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gps: improvements and bugfixes (#186)

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* gps: buxfixes and refactoring of API to separate device from parser

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

* gps: simplify time parser

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

* gps: add support for RMC sentences

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

* gps: small renaming to remove reduntant use of word GPS

Signed-off-by: deadprogram <ron@hybridgroup.com>
This commit is contained in:
Ron Evans
2020-08-20 11:22:07 +02:00
committed by GitHub
parent 88aeec9f69
commit 5df96c8138
6 changed files with 174 additions and 107 deletions
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gps/gps.go
+30 -20
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@@ -3,13 +3,19 @@ package gps // import "tinygo.org/x/drivers/gps"
import (
"encoding/hex"
"errors"
"machine"
"strings"
"time"
)
var (
errInvalidNMEASentenceLength = errors.New("invalid NMEA sentence length")
errInvalidNMEAChecksum = errors.New("invalid NMEA sentence checksum")
)
// Device wraps a connection to a GPS device.
type GPSDevice struct {
type Device struct {
buffer []byte
bufIdx int
sentence strings.Builder
@@ -19,8 +25,8 @@ type GPSDevice struct {
}
// NewUART creates a new UART GPS connection. The UART must already be configured.
func NewUART(uart *machine.UART) GPSDevice {
return GPSDevice{
func NewUART(uart *machine.UART) Device {
return Device{
uart: uart,
buffer: make([]byte, bufferSize),
bufIdx: bufferSize,
@@ -29,8 +35,8 @@ func NewUART(uart *machine.UART) GPSDevice {
}
// NewI2C creates a new I2C GPS connection.
func NewI2C(bus *machine.I2C) GPSDevice {
return GPSDevice{
func NewI2C(bus *machine.I2C) Device {
return Device{
bus: bus,
address: I2C_ADDRESS,
buffer: make([]byte, bufferSize),
@@ -39,17 +45,17 @@ func NewI2C(bus *machine.I2C) GPSDevice {
}
}
// ReadNextSentence returns the next valid NMEA sentence from the GPS device.
func (gps *GPSDevice) NextSentence() (sentence string) {
// NextSentence returns the next valid NMEA sentence from the GPS device.
func (gps *Device) NextSentence() (sentence string, err error) {
sentence = gps.readNextSentence()
for !validSentence(sentence) {
sentence = gps.readNextSentence()
if err = validSentence(sentence); err != nil {
return "", err
}
return sentence
return sentence, nil
}
// readNextSentence returns the next sentence from the GPS device.
func (gps *GPSDevice) readNextSentence() (sentence string) {
func (gps *Device) readNextSentence() (sentence string) {
gps.sentence.Reset()
var b byte = ' '
@@ -69,7 +75,7 @@ func (gps *GPSDevice) readNextSentence() (sentence string) {
return sentence
}
func (gps *GPSDevice) readNextByte() (b byte) {
func (gps *Device) readNextByte() (b byte) {
gps.bufIdx += 1
if gps.bufIdx >= bufferSize {
gps.fillBuffer()
@@ -77,7 +83,7 @@ func (gps *GPSDevice) readNextByte() (b byte) {
return gps.buffer[gps.bufIdx]
}
func (gps *GPSDevice) fillBuffer() {
func (gps *Device) fillBuffer() {
if gps.uart != nil {
gps.uartFillBuffer()
} else {
@@ -85,7 +91,7 @@ func (gps *GPSDevice) fillBuffer() {
}
}
func (gps *GPSDevice) uartFillBuffer() {
func (gps *Device) uartFillBuffer() {
for gps.uart.Buffered() < bufferSize {
time.Sleep(100 * time.Millisecond)
}
@@ -93,7 +99,7 @@ func (gps *GPSDevice) uartFillBuffer() {
gps.bufIdx = 0
}
func (gps *GPSDevice) i2cFillBuffer() {
func (gps *Device) i2cFillBuffer() {
for gps.available() < bufferSize {
time.Sleep(100 * time.Millisecond)
}
@@ -102,7 +108,7 @@ func (gps *GPSDevice) i2cFillBuffer() {
}
// Available returns how many bytes of GPS data are currently available.
func (gps *GPSDevice) available() (available int) {
func (gps *Device) available() (available int) {
var lengthBytes [2]byte
gps.bus.Tx(gps.address, []byte{BYTES_AVAIL_REG}, lengthBytes[0:2])
available = int(lengthBytes[0])*256 + int(lengthBytes[1])
@@ -110,7 +116,7 @@ func (gps *GPSDevice) available() (available int) {
}
// WriteBytes sends data/commands to the GPS device
func (gps *GPSDevice) WriteBytes(bytes []byte) {
func (gps *Device) WriteBytes(bytes []byte) {
if gps.uart != nil {
gps.uart.Write(bytes)
} else {
@@ -119,14 +125,18 @@ func (gps *GPSDevice) WriteBytes(bytes []byte) {
}
// validSentence checks if a sentence has been received uncorrupted
func validSentence(sentence string) bool {
func validSentence(sentence string) error {
if len(sentence) < 4 || sentence[0] != '$' || sentence[len(sentence)-3] != '*' {
return false
return errInvalidNMEASentenceLength
}
var cs byte = 0
for i := 1; i < len(sentence)-3; i++ {
cs ^= sentence[i]
}
checksum := hex.EncodeToString([]byte{cs})
return (checksum[0] == sentence[len(sentence)-2]) && (checksum[1] == sentence[len(sentence)-1])
if (checksum[0] != sentence[len(sentence)-2]) || (checksum[1] != sentence[len(sentence)-1]) {
return errInvalidNMEAChecksum
}
return nil
}