func (w *WeatherStation) getDataWithCRC16(numBytes int64, prompt string) ([]byte, error) {
var err error
buf := new(bytes.Buffer)
if prompt != "" {
// We'll write to a Buffer and then dump it to the device
_, err = buf.WriteString(prompt)
if err != nil {
return nil, err
}
// Write the buffer to the device
_, err = buf.WriteTo(w.RW)
if err != nil {
return nil, err
}
w.RW.Flush()
}
// We're going to try reading data from the device maxTries times...
for i := 1; i <= maxTries; i++ {
// If it's not our first attempt at reading from the console, we send a RESEND command
// to goad the console into responding.
if i > 1 {
_, err = buf.Write([]byte(RESEND))
if err != nil {
log.Println("Could not write RESEND command to buffer")
return nil, err
}
// Write the buffer to the console
_, err = buf.WriteTo(w.RW)
if err != nil {
log.Println("Could not write buffer to console")
return nil, err
}
checkBytes := make([]byte, numBytes)
_, err := w.RW.Read(checkBytes)
if err != nil {
return nil, err
}
// Do a CRC16 check on data we read and return data if it passes
if crc16.Crc16(checkBytes) == uint16(0) {
return checkBytes, nil
}
// We didn't pass the CRC check so we loop again.
log.Println("The data read did not pass the CRC16 check")
}
}
// We failed at reading data from the console
return nil, fmt.Errorf("Failed to read any data from the console after %v attempts.", maxTries)
}
func (w *WeatherStation) sendDataWithCRC16(d []byte) error {
var resp []byte
// We'll write to a Buffer and then dump the buffer to the device
buf := new(bytes.Buffer)
check := crc16.Crc16(d)
// First, write the data
_, err := buf.Write(d)
if err != nil {
return err
}
// Next, write the CRC in big-endian order
err = binary.Write(buf, binary.BigEndian, check)
if err != nil {
return err
}
for i := 0; i <= maxTries; i++ {
_, err := buf.WriteTo(w.RW)
if err != nil {
return err
}
_, err = w.RW.Read(resp)
if err != nil {
log.Println("Error reading response:", err)
return err
}
if resp[0] != ACK[0] {
log.Println("No <ACK> was received from console")
return nil
}
}
return fmt.Errorf("I/O error writing data with CRC to device.")
}
// GetDavisLoopPackets attempts to initiate a LOOP command against the station and retrieve some packets
func (w *WeatherStation) GetDavisLoopPackets(n int, packetChan chan<- Reading) error {
// Make a slice of loop packet maps, n elements long.
//var loopPackets []*LoopPacketWithTrend
log.Println("Initiating LOOP mode for", n, "packets.")
// Request n packets
w.sendData([]byte(fmt.Sprintf("LOOP %v\n", n)))
w.RW.Flush()
time.Sleep(1 * time.Second)
tries := 1
for l := 0; l < n; l++ {
time.Sleep(1 * time.Second)
if tries > maxTries {
log.Println("Max retries exeeded while getting loop data")
return nil
}
err := w.C.SetReadDeadline(time.Now().Add(5 * time.Second))
if err != nil {
log.Println("Error setting read deadline:", err)
}
// Read 99 bytes from the console
buf := make([]byte, 99)
_, err = w.RW.Read(buf)
//_, err = io.ReadAtLeast(w.C, buf, 99)
if err != nil {
tries++
log.Printf("Error while reading from console, LOOP %v: %v", l, err)
return nil
}
if buf[95] != 0x0A && buf[96] != 0x0D {
log.Println("End-of-packet signature not found; rejecting.")
} else {
if crc16.Crc16(buf) != 0 {
log.Printf("LOOP %v CRC error. Try #%v", l, tries)
tries++
continue
}
unpacked, err := w.unpackLoopPacket(buf)
if err != nil {
tries++
log.Printf("Error unpacking loop packet: %v. Try %v", err, tries)
continue
}
tries = 1
r := convValues(unpacked)
// Set the timestamp on our reading to the current system time
r.Timestamp = time.Now()
r.StationName = w.Config.Device.Name
packetChan <- r
//loopPackets = append(loopPackets, unpacked)
}
}
return nil
}
