 Arduino interrupts Version 5/11-2014

Transcription


Arduino interrupts
Version
5/11-2014
Arduino Timer interrupts.
Hvordan får man Arduino til fx at udføre et interrupt og køre en programstump fx 100 gange i
sekundet.
Interrupts kan udløses på flere forskellige måder. Fx via et signal på en Input-pin, - eller udløst af en
af de indbyggede timere.
Interrupts er programstumper, der udløses af en hændelse og kører asynkront, ikke i et loop. De
udløses fx af et key-tryk, - eller af en tid gået, - timer-overflow, osv.
Interrupts udløses – og udføres et vilkårligt sted i et kørende program – og uafhængig heraf.
Fx kan et program køre – og samtidig kan der af en timer udløses et interrupt, der blinker en LED.
Typisk er der gjort brug af interrupts allerede i de tidligere opgaver, der er lavet.
Det er fordi, Arduino´s underlæggende compiler automatisk indbygger mulighed for at bruge
funktioner som, millis() , micros() og delayMicroseconds(). Disse funktioner gør brug af interrupts
ved brug af timere.
PWM-funktionen analogWrite() bruger timere, ligesom tone(), noTone() og Servo library gør.
Hvad er et interrupt?
Det program, der kører på en controller, er normalt en række af sekventielle udførte instruktioner
efter hinanden.
Et interrupt er en event, udløst enten internt fra en timer / counter, - eller eksternt fra en pin.
Det program, der køres ved eventen, kaldes en interrupt service routine (ISR).
Når en ISR er færdig, vil det kørende program fortsætte hvorfra det blev afbrudt.
Før man kan benytte interrupts, skal der noget opsætning til. Det skal fortælle hvordan og fra hvad,
der skal udløses interrupts.
Interrupts skal enables og den tilhørende interrupt-maske skal enables.
/ Valle Thorø
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Arduino interrupts
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Når der udløses et interrupt, afbryder det igangværende program øjeblikkeligt hvad det er i gang
med, og hopper til en separat programstump kaldet en
Interrupt Service Routine (ISR)
Interrupts can generally enabled / disabled with the function interrupts() / noInterrupts(). By default
in the Arduino firmware interrupts are enabled. Interrupt masks are enabled / disabled by setting /
clearing bits in the Interrupt mask register (TIMSKx).
When an interrupt occurs, a flag in the interrupt flag register (TIFRx) is been set. This interrupt will
be automatically cleared when entering the ISR or by manually clearing the bit in the interrupt flag
register.
Der findes to generelt forskellige interrupts: Pinudløste, - og timer/counter udløste interrupts.
Pin-udløste interrupts.
Pinudløste interrupts kan sættes op til at ske ved en ændring på Arduino-pin 2 eller 3.
Hhv. INT0 & INT1.
Der kan vælges rising eller falling edge. Eller pinchange
Se: http://www.engblaze.com/we-interrupt-this-program-to-bring-you-a-tutorial-on-arduino-interrupts/
Arduino-funktionerne attachInterrupt() og detachInterrupt() bruges kun til pin-udløste interrupts.
