Using 1-Wire device with Intel Galileo

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Many people have had trouble with getting 1-Wire devices to work with the Galileo and Galileo Gen2 boards.

The main reason is that the Galileo and Galileo Gen2 uses IO expanders for many of  its GPIOs. Even with the pins Arduno header pins that have native SoC IO speeds, it is not possible because the GPIOs that control the muxing of those pins uses pins from the IO expanders.

Galileo Muxing For Pin2

Galileo Cypress IO Expander

If we look at the two images taken form the Galileo schematic, IO which is connected to the Arduino Digital 2 pin, is controlled by a mux pin IO2_MUX. This pin is then connected to the Cypress IO expander.

The end result is there is significant latency when switching pin direction using pinMode() becuase it requires I2C transactions with the IO expanders.

I will show a way to use 1-Wire device with the Galileo and Galileo Gen2 boards.

The trick is to use 2 pins instead of 1. For the Galileo, pins 2 and 3 must be used since they are the only pins fast enough to achieve this. For the Galileo Gen2, any pins except pins 7 and 8 can be used.

For this tutorial, I will use a DHT11 sensor which a very cheap and popular 1-Wire humidity and temperature sensor.

The Proper Way

The proper way of doing this is to use a tri-state buffer.

This works because, when pin 3 is pulled HIGH, the tri-state buffer prevents the HIGH signal from being passed to the other side. However, the 1-Wire device still sees a high signal because of the pull-up resistor.
When pin 3 is pulled LOW, the signal passes through the tri-state buffer and a LOW signal is detected by the 1-Wire device.

The Easy Way

For the easy way the only extra hardware needed is a diode such as the 1N4148 signal diode. This essential works the same way as the tri-state buffer method where only a LOW signal passes through because current only passes in one direction through a diode.

Since we are now using two pins, we will also need to make changes in the libraries used. As an example, I modified the DHT-11 library from Adafruit.

 1 #ifndef DHT_H
 2 #define DHT_H
 3 #if ARDUINO >= 100
 4  #include "Arduino.h"
 5 #else
 6  #include "WProgram.h"
 7 #endif
 8
 9 /* DHT library
10
11 MIT license
12 written by Adafruit Industries
13
14 Modified by Dino Tinitigan ([email protected] to work on Intel Galileo boards
15 */
16
17 // how many timing transitions we need to keep track of. 2 * number bits + extra
18 #define MAXTIMINGS 85
19
20 #define DHT11 11
21 #define DHT22 22
22 #define DHT21 21
23 #define AM2301 21
24
25 class DHT {
26  private:
27  uint8_t data[6];
28  uint8_t _inpin, _outpin, _type, _count;
29  unsigned long _lastreadtime;
30  boolean firstreading;
31  int pulseLength(int pin);
32  void delayMicrosGal(unsigned long usec);
33  int bitsToByte(int bits[]);
34
35  public:
36  DHT(uint8_t inPin, uint8_t outPin,uint8_t type, uint8_t count=6);
37  void begin(void);
38  float readTemperature(bool S=false);
39  float convertCtoF(float);
40  float computeHeatIndex(float tempFahrenheit, float percentHumidity);
41  float readHumidity(void);
42  boolean read(void);
43
44
45 };
46 #endif

