Add support for DDC mode (over I2C)

Author: sandeepmistry

keywords.txt

@@ -31,3 +31,6 @@ wakeup	KEYWORD2
 ########################################
 # Constants
 ########################################
+
+GPS_MODE_UART	LITERAL1
+GPS_MODE_I2C	LITERAL1

src/GPS.cpp

@@ -30,9 +30,11 @@ extern "C" {
 #define GPS_MASK_RMC 0x01
 #define GPS_MASK_GGA 0x02
 
-GPSClass::GPSClass(HardwareSerial& serial, unsigned long baudrate, int extintPin) :
+GPSClass::GPSClass(HardwareSerial& serial, unsigned long baudrate, SerialDDC& serialDDC, unsigned long clockrate, int extintPin) :
   _serial(&serial),
   _baudrate(baudrate),
+  _serialDDC(&serialDDC),
+  _clockRate(clockrate),
   _extintPin(extintPin)
 {
 }
@@ -41,12 +43,26 @@ GPSClass::~GPSClass()
 {
 }
 
-int GPSClass::begin()
+int GPSClass::begin(int mode)
 {
+  _mode = mode;
+
   pinMode(_extintPin, OUTPUT);
   digitalWrite(_extintPin, HIGH);
+  delay(100); // delay for GPS to wakeup
+
+  if (_mode == GPS_MODE_UART) {
+    _serial->begin(_baudrate);
+    _stream = _serial;
+  } else {
+    if (!_serialDDC->begin(_clockRate)) {
+      end();
 
-  _serial->begin(_baudrate);
+      return 0;
+    }
+
+    _stream = _serialDDC;
+  }
 
   _available = 0;
   _index = 0;
@@ -56,10 +72,14 @@ int GPSClass::begin()
 
 void GPSClass::end()
 {
-  _serial->end();
-
   digitalWrite(_extintPin, LOW);
   pinMode(_extintPin, INPUT);
+
+  if (_mode == GPS_MODE_UART) {
+    _serial->end();
+  } else {
+    _serialDDC->end();
+  }
 }
 
 int GPSClass::available()
@@ -143,7 +163,12 @@ void GPSClass::standby()
 
   sendUbx(0x06, 0x3b, payload, sizeof(payload));
 
-  _serial->end();
+  if (_mode == GPS_MODE_UART) {
+    _serial->end();
+  } else {
+    _serialDDC->end();
+  }
+
   digitalWrite(_extintPin, LOW);
 
   _available = 0;
@@ -152,18 +177,23 @@ void GPSClass::standby()
 
 void GPSClass::wakeup()
 {
-  _serial->begin(_baudrate);
-
   digitalWrite(_extintPin, HIGH);
+  delay(100); // delay for GPS to wakeup
+
+  if (_mode == GPS_MODE_UART) {
+    _serial->begin(_baudrate);
+  } else {
+    _serialDDC->begin(_clockRate);
+  }
 
   _available = 0;
   _index = 0;
 }
 
 void GPSClass::poll()
 {
-  if (_serial->available()) {
-    char c = _serial->read();
+  if (_stream->available()) {
+    char c = _stream->read();
 
 #ifdef GPS_DEBUG
     Serial.print(c);
@@ -232,27 +262,29 @@ void GPSClass::sendUbx(uint8_t cls, uint8_t id, uint8_t payload[], uint16_t leng
 {
   uint8_t ckA = 0;
   uint8_t ckB = 0;
-  uint8_t prefix[] = { cls, id, (uint8_t)(length & 0xff), (uint8_t)(length >> 8) };
 
-  for (unsigned int i = 0; i < sizeof(prefix); i++) {
-    ckA += prefix[i];
-    ckB += ckA;
-  }
+  unsigned int cmdLength = 8 + length;
+  uint8_t cmd[cmdLength];
 
-  for (unsigned int i = 0; i < length; i++) {
-    ckA += payload[i];
+  cmd[0] = 0xb5;
+  cmd[1] = 0x62;
+  cmd[2] = cls;
+  cmd[3] = id;
+  cmd[4] = (length & 0xff);
+  cmd[5] = (length >> 8);
+  memcpy(&cmd[6], payload, length);
+
+  // calculate checksum, start at index 2 and up to the payload
+  for (unsigned int i = 2; i < (cmdLength - 2); i++) {
+    ckA += cmd[i];
     ckB += ckA;
   }
 
-  _serial->write(0xb5);
-  _serial->write(0x62);
-  _serial->write(cls);
-  _serial->write(id);
-  _serial->write((uint8_t*)&length, sizeof(length));
-  _serial->write(payload, length);
-  _serial->write(ckA);
-  _serial->write(ckB);
-  _serial->flush();
+  cmd[cmdLength - 2] = ckA;
+  cmd[cmdLength - 1] = ckB;
+
+  _stream->write(cmd, cmdLength);
+  _stream->flush();
 }
 
 float GPSClass::toDegrees(float f)
@@ -263,4 +295,5 @@ float GPSClass::toDegrees(float f)
   return (degrees + (minutes / 60.0));
 }
 