Kodeeksempler:
void setup(void)
{
pinMode(2, INPUT);
pinMode(13, OUTPUT);
digitalWrite(2, HIGH);
sei();
EIMSK |= (1 << INT0);
EICRA |= (1 << ISC01);
}
//
//
//
//
Enable pullup resistor
Enable global interrupts
Enable external interrupt INT0
Trigger INT0 on falling edge
void loop(void)
{
}
/ Valle Thorø
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Arduino interrupts
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ISR(EXT_INT0_vect)
Version
5/11-2014
//
// Interrupt Service Routine attached to INT0 vector
{
digitalWrite(13, !digitalRead(13));
// Toggle LED on pin 13
}
http://www.engblaze.com/we-interrupt-this-program-to-bring-you-a-tutorial-on-arduino-interrupts/
Et andet eksempel:
void setup()
{
// Pin 13 is output to which an LED is connected
digitalWrite(13, LOW);
// Make pin 13 low, switch LED off
pinMode(2, INPUT);
// Pin 2 is input to which a switch is connected = INT0
pinMode(3, INPUT);
// Pin 3 is input to which a switch is connected = INT1
attachInterrupt(0, blink1, RISING);
attachInterrupt(1, blink2, RISING);
// attachInterrupt(0, INT0_handler, CHANGE); //
}
void loop() {
/* Nothing to do: the program jumps automatically to Interrupt Service Routine
"blink" in case of a hardware interrupt on Ardiono pin 2 = INT0 */
}
void blink1(){
// Interrupt service routine
digitalWrite(13, HIGH);
}
void blink2(){
digitalWrite(13, LOW);
}
// Interrupt service routine
http://www.geertlangereis.nl/Electronics/Pin_Change_Interrupts/PinChange_en.html
Men det er muligt, at få flere pins til at udføre interrupts. Se
http://www.geertlangereis.nl/Electronics/Pin_Change_Interrupts/PinChange_en.html
Arduino Interrupts
int pbIn = 0;
/ Valle Thorø
// Interrupt 0 is on DIGITAL PIN 2!
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Arduino interrupts
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int ledOut = 4;
volatile int state = LOW;
Version
5/11-2014
// The output LED pin
// The input state toggle
void setup()
{
// Set up the digital pin 2 to an Interrupt and Pin 4 to an Output
pinMode(ledOut, OUTPUT);
//Attach the interrupt to the input pin and monitor for ANY Change
attachInterrupt(pbIn, stateChange, CHANGE);
}
void loop()
{
//Simulate a long running process or complex task
for (int i = 0; i < 100; i++)
{
// do nothing but waste some time
delay(10);
}
}
void stateChange()
{
state = !state;
digitalWrite(ledOut, state);
}
http://www.dave-auld.net/index.php?option=com_content&view=article&id=107:arduino-interrupts&catid=53:arduino-input-outputbasics&Itemid=107
/ Valle Thorø
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Arduino interrupts
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Timerudløste interrupts
Vha. timere kan man opnå, at man kan få et interrupt til at ske med jævne mellemrum. Fx hvis man
ønsker at få opdateret et stopur hver 100-del af et sekund, eller man ønsker at anvende en uC som
frekvensgenerator. Eller fx som cykelcomputer, hvor der skal tælles pulser i en bestemt tid.
Små perioder kan direkte udløses af en timer, - men længere varigheder skal udløses vha. at oprette
en variabel, tæller et antal interrupts. Fx incrementes en tæller 1 gang pr sekund, og når den fx når
60, kan man fx læse en sensor.
En timer/counter kan arbejde på to forskellige måder, når en tid skal udmåles.
Man kan indstille en startværdi for counteren, og så få et interrupt ved overflow, eller man kan tælle
fra 0, og så få et interrupt, når tælleren når en bestemt værdi, indstillet i et register, et Compareregister.
Timer Overflow
Timer Compare Match
Timerens startværdi indstilles, og når timeren
giver overflow, kan der udløses et interrupt.
Der indsættes en værdi i et Compare-register.
Timerens værdi sammenlignes med Compareregisteret, og ved match resettes timeren, og der
kan udløses et interrupt.
Indbyggede timere
Arduino Uno har 3 timere indbygget, timer0, timer1 og timer2.
Timer 0: 8 bit
Timer 1: 16 bit.
Timer 2: 8 bit
AT Mega 2560 har yderligere timer 3, 4 og 5, som er 16 bit
Timerne kan indstilles til at tælle eksterne pulser, eller der kan tælles på krystallets frekvens..
Prescaler. / Frekvensdeler.
På Arduinoen sidder der et 16 MHz krystal. Derfor vil timeren / counteren køre ret hurtigt, og give
fx overflow for en 16 bit register i løbet af ca. 4 mS.
