mhz16: Initial implementation

This library implements support for the MHZ16 CO2 sensor.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Zion Orent <zorent@ics.com>
Signed-off-by: John Van Drasek <john.r.van.drasek@intel.com>

src/mhz16/mhz16.cxx

@@ -0,0 +1,219 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <iostream>
+
+#include "mhz16.h"
+
+using namespace upm;
+using namespace std;
+
+static const int defaultDelay = 100;     // max wait time for read
+
+MHZ16::MHZ16(int uart)
+{
+  m_ttyFd = -1;
+
+  if ( !(m_uart = mraa_uart_init(uart)) )
+    {
+      cerr << __FUNCTION__ << ": mraa_uart_init() failed" << endl;
+      return;
+    }
+
+  // This requires a recent MRAA (1/2015)
+  char *devPath = mraa_uart_get_dev_path(m_uart);
+
+  if (!devPath)
+    {
+      cerr << __FUNCTION__ << ": mraa_uart_get_dev_path() failed" << endl;
+      return;
+    }
+
+  // now open the tty
+  if ( (m_ttyFd = open(devPath, O_RDWR)) == -1)
+    {
+      cerr << __FUNCTION__ << ": open of " << devPath << " failed: " 
+           << strerror(errno) << endl;
+      return;
+    }
+}
+
+MHZ16::~MHZ16()
+{
+  if (m_ttyFd != -1)
+    close(m_ttyFd);
+
+  mraa_deinit();
+}
+
+bool MHZ16::dataAvailable(unsigned int millis)
+{
+  if (m_ttyFd == -1)
+    return false;
+
+  struct timeval timeout;
+
+  // no waiting
+  timeout.tv_sec = 0;
+  timeout.tv_usec = millis * 1000;
+
+  int nfds;  
+  fd_set readfds;
+
+  FD_ZERO(&readfds);
+
+  FD_SET(m_ttyFd, &readfds);
+  
+  if (select(m_ttyFd + 1, &readfds, NULL, NULL, &timeout) > 0)
+    return true;                // data is ready
+  else
+    return false;
+}
+
+int MHZ16::readData(char *buffer, size_t len)
+{
+  if (m_ttyFd == -1)
+    return(-1);
+
+  if (!dataAvailable(defaultDelay))
+    return 0;               // timed out
+
+  int rv = read(m_ttyFd, buffer, len);
+
+  if (rv < 0)
+    cerr << __FUNCTION__ << ": read failed: " << strerror(errno) << endl;
+
+  return rv;
+}
+
+int MHZ16::writeData(char *buffer, size_t len)
+{
+  if (m_ttyFd == -1)
+    return(-1);
+
+  // first, flush any pending but unread input
+  tcflush(m_ttyFd, TCIFLUSH);
+
+  int rv = write(m_ttyFd, buffer, len);
+
+  if (rv < 0)
+    {
+      cerr << __FUNCTION__ << ": write failed: " << strerror(errno) << endl;
+      return rv;
+    }
+
+  tcdrain(m_ttyFd);
+
+  return rv;
+}
+
+bool MHZ16::setupTty(speed_t baud)
+{
+  if (m_ttyFd == -1)
+    return(false);
+  
+  struct termios termio;
+
+  // get current modes
+  tcgetattr(m_ttyFd, &termio);
+
+  // setup for a 'raw' mode.  81N, no echo or special character
+  // handling, such as flow control.
+  cfmakeraw(&termio);
+
+  // set our baud rates
+  cfsetispeed(&termio, baud);
+  cfsetospeed(&termio, baud);
+
+  // make it so
+  if (tcsetattr(m_ttyFd, TCSAFLUSH, &termio) < 0)
+    {
+      cerr << __FUNCTION__ << ": tcsetattr failed: " << strerror(errno) << endl;
+      return false;
+    }
+
+  return true;
+}
+
+bool MHZ16::verifyPacket(unsigned char *pkt)
+{
+  if (pkt[0] != 0xff || pkt[1] != 0x86)
+    {
+      cerr << __FUNCTION__ << ": Inavlid packet header." << endl;
+      return false;
+    }
+  
+  return true;
+}
+
+bool MHZ16::getData(int *gas, int *temp)
+{
+  // the query command
+  const unsigned char cmd[9] = 
+    {0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
+
+  writeData((char *)cmd, 9);
+
+  // wait up to one second for a response
+  if (!dataAvailable(1000))
+    {
+      cerr << __FUNCTION__ << ": Timed out waiting for response." << endl;
+      return false;
+    }
+
+  // read the packet
+  unsigned char packet[9];
+  int rv;
+
+  if ((rv = readData((char *)packet, 9)) != 9)
+    {
+      cerr << __FUNCTION__ << ": Invalid packet read, rv = " << rv 
+           << ", expected 9." << endl;
+      return false;
+    }
+  
+  if (!verifyPacket(packet))
+    {
+      cerr << __FUNCTION__ << ": Packet verify failed." << endl;
+      return false;
+    }
+
+  // pull out the data and return it.
+  *gas = (packet[2] << 8) | packet[3];
+  *temp = packet[4] - 40;
+
+  return true;
+}
+
+void MHZ16::calibrateZeroPoint()
+{
+  // the query command
+  const unsigned char cmd[9] = 
+    {0xff, 0x01, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78};
+
+  writeData((char *)cmd, 9);
+
+  // no response
+}
+