-GPSClass GPS(Serial1, 9600, 7);
+static SerialDDC serialDDC(Wire, 0x42, 0xfd, 0xff);
+GPSClass GPS(Serial1, 9600, serialDDC, 400000, 7);

src/GPS.h

@@ -22,12 +22,20 @@
 
 #include <Arduino.h>
 
+#include "utility/SerialDDC.h"
+
+enum
+{
+  GPS_MODE_UART,
+  GPS_MODE_I2C,
+};
+
 class GPSClass {
 public:
-  GPSClass(HardwareSerial& serial, unsigned long baudrate, int extintPin);
+  GPSClass(HardwareSerial& serial, unsigned long baudrate, SerialDDC& serialDDC, unsigned long clockrate, int extintPin);
   virtual ~GPSClass();
 
-  int begin();
+  int begin(int mode = GPS_MODE_I2C);
   void end();
 
   int available();
@@ -55,8 +63,15 @@ class GPSClass {
 private:
   HardwareSerial* _serial;
   unsigned long _baudrate;
+
+  SerialDDC* _serialDDC;
+  unsigned long _clockRate;
+
   int _extintPin;
 
+  int _mode;
+  Stream* _stream;
+
   int _available;
   char _buffer[82 + 1];
   int _index;

src/utility/SerialDDC.cpp

@@ -0,0 +1,134 @@
+/*
+  This file is part of the Arduino_MKRGPS library.
+  Copyright (c) 2019 Arduino SA. All rights reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include "SerialDDC.h"
+
+SerialDDC::SerialDDC(TwoWire& wire, int address, uint8_t availableRegister, uint8_t readRegister) :
+  _wire(&wire),
+  _address(address),
+  _availableRegister(availableRegister),
+  _readRegister(readRegister)
+{
+}
+
+SerialDDC::~SerialDDC()
+{
+}
+
+int SerialDDC::begin(uint32_t clockFrequency)
+{
+  _wire->begin();
+  _wire->setClock(clockFrequency);
+
+  _wire->beginTransmission(_address);
+  if (_wire->endTransmission() != 0) {
+    // failure
+    end();
+
+    return 0;
+  }
+
+  return 1;
+}
+
+void SerialDDC::end()
+{
+  _wire->end();
+}
+
+int SerialDDC::available()
+{
+  int avail = _wire->available();
+
+  if (avail) {
+    return avail;
+  }
+
+  _wire->beginTransmission(_address);
+  _wire->write(_availableRegister);
+  if (_wire->endTransmission(false) != 0) {
+    return 0;
+  }
+
+  if (_wire->requestFrom(_address, 2) != 2) {
+    return 0;
+  }
+
+  uint8_t availableHigh = _wire->read();
+  uint8_t availableLow  = _wire->read();
+
+  if (availableHigh == 0xff && availableLow == 0xff) {
+    return 0;
+  }
+
+  avail = (availableHigh << 8) | availableLow;
+
+  if (avail > 255) {
+    avail = 255;
+  }
+
+  _wire->beginTransmission(_address);
+  _wire->write(_readRegister);
+  if (_wire->endTransmission(false) != 0) {
+    return 0;
+  }
+
+  if (_wire->requestFrom(_address, avail) != avail) {
+    return 0;
+  }
+
+  return _wire->available();
+}
+
+int SerialDDC::read()
+{
+  return _wire->read();
+}
+
+int SerialDDC::peek()
+{
+  return _wire->peek();
+}
+
+size_t SerialDDC::write(uint8_t b)
+{
+  return write(&b, sizeof(b));
+}
+
+size_t SerialDDC::write(const uint8_t *buffer, size_t size)
+{
+  if (size < 2) {
+    return 0;
+  }
+
+  int result;
+
+  _wire->beginTransmission(_address);
+  result = _wire->write(buffer, size);
+  if (_wire->endTransmission() != 0) {
+    return 0;
+  }
+
+  return result;
+}
+
+void SerialDDC::flush()
+{
+  // no-op
+}

src/utility/SerialDDC.h

@@ -0,0 +1,52 @@
+/*
+  This file is part of the Arduino_MKRGPS library.
+  Copyright (c) 2019 Arduino SA. All rights reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef _SERIAL_DDC_H_
+#define _SERIAL_DDC_H_
+
+#include <Arduino.h>
+
+#include <Wire.h>
+
+class SerialDDC : public Stream {
+public:
+  SerialDDC(TwoWire& wire, int address, uint8_t availableRegister, uint8_t readRegister);
+  virtual ~SerialDDC();
+
+  int begin(uint32_t clockFrequency);
+  void end();
+
+  // from Stream
+  virtual int available();
+  virtual int read();
+  virtual int peek();
+
+  // from Print
+  virtual size_t write(uint8_t);
+  virtual size_t write(const uint8_t *buffer, size_t size);
+  virtual void flush();
+
+private:
+  TwoWire* _wire;
+  int _address;
+  uint8_t _availableRegister;
+  uint8_t _readRegister;
+};
+
+#endif