Men heldigvis er der indbygget mulighed for at vælge at neddele clockfrekvensen gennem en
frekvensdeler, eller som det kaldes en prescaler.
/ Valle Thorø
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Prescaleren styres af nogle
bit i to SFR-registre,
TimerCounterControlRegister, TCCRnA eller B
Bittene hedder:
CSn0, CSn1 og CSn2, hvor
tallet n er timerens nummer.
CS står for Clock Select bit.
http://courses.cs.washington.edu/courses/csep567/10wi/lectures/Lecture7.pdf
Der er 2 8-bit setupregistre.
TCCRxA og TCCRxB hvor x er
timer-nummeret.
TCCR står for
Timer/Counter Control Register
Se fx http://forum.arduino.cc/index.php/topic,27390.0.html
CS12
CS11
CS10
Mode Description
0
0
0
Stop Timer/Counter 1
0
0
1
No Prescaler (Timer Clock = System Clock)
0
1
0
divide clock by 8
0
1
1
divide clock by 64
1
0
0
divide clock by 256
1
0
1
divide clock by 1024
1
1
0
increment timer 1 on T1 Pin falling edge
1
1
1
increment timer 1 on T1 Pin rising edge
Prescaler- styre-bit er vist her
for timer 1:
http://www.avrbeginners.net/architecture/timers/timers.html
/ Valle Thorø
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Hjælp til valg af prescaler til forskellige
interruptfrekvenser, se fx calculator på:
http://www.et06.dk/atmega_timers/
Default er disse bit sat til 0.
Prescaler kan vælges til 1, 8, 64, 256, 1024.
( 1024 kan ikke laves på timer 2 )
Udregning af Prescaler-værdi:
For at få affyret et interrupt med en korrekt frekvens, skal man udregne hvor meget man skal dele
krystallets frekvens ned, så timeren ikke når at give overflow. Herefter kan en timers startværdi
udregnes, eller en Compare-Match-værdi.
Der kan findes hjælp på en række hjemmesider til at vælge den rette precaler til et bestemt formål.
Se fx:
http://www.et06.dk/atmega_timers/
Skal forbedres!
Udregningen sker som flg:
(timer speed (Hz)) = (Arduino clock speed (16MHz)) / prescaler
𝑖𝑛𝑡𝑒𝑟𝑟𝑢𝑝𝑡 𝑓𝑟𝑒𝑘𝑣𝑒𝑛𝑠 =
16 𝑀𝐻𝑧
𝑃𝑟𝑒𝑠𝑐𝑎𝑙𝑒𝑟 ∙ ((𝐶. 𝑀𝑎𝑡𝑐ℎ 𝑟𝑒𝑔) + 1)
( + 1 fordi det tager 1 clock cycle at resette.
/ Valle Thorø
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Ligningen løst for Compare match register, CMR:
16.000.000
𝐶𝑀𝑅 = (
)−1
𝑃𝑟𝑒𝑠𝑐𝑎𝑙𝑒𝑟 ∙ 𝑖𝑛𝑡𝑒𝑟𝑟𝑢𝑝𝑡 𝑓𝑟𝑒𝑘𝑣.
Værdien skal være mindre end 256 for timer 0 og 2, og mindre end 65.536 for Timer 1 for at det
kan lade sig gøre:
Eksempel:
Clock select and timer frequency
Different clock sources can be selected for each timer independently. To calculate the timer frequency (for
example 2Hz using timer1) you will need:
1.
2.
3.
4.
CPU frequency 16Mhz for Arduino
maximum timer counter value (256 for 8bit, 65536 for 16bit timer)
Divide CPU frequency through the choosen prescaler (16000000 / 256 = 62500)
Divide result through the desired frequency (62500 / 2Hz = 31250)
Verify the result against the maximum timer counter value (31250 < 65536 success) if fail, choose
bigger prescaler.
5.