  1 /* DHT library
  2
  3 MIT license
  4 written by Adafruit Industries
  5
  6 Modified by Dino Tinitigan ([email protected] to work on Intel Galileo boards
  7 */
  8
  9
 10 #include "DHT.h"
 11
 12 DHT::DHT(uint8_t inPin, uint8_t outPin, uint8_t type, uint8_t count) {
 13  _inpin = inPin;
 14  _outpin = outPin;
 15  _type = type;
 16  _count = count;
 17  firstreading = true;
 18 }
 19
 20 void DHT::begin(void) {
 21  // set up the pins!
 22  pinMode(_inpin, INPUT);
 23  pinMode(_outpin, INPUT);
 24  digitalWrite(_outpin, HIGH);
 25  _lastreadtime = 0;
 26 }
 27
 28 //boolean S == Scale. True == Farenheit; False == Celcius
 29 float DHT::readTemperature(bool S) {
 30  float f;
 31
 32  if (read()) {
 33  switch (_type) {
 34  case DHT11:
 35  f = data[2];
 36  if(S)
 37  f = convertCtoF(f);
 38
 39  return f;
 40  case DHT22:
 41  case DHT21:
 42  f = data[2] & 0x7F;
 43  f *= 256;
 44  f += data[3];
 45  f /= 10;
 46  if (data[2] & 0x80)
 47  f *= -1;
 48  if(S)
 49  f = convertCtoF(f);
 50
 51  return f;
 52  }
 53  }
 54  return NAN;
 55 }
 56
 57 float DHT::convertCtoF(float c) {
 58  return c * 9 / 5 + 32;
 59 }
 60
 61 float DHT::readHumidity(void) {
 62  float f;
 63  if (read()) {
 64  switch (_type) {
 65  case DHT11:
 66  f = data[0];
 67  return f;
 68  case DHT22:
 69  case DHT21:
 70  f = data[0];
 71  f *= 256;
 72  f += data[1];
 73  f /= 10;
 74  return f;
 75  }
 76  }
 77  return NAN;
 78 }
 79
 80 float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
 81  // Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
 82  // Wikipedia: http://en.wikipedia.org/wiki/Heat_index
 83  return -42.379 +
 84  2.04901523 * tempFahrenheit +
 85  10.14333127 * percentHumidity +
 86  -0.22475541 * tempFahrenheit*percentHumidity +
 87  -0.00683783 * pow(tempFahrenheit, 2) +
 88  -0.05481717 * pow(percentHumidity, 2) +
 89  0.00122874 * pow(tempFahrenheit, 2) * percentHumidity +
 90  0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
 91  -0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
 92 }
 93
 94
 95 boolean DHT::read(void) {
 96  uint8_t laststate = HIGH;
 97  uint8_t counter = 0;
 98  uint8_t j = 0, i;
 99  unsigned long currenttime;
100
101  int bitContainer[8];
102
103  // Check if sensor was read less than two seconds ago and return early
104  // to use last reading.
105  currenttime = millis();
106  if (currenttime < _lastreadtime) {
107  // ie there was a rollover
108  _lastreadtime = 0;
109  }
110  if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
111  return true; // return last correct measurement
112  //delay(2000 - (currenttime - _lastreadtime));
113  }
114  firstreading = false;
115  /*
116  Serial.print("Currtime: "); Serial.print(currenttime);
117  Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
118  */
119  _lastreadtime = millis();
120
121  data[0] = data[1] = data[2] = data[3] = data[4] = 0;
122
123  // pull the pin high and wait 250 milliseconds
124  pinMode(_outpin, OUTPUT_FAST);
125  pinMode(_inpin, INPUT_FAST);
126  digitalWrite(_outpin, HIGH);
127  delay(250);
128
129  // now pull it low for ~20 milliseconds
130  noInterrupts();
131  digitalWrite(_outpin, LOW);
132  delay(20);
133  digitalWrite(_outpin, HIGH);
134  delayMicrosGal(40);
135
136  //read the 40 bits
137  delayMicrosGal(160);
138  for(int bytes = 0; bytes < 5; bytes++)
139  {
140  for(int i = 0; i < 8; i++)
141  {
142  int pulse = pulseLength(_inpin);
143  if(pulse > 30)
144  {
145  bitContainer[i] = 1;
146  }
147  else
148  {
149  bitContainer[i] = 0;
150  }
151  }
152  data[bytes] = bitsToByte(bitContainer);
153  }
154
155  interrupts();
156
157
158  //Serial.println(j, DEC);
159  /**
160  Serial.print(data[0], HEX); Serial.print(", ");
161  Serial.print(data[1], HEX); Serial.print(", ");
162  Serial.print(data[2], HEX); Serial.print(", ");
163  Serial.print(data[3], HEX); Serial.print(", ");
164  Serial.print(data[4], HEX); Serial.print(" =? ");
165  Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
166  **/
167  /**
168  Serial.println(data[0]);
169  Serial.println(data[1]);
170  Serial.println(data[2]);
171  Serial.println(data[3]);
172  Serial.println(data[4]);
173  **/
174  // check we read 40 bits and that the checksum matches
175
176  if((data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)))
177  {
178  return true;
179  }
180
181
182  return false;
183
184 }
185
186 void DHT::delayMicrosGal(unsigned long usec)
187 {
188  unsigned long a = micros();
189  unsigned long b = a;
190  while((b-a) < usec)
191  {
192  b = micros();
193  }
194 }
195
196 int DHT::pulseLength(int pin)
197 {
198  unsigned long a = micros();
199  unsigned long b = a;
200  unsigned long c = a;
201  int timeout = 150;
202  int fastPin = 0;
203  int highValue = 0;
204
205  if(PLATFORM_NAME == "GalileoGen2")
206  {
207  switch(pin)
208  {
209  case 0:
210  fastPin = GPIO_FAST_ID_QUARK_SC(0x08);
211  highValue = 0x08;
212  break;
213  case 1:
214  fastPin = GPIO_FAST_ID_QUARK_SC(0x10);
215  highValue = 0x10;
216  break;
217  case 2:
218  fastPin = GPIO_FAST_ID_QUARK_SC(0x20);
219  highValue = 0x20;
220  break;
221  case 3:
222  fastPin = GPIO_FAST_ID_QUARK_SC(0x40);
223  highValue = 0x40;
224  break;
225  case 4:
226  fastPin = GPIO_FAST_ID_QUARK_NC_RW(0x10);
227  highValue = 0x10;
228  break;
229  case 5:
230  fastPin = GPIO_FAST_ID_QUARK_NC_CW(0x01);
231  highValue = 0x01;
232  break;
233  case 6:
234  fastPin = GPIO_FAST_ID_QUARK_NC_CW(0x02);
235  highValue = 0x02;
236  break;
237  case 9:
238  fastPin = GPIO_FAST_ID_QUARK_NC_RW(0x04);
239  highValue = 0x04;
240  break;
241  case 10:
242  fastPin = GPIO_FAST_ID_QUARK_SC(0x04);
243  highValue = 0x04;
244  break;
245  case 11:
246  fastPin = GPIO_FAST_ID_QUARK_NC_RW(0x08);
247  highValue = 0x08;
248  break;
249  case 12:
250  fastPin = GPIO_FAST_ID_QUARK_SC(0x80);
251  highValue = 0x80;
252  break;
253  case 13:
254  fastPin = GPIO_FAST_ID_QUARK_NC_RW(0x20);
255  highValue = 0x20;
256  break;
257  default:
258  highValue = 1;
259  break;
260  }
261  }
262  else
263  {
264  switch(_inpin)
265  {
266  case 2:
267  fastPin = GPIO_FAST_ID_QUARK_SC(0x40);
268  highValue = 0x40;
269  break;
270  case 3:
271  fastPin = GPIO_FAST_ID_QUARK_SC(0x80);
272  highValue = 0x80;
273  break;
274  default:
275  highValue = 1;
276  break;
277  }
278  }
279  a = micros();
280  while(fastGpioDigitalRead(fastPin) == 0)
281  {
282  b= micros();
283  if((b - a) >= timeout)
284  {
285  break;
286  }
287  }
288  a = micros();
289  while(fastGpioDigitalRead(fastPin) == highValue)
290  {
291  b= micros();
292  if((b - a) >= timeout)
293  {
294  break;
295  }
296  }
297  return (b - a);
298  return 0;
299 }
300
301
302 int DHT::bitsToByte(int bits[])
303 {
304  int data = 0;
305  for(int i = 0; i < 8; i++)
306  {
307  if (bits[i])
308  {
309  data |= (int)(1 << (7 - i));
310  }
311  }
312  return data;
313 }

