Cause interrupts to be reenabled if a timeout occurs while waiting for the sensor.

This commit is contained in:
Zirientis 2015-07-01 17:53:53 -07:00
parent a1393fc0ff
commit a2208eb813
2 changed files with 58 additions and 46 deletions

93
DHT.cpp
View File

@ -140,62 +140,63 @@ boolean DHT::read(void) {
// Turn off interrupts temporarily because the next sections are timing critical
// and we don't want any interruptions.
noInterrupts();
{
InterruptLock lock;
// End the start signal by setting data line high for 40 microseconds.
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
// End the start signal by setting data line high for 40 microseconds.
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
// Now start reading the data line to get the value from the DHT sensor.
pinMode(_pin, INPUT);
delayMicroseconds(10); // Delay a bit to let sensor pull data line low.
// Now start reading the data line to get the value from the DHT sensor.
pinMode(_pin, INPUT);
delayMicroseconds(10); // Delay a bit to let sensor pull data line low.
// First expect a low signal for ~80 microseconds followed by a high signal
// for ~80 microseconds again.
if (expectPulse(LOW) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse."));
_lastresult = false;
return _lastresult;
}
if (expectPulse(HIGH) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse."));
_lastresult = false;
return _lastresult;
}
// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
// microsecond low pulse followed by a variable length high pulse. If the
// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
// then it's a 1. We measure the cycle count of the initial 50us low pulse
// and use that to compare to the cycle count of the high pulse to determine
// if the bit is a 0 (high state cycle count < low state cycle count), or a
// 1 (high state cycle count > low state cycle count).
for (int i=0; i<40; ++i) {
uint32_t lowCycles = expectPulse(LOW);
if (lowCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit low pulse."));
// First expect a low signal for ~80 microseconds followed by a high signal
// for ~80 microseconds again.
if (expectPulse(LOW) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse."));
_lastresult = false;
return _lastresult;
}
uint32_t highCycles = expectPulse(HIGH);
if (highCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit high pulse."));
if (expectPulse(HIGH) == 0) {
DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse."));
_lastresult = false;
return _lastresult;
}
data[i/8] <<= 1;
// Now compare the low and high cycle times to see if the bit is a 0 or 1.
if (highCycles > lowCycles) {
// High cycles are greater than 50us low cycle count, must be a 1.
data[i/8] |= 1;
}
// Else high cycles are less than (or equal to, a weird case) the 50us low
// cycle count so this must be a zero. Nothing needs to be changed in the
// stored data.
}
// Re-enable interrupts, timing critical code is complete.
interrupts();
// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
// microsecond low pulse followed by a variable length high pulse. If the
// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
// then it's a 1. We measure the cycle count of the initial 50us low pulse
// and use that to compare to the cycle count of the high pulse to determine
// if the bit is a 0 (high state cycle count < low state cycle count), or a
// 1 (high state cycle count > low state cycle count).
for (int i=0; i<40; ++i) {
uint32_t lowCycles = expectPulse(LOW);
if (lowCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit low pulse."));
_lastresult = false;
return _lastresult;
}
uint32_t highCycles = expectPulse(HIGH);
if (highCycles == 0) {
DEBUG_PRINTLN(F("Timeout waiting for bit high pulse."));
_lastresult = false;
return _lastresult;
}
data[i/8] <<= 1;
// Now compare the low and high cycle times to see if the bit is a 0 or 1.
if (highCycles > lowCycles) {
// High cycles are greater than 50us low cycle count, must be a 1.
data[i/8] |= 1;
}
// Else high cycles are less than (or equal to, a weird case) the 50us low
// cycle count so this must be a zero. Nothing needs to be changed in the
// stored data.
}
// Timing critical code is now complete.
}
DEBUG_PRINTLN(F("Received:"));
DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", "));

11
DHT.h
View File

@ -57,4 +57,15 @@ class DHT {
};
class InterruptLock {
public:
InterruptLock() {
noInterrupts();
}
~InterruptLock() {
interrupts();
}
};
#endif