optimized wakeup and timeout

Author: RobTillaart

libraries/DHTlib/dht.cpp

@@ -1,11 +1,12 @@
 //
 // FILE: dht.cpp
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.09
+// VERSION: 0.1.10
 // PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
 // URL: http://arduino.cc/playground/Main/DHTLib
 //
 // HISTORY:
+// 0.1.10 optimized faster WAKEUP + TIMEOUT
 // 0.1.09 optimize size: timeout check + use of mask
 // 0.1.08 added formula for timeout based upon clockspeed
 // 0.1.07 added support for DHT21
@@ -24,13 +25,12 @@
 
 #include "dht.h"
 
-// #define TIMEOUT 10000
-// uint16_t for UNO, higher CPU speeds => exceed MAXINT.
-// works for DUE
-// 16 MHz => 10000
-// 84 MHz => 52500
-// 100MHz => 62500
-#define TIMEOUT (F_CPU/1600)
+// max timeout is 100usec.
+// For a 16Mhz proc that is max 1600 clock cycles
+// loops using TIMEOUT use at least 4 clock cycli
+// so 100 us takes max 400 loops
+// so by dividing F_CPU by 40000 we "fail" as fast as possible
+#define TIMEOUT (F_CPU/40000)
 
 
 /////////////////////////////////////////////////////
@@ -45,7 +45,7 @@
 int dht::read11(uint8_t pin)
 {
  // READ VALUES
- int rv = read(pin);
+ int rv = read(pin, DHTLIB_DHT11_WAKEUP);
  if (rv != DHTLIB_OK)
  {
  humidity = DHTLIB_INVALID_VALUE; // invalid value, or is NaN prefered?
@@ -71,7 +71,8 @@ int dht::read11(uint8_t pin)
 // DHTLIB_ERROR_TIMEOUT
 int dht::read21(uint8_t pin)
 {
- return read22(pin); // dataformat identical to DHT22
+ // dataformat & wakeup identical to DHT22
+ return read22(pin);
 }
 
 // return values:
@@ -81,7 +82,7 @@ int dht::read21(uint8_t pin)
 int dht::read22(uint8_t pin)
 {
  // READ VALUES
- int rv = read(pin);
+ int rv = read(pin, DHTLIB_DHT22_WAKEUP);
  if (rv != DHTLIB_OK)
  {
  humidity = DHTLIB_INVALID_VALUE; // invalid value, or is NaN prefered?
@@ -116,44 +117,52 @@ int dht::read22(uint8_t pin)
 // return values:
 // DHTLIB_OK
 // DHTLIB_ERROR_TIMEOUT
-int dht::read(uint8_t pin)
+int dht::read(uint8_t pin, uint8_t wakeupDelay)
 {
  // INIT BUFFERVAR TO RECEIVE DATA
  uint8_t mask = 128;
  uint8_t idx = 0;
 
  // EMPTY BUFFER
- for (uint8_t i=0; i< 5; i++) bits[i] = 0;
+ for (uint8_t i = 0; i < 5; i++) bits[i] = 0;
 
  // REQUEST SAMPLE
  pinMode(pin, OUTPUT);
  digitalWrite(pin, LOW);
- delay(20);
+ delay(wakeupDelay);
  digitalWrite(pin, HIGH);
  delayMicroseconds(40);
  pinMode(pin, INPUT);
 
  // GET ACKNOWLEDGE or TIMEOUT
  unsigned int loopCnt = TIMEOUT;
  while(digitalRead(pin) == LOW)
- if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ {
+ if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ }
 
  loopCnt = TIMEOUT;
  while(digitalRead(pin) == HIGH)
- if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ {
+ if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ }
 
  // READ THE OUTPUT - 40 BITS => 5 BYTES
- for (uint8_t i=0; i<40; i++)
+ for (uint8_t i = 0; i < 40; i++)
  {
  loopCnt = TIMEOUT;
  while(digitalRead(pin) == LOW)
- if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ {
+ if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ }
 
  unsigned long t = micros();
 
  loopCnt = TIMEOUT;
  while(digitalRead(pin) == HIGH)
- if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ {
+ if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
+ }
 
  if ((micros() - t) > 40) bits[idx] |= mask;
  mask >>= 1;
@@ -163,7 +172,6 @@ int dht::read(uint8_t pin)
  idx++;
  }
  }
-
  return DHTLIB_OK;
 }
 //

libraries/DHTlib/dht.h

@@ -1,7 +1,7 @@
 //
 // FILE: dht.h
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.09
+// VERSION: 0.1.10
 // PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
 // URL: http://arduino.cc/playground/Main/DHTLib
 //
@@ -18,12 +18,16 @@
 #include <Arduino.h>
 #endif
 
-#define DHT_LIB_VERSION "0.1.09"
+#define DHT_LIB_VERSION "0.1.10"
+
+#define DHTLIB_OK 0
+#define DHTLIB_ERROR_CHECKSUM -1
+#define DHTLIB_ERROR_TIMEOUT -2
+#define DHTLIB_INVALID_VALUE -999
+
+#define DHTLIB_DHT11_WAKEUP 18
+#define DHTLIB_DHT22_WAKEUP 1
 
-#define DHTLIB_OK0
-#define DHTLIB_ERROR_CHECKSUM-1
-#define DHTLIB_ERROR_TIMEOUT-2
-#define DHTLIB_INVALID_VALUE-999
 
 class dht
 {
@@ -37,7 +41,7 @@ class dht
 
 private:
  uint8_t bits[5]; // buffer to receive data
- int read(uint8_t pin);
+ int read(uint8_t pin, uint8_t wakeupDelay);
 };
 #endif
 //