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simplified NMEA checksum handling, also append checksum to POGNS mess…
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@b3nn0
b3nn0 committed Jan 15, 2021
1 parent 0d09823 commit 2c1a002
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Showing 3 changed files with 48 additions and 49 deletions.
76 changes: 33 additions & 43 deletions main/flarm-nmea.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,19 @@ func sendNetFLARM(msg string) {

}

// Append checksum and to nmea string
func appendNmeaChecksum(nmea string) string {
start := 0
if nmea[0] == '$' {
start = 1
}
checksum := byte(0x00)
for i := start; i < len(nmea); i++ {
checksum = checksum ^ byte(nmea[i])
}
return fmt.Sprintf("%s*%02X", nmea, checksum)
}

func makeFlarmPFLAUString(ti TrafficInfo) (msg string) {
// syntax: PFLAU,<RX>,<TX>,<GPS>,<Power>,<AlarmLevel>,<RelativeBearing>,<AlarmType>,<RelativeVertical>,<RelativeDistance>,<ID>
gpsStatus := 0
Expand Down Expand Up @@ -70,16 +83,12 @@ func makeFlarmPFLAUString(ti TrafficInfo) (msg string) {
}
// TODO: we are always airbourne for now
if alarmLevel > 0 {
msg = fmt.Sprintf("PFLAU,%d,1,%d,1,%d,%d,%d,%d,%d,%s", len(traffic), gpsStatus, alarmLevel, int32(bearing), alarmType, relativeVertical, int32(math.Abs(dist)), idstr)
msg = fmt.Sprintf("$PFLAU,%d,1,%d,1,%d,%d,%d,%d,%d,%s", len(traffic), gpsStatus, alarmLevel, int32(bearing), alarmType, relativeVertical, int32(math.Abs(dist)), idstr)
} else {
msg = fmt.Sprintf("PFLAU,%d,1,%d,1,0,,0,,,", len(traffic), gpsStatus)
msg = fmt.Sprintf("$PFLAU,%d,1,%d,1,0,,0,,,", len(traffic), gpsStatus)
}

checksumPFLAU := byte(0x00)
for i := range msg {
checksumPFLAU = checksumPFLAU ^ byte(msg[i])
}
msg = (fmt.Sprintf("$%s*%02X\r\n", msg, checksumPFLAU))
msg = appendNmeaChecksum(msg)
msg += "\r\n"
return
}

Expand Down Expand Up @@ -154,9 +163,8 @@ func makeFlarmPFLAAString(ti TrafficInfo) (msg string, valid bool, alarmLevel ui
F = static object
*/

var idType, checksum uint8
var idType uint8
var relativeNorth, relativeEast, relativeVertical, groundSpeed int32
var msg2 string

// Addr type "NON-ICAO" mapped to Flarm ID, rest mapped to ICAO.
// Especially SkyDemon is picky and only accepts NMEA messages with 0-2, but nothing else.
Expand Down Expand Up @@ -213,22 +221,14 @@ func makeFlarmPFLAAString(ti TrafficInfo) (msg string, valid bool, alarmLevel ui
}

if ti.Position_valid {
msg = fmt.Sprintf("PFLAA,%d,%d,%d,%d,%d,%s,%d,%d,%d,%0.1f,%s", alarmLevel, relativeNorth, relativeEast, relativeVertical, idType, idstr, uint16(ti.Track), uint16(ti.TurnRate), groundSpeed, climbRate, acType)
msg = fmt.Sprintf("$PFLAA,%d,%d,%d,%d,%d,%s,%d,%d,%d,%0.1f,%s", alarmLevel, relativeNorth, relativeEast, relativeVertical, idType, idstr, uint16(ti.Track), uint16(ti.TurnRate), groundSpeed, climbRate, acType)
} else {
msg = fmt.Sprintf("PFLAA,%d,%d,,%d,%d,%s,,,,%0.1f,%s", alarmLevel, int32(math.Abs(dist)), relativeVertical, idType, idstr, climbRate, acType) // prototype for bearingless traffic
msg = fmt.Sprintf("$PFLAA,%d,%d,,%d,%d,%s,,,,%0.1f,%s", alarmLevel, int32(math.Abs(dist)), relativeVertical, idType, idstr, climbRate, acType) // prototype for bearingless traffic
}
//msg = fmt.Sprintf("PFLAA,%d,%d,%d,%d,%d,%X!%s,%d,,%d,%0.1f,%d", alarmLevel, relativeNorth, relativeEast, relativeVertical, idType, ti.Icao_addr, ti.Tail, ti.Track, groundSpeed, climbRate, acType)

for i := range msg {
checksum = checksum ^ byte(msg[i])
}
msg = (fmt.Sprintf("$%s*%02X\r\n", msg, checksum))
msg = appendNmeaChecksum(msg)
msg += "\r\n"

checksum = 0 // reset for next message
for i := range msg2 {
checksum = checksum ^ byte(msg2[i])
}
msg = msg
valid = true
return
}
Expand Down Expand Up @@ -318,16 +318,12 @@ func makeGPRMCString() string {
var msg string

