gps: improvements and corrections for config commands

This contains some improvements and corrections for the gps driver
It adds some additional functions for different modes (automobile, bike, etc)
and also ignores the return results from any config commands.

Basically due to the fact that there is a constant stream of updates
coming from NMEA messages, the results from sending any UBX commands
are getting lost. Better to just ignore them for now.

Signed-off-by: deadprogram <ron@hybridgroup.com>

gps/gpsparser.go

@@ -6,12 +6,28 @@ import (
 	"time"
 )
 
+type NMEASentenceType string
+
+const (
+	GSA NMEASentenceType = "GSA"
+	GGA NMEASentenceType = "GGA"
+	GLL NMEASentenceType = "GLL"
+	GSV NMEASentenceType = "GSV"
+	RMC NMEASentenceType = "RMC"
+	VTG NMEASentenceType = "VTG"
+	ZDA NMEASentenceType = "ZDA"
+	TXT NMEASentenceType = "TXT"
+)
+
 // Parser for GPS NMEA sentences.
 type Parser struct {
 }
 
 // Fix is a GPS location fix
 type Fix struct {
+	// Type is the NMEA sentence type that provided this fix.
+	Type NMEASentenceType
+
 	// Valid if the fix was valid.
 	Valid bool
 
@@ -53,6 +69,23 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 	}
 	typ := sentence[3:6]
 	switch typ {
+	case "GSV":
+		// https://docs.novatel.com/OEM7/Content/Logs/GPGSV.htm
+		fields := strings.Split(sentence, ",")
+		// GSV sentences have at least 4 fields, but typically 8, 12, 16, or 20 depending on satellites in view
+		if len(fields) < 4 {
+			return fix, errInvalidGSVSentence
+		}
+
+		fix.Type = GSV
+
+		// Number of satellites in view is always field 3
+		fix.Satellites = findSatellites(fields[3])
+
+		// GSV does not provide position, time, or fix validity
+		fix.Valid = false
+
+		return fix, nil
 	case "GGA":
 		// https://docs.novatel.com/OEM7/Content/Logs/GPGGA.htm
 		fields := strings.Split(sentence, ",")
@@ -60,6 +93,7 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 			return fix, errInvalidGGASentence
 		}
 
+		fix.Type = GGA
 		fix.Time = findTime(fields[1])
 		fix.Latitude = findLatitude(fields[2], fields[3])
 		fix.Longitude = findLongitude(fields[4], fields[5])
@@ -75,6 +109,7 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 			return fix, errInvalidGLLSentence
 		}
 
+		fix.Type = GLL
 		fix.Latitude = findLatitude(fields[1], fields[2])
 		fix.Longitude = findLongitude(fields[3], fields[4])
 		fix.Time = findTime(fields[5])
@@ -89,6 +124,7 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 			return fix, errInvalidRMCSentence
 		}
 
+		fix.Type = RMC
 		fix.Time = findTime(fields[1])
 		fix.Valid = (fields[2] == "A")
 		fix.Latitude = findLatitude(fields[3], fields[4])