An arduino library to communicate using the Dallas one-wire protocol, where the Arduino takes the role of a slave.
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#include "Arduino.h"
#include "LowLevel.h"
#include "SerialChannel.h"
#define LEDPin 13
#define OWPin 2
#define InterruptNumber 0 // Must correspond to the OWPin to correctly detect state changes. On Arduino Uno, interrupt 0 is for digital pin 2
#define ResetMinDuration 480
#define ResetMaxDuration 900
#define PresenceWaitDuration 30
#define PresenceDuration 300
#define ReadBitSamplingTime 13 // the theorical time is about 30us, but given various overhead, this is the empirical delay I've found works best (on Arduino Uno)
#define SendBitDuration 35
const byte InvalidBit = (byte)-1;
const byte IncompleteBit = (byte)-2;
SerialChannel debug("debug");
Pin owPin(OWPin);
Pin owOutTestPin(3);
Pin led(LEDPin);
enum OwStatus
{
OS_WaitReset,
OS_Presence,
OS_WaitCommand,
OS_SearchRom,
};
OwStatus status;
byte owROM[8] = { 0xE2, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00 };
byte searchROMCurrentByte = 0;
byte searchROMCurrentBit = 0;
bool searchROMSendingInverse = false;
bool searchROMReadingMasterResponseBit = false;
void owPullLow()
{
owPin.outputMode();
owPin.writeLow();
owOutTestPin.writeLow();
}
void owRelease()
{
owPin.inputMode();
owOutTestPin.writeHigh();
}
volatile unsigned long resetStart = (unsigned long)-1;
unsigned long lastReset = (unsigned long)-1;
unsigned long bitStart = (unsigned long)-1;
byte receivingByte = 0;
byte receivingBitPos = 0;
bool searchRomNextBit = false;
bool searchRomNextBitToSend = false;
void setup()
{
owROM[7] = crc8((char*)owROM, 7);
led.outputMode();
owPin.inputMode();
owOutTestPin.outputMode();
owOutTestPin.writeHigh();
led.writeLow();
cli(); // disable interrupts
attachInterrupt(InterruptNumber,onewireInterrupt,FALLING);
// set timer0 interrupt at 250KHz (actually depends on compare match register OCR0A)
// 4us between each tick
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0; // initialize counter value to 0
//TCCR1B |= (1 << WGM12); // turn on CTC mode
//TCCR1B |= (1 << CS11) | (1 << CS10); // Set 64 prescaler
TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
sei(); // enable interrupts
Serial.begin(9600);
}
//int count = 0;
void loop()
{
//if ((count++) % 1000 == 0)
// led.write(!led.read());
cli();//disable interrupts
SerialChannel::swap();
sei();//enable interrupts
SerialChannel::flush();
owHandleReset();
}
void(*timerEvent)() = 0;
void setTimerEvent(short microSecondsDelay, void(*event)())
{
microSecondsDelay -= 10; // this seems to be the typical time taken to initialize the timer on Arduino Uno
short skipTicks = (microSecondsDelay - 3) / 4; // round the micro seconds delay to a number of ticks to skip (4us per tick, so 4us must skip 0 tick, 8us must skip 1 tick, etc.)
if (skipTicks < 1) skipTicks = 1;
//debug.SC_APPEND_STR_INT("setTimerEvent", (long)skipTicks);
TCNT1 = 0;
OCR1A = skipTicks;
timerEvent = event;
TCCR1B = (1 << WGM12) | (1 << CS11) | (1 << CS10); // turn on CTC mode with 64 prescaler
}
void owError(const char* message)
{
debug.append(message);
led.writeHigh();
status = OS_WaitReset;
}
void owClearError()
{
led.writeLow();
}
void owHandleReset()
{
unsigned long localResetStart = resetStart;
if (owPin.read())
{
resetStart = (unsigned long)-1;
}
else if (localResetStart != (unsigned long)-1)
{
unsigned long resetDuration = micros() - localResetStart;
if (resetDuration >= ResetMinDuration)
{
// wait for master to release the pin (or timeout if the pin is pulled low for too long)
unsigned long now = micros();
while (!owPin.read())
{
if (resetStart != localResetStart)
return;
now = micros();
if (now - localResetStart > ResetMaxDuration)
{
owError("Reset too long");
return;
}
}
cli();
owClearError();