if isGPSValid() {
msg = fmt.Sprintf("GPRMC,%02.f%02.f%05.2f,%s,%010.5f,%s,%011.5f,%s,%.1f,%.1f,%02d%02d%02d,%s,%s,%s", hr, mins, sec, status, lat, ns, lng, ew, gs, trueCourse, dd, mm, yy, magVar, mvEW, mode)
msg = fmt.Sprintf("$GPRMC,%02.f%02.f%05.2f,%s,%010.5f,%s,%011.5f,%s,%.1f,%.1f,%02d%02d%02d,%s,%s,%s", hr, mins, sec, status, lat, ns, lng, ew, gs, trueCourse, dd, mm, yy, magVar, mvEW, mode)
} else {
msg = fmt.Sprintf("GPRMC,,%s,,,,,,,%02d%02d%02d,%s,%s,%s", status, dd, mm, yy, magVar, mvEW, mode) // return null lat-lng and velocity if invalid GPS
}

var checksum byte
for i := range msg {
checksum = checksum ^ byte(msg[i])
msg = fmt.Sprintf("$GPRMC,,%s,,,,,,,%02d%02d%02d,%s,%s,%s", status, dd, mm, yy, magVar, mvEW, mode) // return null lat-lng and velocity if invalid GPS
}
msg = fmt.Sprintf("$%s*%X\r\n", msg, checksum)
msg = appendNmeaChecksum(msg)
msg += "\r\n"
return msg
}

Expand Down Expand Up @@ -394,27 +390,21 @@ func makeGPGGAString() string {
var msg string

if isGPSValid() {
msg = fmt.Sprintf("GPGGA,%02.f%02.f%05.2f,%010.5f,%s,%011.5f,%s,%d,%d,%.2f,%.1f,M,%.1f,M,,", hr, mins, sec, lat, ns, lng, ew, thisSituation.GPSFixQuality, numSV, hdop, alt, geoidSep)
msg = fmt.Sprintf("$GPGGA,%02.f%02.f%05.2f,%010.5f,%s,%011.5f,%s,%d,%d,%.2f,%.1f,M,%.1f,M,,", hr, mins, sec, lat, ns, lng, ew, thisSituation.GPSFixQuality, numSV, hdop, alt, geoidSep)
} else {
msg = fmt.Sprintf("GPGGA,,,,,,0,%d,,,,,,,", numSV)
msg = fmt.Sprintf("$GPGGA,,,,,,0,%d,,,,,,,", numSV)
}

var checksum byte
for i := range msg {
checksum = checksum ^ byte(msg[i])
}
msg = fmt.Sprintf("$%s*%X\r\n", msg, checksum)
msg = appendNmeaChecksum(msg)
msg += "\r\n"
return msg

}

func makePGRMZString() string {
msg := fmt.Sprintf("PGRMZ,%d,f,3", int(mySituation.BaroPressureAltitude))
var checksum byte
for i := range msg {
checksum = checksum ^ byte(msg[i])
}
msg = fmt.Sprintf("$%s*%X\r\n", msg, checksum)
msg := fmt.Sprintf("$PGRMZ,%d,f,3", int(mySituation.BaroPressureAltitude))
msg = appendNmeaChecksum(msg)
msg += "\r\n"
return msg
}

Expand Down
16 changes: 11 additions & 5 deletions main/gps.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -546,8 +546,8 @@ func configureOgnTracker() {
}

gpsTimeOffsetPpsMs = 200 * time.Millisecond
serialPort.Write([]byte("$POGNS,NavRate=5\r\n")) // Also force NavRate directly, just to make sure it's always set
serialPort.Write([]byte("$POGNS\r\n")) // query current configuration
serialPort.Write([]byte(appendNmeaChecksum("$POGNS,NavRate=5") + "\r\n")) // Also force NavRate directly, just to make sure it's always set
serialPort.Write([]byte(getOgnTrackerConfigQueryString())) // query current configuration

// Configuration for OGN Tracker T-Beam is similar to normal Ublox config, but

Expand Down Expand Up @@ -1698,7 +1698,13 @@ func processNMEALine(l string) (sentenceUsed bool) {
}

func getOgnTrackerConfigString() string {
return fmt.Sprintf("$POGNS,Address=0x%s,AddrType=%d,AcftType=%d,Pilot=%s", globalSettings.OGNAddr, globalSettings.OGNAddrType, globalSettings.OGNAcftType, globalSettings.OGNPilot)
msg := fmt.Sprintf("$POGNS,Address=0x%s,AddrType=%d,AcftType=%d,Pilot=%s", globalSettings.OGNAddr, globalSettings.OGNAddrType, globalSettings.OGNAcftType, globalSettings.OGNPilot)
msg = appendNmeaChecksum(msg)
return msg + "\r\n"
}

func getOgnTrackerConfigQueryString() string {
return appendNmeaChecksum("$POGNS") + "\r\n"
}

func configureOgnTrackerFromSettings() {
Expand All @@ -1709,8 +1715,8 @@ func configureOgnTrackerFromSettings() {
cfg := getOgnTrackerConfigString()
log.Printf("Configuring OGN Tracker: " + cfg)

serialPort.Write([]byte(cfg + "\r\n"))
serialPort.Write([]byte("$POGNS\r\n")) // re-read settings from tracker
serialPort.Write([]byte(getOgnTrackerConfigString()))
serialPort.Write([]byte(getOgnTrackerConfigQueryString())) // re-read settings from tracker
serialPort.Flush()
}

Expand Down
5 changes: 4 additions & 1 deletion main/ogn.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,10 @@ type OgnMessage struct {

func ognPublishNmea(nmea string) {
if globalStatus.OGN_connected {
ognOutgoingMsgChan <- nmea + "\r\n"
if !strings.HasSuffix(nmea, "\r\n") {
nmea += "\r\n"
}
ognOutgoingMsgChan <- nmea
}
}

Expand Down

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