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+ replace digital read with faster (~3x) code

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=> smaller footprint
  => more robust for low MHz devices
This commit is contained in:
rob tillaart 2014-10-05 10:52:52 +02:00
parent 51a730b10f
commit e4ad65003b
2 changed files with 30 additions and 22 deletions
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42
libraries/DHTlib/dht.cpp
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@ -1,11 +1,12 @@
//
// FILE: dht.cpp
// AUTHOR: Rob Tillaart
// VERSION: 0.1.13
// VERSION: 0.1.14
// PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
// URL: http://arduino.cc/playground/Main/DHTLib
//
// HISTORY:
// 0.1.14 replace digital read with faster (~3x) code => more robust low MHz machines.
// 0.1.13 fix negative temperature
// 0.1.12 support DHT33 and DHT44 initial version
// 0.1.11 renamed DHTLIB_TIMEOUT
@ -19,7 +20,7 @@
// 0.1.03 added error values for temp and humidity when read failed
// 0.1.02 added error codes
// 0.1.01 added support for Arduino 1.0, fixed typos (31/12/2011)
// 0.1.0 by Rob Tillaart (01/04/2011)
// 0.1.00 by Rob Tillaart (01/04/2011)
//
// inspired by DHT11 library
//
@ -107,45 +108,52 @@ int dht::_readSensor(uint8_t pin, uint8_t wakeupDelay)
uint8_t mask = 128;
uint8_t idx = 0;
// replace digitalRead() with Direct Port Reads.
// reduces footprint ~100 bytes => portability issue?
// direct port read is about 3x faster
uint8_t bit = digitalPinToBitMask(pin);
uint8_t port = digitalPinToPort(pin);
volatile uint8_t *PIR = portInputRegister(port);
// EMPTY BUFFER
for (uint8_t i = 0; i < 5; i++) bits[i] = 0;
// REQUEST SAMPLE
pinMode(pin, OUTPUT);
digitalWrite(pin, LOW);
digitalWrite(pin, LOW); // T-be
delay(wakeupDelay);
digitalWrite(pin, HIGH);
digitalWrite(pin, HIGH); // T-go
delayMicroseconds(40);
pinMode(pin, INPUT);
// GET ACKNOWLEDGE or TIMEOUT
uint16_t loopCnt = DHTLIB_TIMEOUT;
while(digitalRead(pin) == LOW)
uint16_t loopCntLOW = DHTLIB_TIMEOUT;
while ((*PIR & bit) == LOW ) // T-rel
{
if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
if (--loopCntLOW == 0) return DHTLIB_ERROR_TIMEOUT;
}
loopCnt = DHTLIB_TIMEOUT;
while(digitalRead(pin) == HIGH)
uint16_t loopCntHIGH = DHTLIB_TIMEOUT;
while ((*PIR & bit) != LOW ) // T-reh
{
if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
if (--loopCntHIGH == 0) return DHTLIB_ERROR_TIMEOUT;
}
// READ THE OUTPUT - 40 BITS => 5 BYTES
for (uint8_t i = 40; i != 0; i--)
{
loopCnt = DHTLIB_TIMEOUT;
while(digitalRead(pin) == LOW)
loopCntLOW = DHTLIB_TIMEOUT;
while ((*PIR & bit) == LOW )
{
if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
if (--loopCntLOW == 0) return DHTLIB_ERROR_TIMEOUT;
}
uint32_t t = micros();
loopCnt = DHTLIB_TIMEOUT;
while(digitalRead(pin) == HIGH)
loopCntHIGH = DHTLIB_TIMEOUT;
while ((*PIR & bit) != LOW )
{
if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
if (--loopCntHIGH == 0) return DHTLIB_ERROR_TIMEOUT;
}
if ((micros() - t) > 40)

10
libraries/DHTlib/dht.h
View File

@ -1,7 +1,7 @@
//
// FILE: dht.h
// AUTHOR: Rob Tillaart
// VERSION: 0.1.13
// VERSION: 0.1.14
// PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
// URL: http://arduino.cc/playground/Main/DHTLib
//
@ -18,7 +18,7 @@
#include <Arduino.h>
#endif
#define DHT_LIB_VERSION "0.1.13"
#define DHT_LIB_VERSION "0.1.14"
#define DHTLIB_OK 0
#define DHTLIB_ERROR_CHECKSUM -1
@ -28,9 +28,9 @@
#define DHTLIB_DHT11_WAKEUP 18
#define DHTLIB_DHT_WAKEUP 1
// max timeout is 100usec.
// For a 16Mhz proc that is max 1600 clock cycles
// loops using TIMEOUT use at least 4 clock cycli
// max timeout is 100 usec.
// For a 16 Mhz proc 100 usec is 1600 clock cycles
// loops using DHTLIB_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 DHTLIB_TIMEOUT (F_CPU/40000)