lastReset = now;
status = OS_Presence;
setTimerEvent(PresenceWaitDuration - (micros() - now), &beginPresence);
sei();
}
}
}
void onewireInterrupt()
{
//owOutTestPin.writeLow();
onewireInterruptImpl();
//owOutTestPin.writeHigh();
}
//bool debugState = false;
volatile unsigned long lastInterrupt = 0;
void onewireInterruptImpl(void)
{
unsigned long now = micros();
if (now < lastInterrupt + 20)
return; // don't react to our own actions
lastInterrupt = now;
//debugState = !debugState;
//owOutTestPin.write(debugState);
//led.write(state);
resetStart = now;
switch (status) {
case OS_WaitCommand:
{
bool bit = readBit();
/*if (bit)
debug.SC_APPEND_STR("received bit 1");
else
debug.SC_APPEND_STR("received bit 0");*/
receivingByte |= ((bit ? 1 : 0) << receivingBitPos);
++receivingBitPos;
if (receivingBitPos == 8)
{
byte receivedByte = receivingByte;
receivingBitPos = 0;
receivingByte = 0;
//debug.SC_APPEND_STR_INT("received byte", (long)receivedByte);
if (status == OS_WaitCommand && receivedByte == 0xF0)
{
status = OS_SearchRom;
searchROMReadingMasterResponseBit = false;
searchROMSendingInverse = false;
searchROMCurrentByte = 0;
searchROMCurrentBit = 0;
byte currentByte = owROM[searchROMCurrentByte];
searchRomNextBit = bitRead(currentByte, searchROMCurrentBit);
searchRomNextBitToSend = searchROMSendingInverse ? !searchRomNextBit : searchRomNextBit;
attachInterrupt(InterruptNumber, onewireInterruptSearchROM, FALLING);
return;
}
}
} break;
}
}
bool ignoreNextFallingEdge = false;
void onewireInterruptSearchROM()
{
if (ignoreNextFallingEdge)
{
ignoreNextFallingEdge = false;
return;
}
if (searchROMReadingMasterResponseBit)
{
bool bit = readBit();
if (bit != searchRomNextBit)
{
debug.SC_APPEND_STR("Master didn't send our bit, leaving ROM search");
status = OS_WaitReset;
attachInterrupt(InterruptNumber, onewireInterrupt, FALLING);
return;
}
searchROMReadingMasterResponseBit = false;
++searchROMCurrentBit;
if (searchROMCurrentBit == 8)
{
++searchROMCurrentByte;
searchROMCurrentBit = 0;
debug.SC_APPEND_STR("sent another ROM byte");
}
if (searchROMCurrentByte == 8)
{
searchROMCurrentByte = 0;
status = OS_WaitReset;
debug.SC_APPEND_STR("ROM sent entirely");
attachInterrupt(InterruptNumber, onewireInterrupt, FALLING);
return;
}
}
else
{
sendBit(searchRomNextBitToSend);
/*if (bitToSend)
debug.SC_APPEND_STR("sent ROM search bit : 1");
else
debug.SC_APPEND_STR("sent ROM search bit : 0");*/
if (searchROMSendingInverse)
{
searchROMSendingInverse = false;
searchROMReadingMasterResponseBit = true;
}
else
{
searchROMSendingInverse = true;
}
}
byte currentByte = owROM[searchROMCurrentByte];
searchRomNextBit = bitRead(currentByte, searchROMCurrentBit);
searchRomNextBitToSend = searchROMSendingInverse ? !searchRomNextBit : searchRomNextBit;
}
bool readBit()
{
delayMicroseconds(ReadBitSamplingTime);
return owPin.read();
}
void sendBit(bool bit)
{
if (bit)
{
delayMicroseconds(SendBitDuration);
}
else
{
owPullLow();
delayMicroseconds(SendBitDuration);
owRelease();
ignoreNextFallingEdge = true;
}
}
void beginPresence()
{
unsigned long now = micros();
owPullLow();
setTimerEvent(PresenceDuration, &endPresence);
debug.SC_APPEND_STR_TIME("reset", lastReset);
debug.SC_APPEND_STR_TIME("beginPresence", now);
}
void endPresence()
{
unsigned long now = micros();
owRelease();
debug.SC_APPEND_STR_TIME("endPresence", now);
status = OS_WaitCommand;
receivingByte = 0;
receivingBitPos = 0;
bitStart = (unsigned long)-1;
}
ISR(TIMER1_COMPA_vect) // timer1 interrupt
{
TCCR1B = 0; // disable clock
void(*event)() = timerEvent;
timerEvent = 0;
if (event != 0)
event();
}
uint8_t crc8(char addr[], uint8_t len) {
uint8_t crc = 0;
while (len--) {
uint8_t inbyte = *addr++;
for (uint8_t i = 8; i; i--) {
uint8_t mix = (crc ^ inbyte) & 0x01;
crc >>= 1;
if (mix) crc ^= 0x8C;
inbyte >>= 1;
}
}
return crc;
}