gps: export some errors for checking/supression from client

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

examples/gps/uart/main.go

@@ -8,7 +8,6 @@ import (
 )
 
 func main() {
-	println("GPS UART Example")
 	machine.UART1.Configure(machine.UARTConfig{BaudRate: 9600})
 	ublox := gps.NewUART(machine.UART1)
 	parser := gps.NewParser()
@@ -16,14 +15,24 @@ func main() {
 	for {
 		s, err := ublox.NextSentence()
 		if err != nil {
-			println(err)
-			continue
+			switch err {
+			case gps.ErrUnknownNMEASentence, gps.ErrInvalidNMEASentence, gps.ErrInvalidNMEASentenceLength:
+				continue
+			default:
+				println("sentence error:", err)
+				continue
+			}
 		}
 
 		fix, err = parser.Parse(s)
 		if err != nil {
-			println(err)
-			continue
+			switch err {
+			case gps.ErrUnknownNMEASentence, gps.ErrInvalidNMEASentence, gps.ErrInvalidNMEASentenceLength:
+				continue
+			default:
+				println("parse error:", err)
+				continue
+			}
 		}
 		if fix.Valid {
 			print(fix.Time.Format("15:04:05"))
@@ -43,7 +52,7 @@ func main() {
 			}
 			println()
 		} else {
-			println("No fix")
+			println("Waiting for fix...")
 		}
 		time.Sleep(200 * time.Millisecond)
 	}

gps/gps.go

@@ -11,16 +11,15 @@ import (
 )
 
 var (
-	errInvalidNMEASentenceLength = errors.New("invalid NMEA sentence length")
-	errInvalidNMEAChecksum       = errors.New("invalid NMEA sentence checksum")
-	errEmptyNMEASentence         = errors.New("cannot parse empty NMEA sentence")
-	errUnknownNMEASentence       = errors.New("unsupported NMEA sentence type")
+	ErrInvalidNMEASentenceLength = errors.New("invalid NMEA sentence length")
+	ErrInvalidNMEASentence       = errors.New("invalid NMEA sentence format")
+	ErrEmptyNMEASentence         = errors.New("cannot parse empty NMEA sentence")
+	ErrUnknownNMEASentence       = errors.New("unsupported NMEA sentence type")
 	errInvalidGGASentence        = errors.New("invalid GGA NMEA sentence")
 	errInvalidRMCSentence        = errors.New("invalid RMC NMEA sentence")
 	errInvalidGLLSentence        = errors.New("invalid GLL NMEA sentence")
 	errGPSCommandRejected        = errors.New("GPS command rejected (NAK)")
 	errNoACKToGPSCommand         = errors.New("no ACK to GPS command")
-	errInvalidNMEASentanceFormat = errors.New("invalid NMEA sentence format")
 )
 
 const (
@@ -151,15 +150,15 @@ func (gps *Device) WriteBytes(bytes []byte) {
 // It has to end with a '*' character following by a checksum.
 func validSentence(sentence string) error {
 	if len(sentence) < minimumNMEALength || sentence[0] != startingDelimiter || sentence[len(sentence)-3] != checksumDelimiter {
-		return errInvalidNMEASentenceLength
+		return ErrInvalidNMEASentenceLength
 	}
 	var cs byte = 0
 	for i := 1; i < len(sentence)-3; i++ {
 		cs ^= sentence[i]
 	}
 	checksum := strings.ToUpper(hex.EncodeToString([]byte{cs}))
-	if checksum != sentence[len(sentence)-2:len(sentence)] {
-		return errInvalidNMEASentanceFormat
+	if checksum != sentence[len(sentence)-2:] {
+		return ErrInvalidNMEASentence
 	}
 
 	return nil

gps/gpsparser.go

@@ -46,10 +46,10 @@ func NewParser() Parser {
 func (parser *Parser) Parse(sentence string) (Fix, error) {
 	var fix Fix
 	if sentence == "" {
-		return fix, errEmptyNMEASentence
+		return fix, ErrEmptyNMEASentence
 	}
 	if len(sentence) < 6 {
-		return fix, errInvalidNMEASentenceLength
+		return fix, ErrInvalidNMEASentenceLength
 	}
 	typ := sentence[3:6]
 	switch typ {
@@ -104,7 +104,7 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 		return fix, nil
 	}
 
-	return fix, errInvalidNMEASentanceFormat
+	return fix, ErrUnknownNMEASentence
 }
 
 // findTime returns the time from an NMEA sentence: