
+        }
+
         char ggaGpsQuality[3] = {'0', '\0', '\0'};
         char rmcModeIndicator = 'N';
         char vtgModeIndicator = 'N';