 1 // Example testing sketch for various DHT humidity/temperature sensors
 2 // Written by ladyada, public domain
 3
 4 #include "DHT.h"
 5
 6 #define DHTIN 2 // what pin we‘re connected to
 7 #define DHTOUT 3
 8
 9 // Uncomment whatever type you‘re using!
10 #define DHTTYPE DHT11 // DHT 11
11 //#define DHTTYPE DHT22 // DHT 22 (AM2302)
12 //#define DHTTYPE DHT21 // DHT 21 (AM2301)
13
14 // Connect pin 1 (on the left) of the sensor to +5V
15 // Connect pin 2 of the sensor to whatever your DHTPIN is
16 // Connect pin 4 (on the right) of the sensor to GROUND
17 // Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
18
19 DHT dht(DHTIN,DHTOUT, DHTTYPE);
20
21 void setup() {
22  Serial.begin(9600);
23  Serial.println("DHTxx test!");
24
25  dht.begin();
26 }
27
28 void loop() {
29  // Wait a few seconds between measurements.
30  delay(2000);
31
32  // Reading temperature or humidity takes about 250 milliseconds!
33  // Sensor readings may also be up to 2 seconds ‘old‘ (its a very slow sensor)
34  float h = dht.readHumidity();
35  // Read temperature as Celsius
36  float t = dht.readTemperature();
37  // Read temperature as Fahrenheit
38  float f = dht.readTemperature(true);
39
40  // Check if any reads failed and exit early (to try again).
41  if (isnan(h) || isnan(t) || isnan(f)) {
42  Serial.println("Failed to read from DHT sensor!");
43  return;
44  }
45
46  // Compute heat index
47  // Must send in temp in Fahrenheit!
48  float hi = dht.computeHeatIndex(f, h);
49
50  Serial.print("Humidity: ");
51  Serial.print(h);
52  Serial.print(" %\t");
53  Serial.print("Temperature: ");
54  Serial.print(t);
55  Serial.print(" *C ");
56  Serial.print(f);
57  Serial.print(" *F\t");
58  Serial.print("Heat index: ");
59  Serial.print(hi);
60  Serial.println(" *F");
61 }

原文地址：http://bigdinotech.com/tutorials/galileo-tutorials/using-1-wire-device-with-intel-galileo/