Eksempel på opsætning til 1 HZ interrupt:
Interrupt every second (frequency of 1Hz):
compare match register = [16,000,000 / (prescaler * 1) ] -1
with a prescaler of 1024 you get:
compare match register = [16,000,000 / (1024 * 1) ] -1 = 15,624
since 256 < 15,624 < 65,536, you must use timer1 for this interrupt.
Timer setup code is done inside the setup(){} function in an Arduino sketch.
Control registrere til timerne mm.
For at man kan styre timerne er der en del kontrol-registre, hvis bit – eller indhold skal bestemmes.
Hver timer har et antal registre tilknyttet.

TCCRx - Timer/Counter Control Register. The pre-scaler can be configured here.

TCNTx - Timer/Counter Register. The actual timer value is stored here.

OCRx - Output Compare Register
/ Valle Thorø
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
TIMSKx - Timer/Counter Interrupt Mask Register. To enable/disable timer
interrupts.

TIFRx - Timer/Counter Interrupt Flag Register. Indicates a pending timer
interrupt.
Følgende diagram er et forsøg på at lave et samlet diagram over en timer og interrupt-struktur
Arduino Timer1 Interrupt-Opsætning
ATMEL AVR
ATMEGA328
CTC Mode Interrupt ( Clear Timer on Compare Match )
Enable Interrupt i reg:
Enable / Disable Global Interrupt
Timer Interrupt Mask register
interrupts ();
noInterrupts ();
TIMSK1-Bit: [xxxx x, OCIE1B, OCIE1A, TOIE1]
Sei(); Cli();Disable
Compare_Match: TIMSK1 = B00000010;
Brug kun i Setup() ??
TIMSK1
TIMSK1 |= ( 1 << OCIE1A );
Overflow bit, Bit 0
bitSet(TCCR1B, OCIE1A); Bit OCIE1A
Bit OCIE1A
TIMSK1 = B00000010;
TIMSK1 = B00000001;
2
bitSet(TCCR1B, TOIE1);
2
1
( Der er også en kanal B & C )
Vector
1
3
( Kun Kanal A Clearer timeren )
3
Eks: OCR1A = 15624;
OCRnC
Timer/Counter Interrupt
ISR(Timer1_COMPA_Vect)
Flag Register
{
Output Compare Register
OCRnB
}
Output Compare Interrupt
OCR1A
TIFR1
Flag OCF1A og Overflov
flag TOV1 cleares af
Timer Compare Value
ISR(TIMER1_OVF_vect)
hardware ved interrupt kald
2
16 Bit
{
Sæt OCF1A
1 bit
}
16 Bit
3
16 Bit
Compare
Sæt TOV1 Bit
Timer Overflow Bit Flag
TCNT1H
TCNT1L
Timer/Counter 1H
Timer/Counter 1L
TCNT1 = 0;
TCNT1 = 25324;
Oscillator
16 MHz
Frekvensdeler
= Prescaler
Reset Counter
Clock-pulser, f = ( osc / prescale )
Timer0 bruges til delay(); millis(); & micros();
Timer1 til servo();
Timer2 til tone();
Timer 0 & 2
er kun 8 bit
[ CSxx = Clock Select bit ]
TCCR1B-Bit[xxxx WGM12, CS12, CS11, CS10 ]
TCCR1B |= B*****xxx;
TCCR1B |= ( 1 << CS12 ) | ( 1 << CS10 );// = 1024
TCCR1B |= 0x05;
// = 1024
bitSet(TCCR1B, CS10);
bitSet(TCCR1B, CS12);
Pins ( Bit 7 - 0 )
DDRB
Data Direction Reg.
DDRB |= B00001111;
( 1 = output )
PORTB
Port Reg
PORTB = B00001111;
Fra Pins
TCCR1A
TCCR1B
Timer/Counter Control Register A/B
Mode select registre
[CS12, CS11, CS10]
000 Stop Timer
001 Divide by 1
010
8
011
64
100
256
101
1024
11* Ekstern clock på T1
CS10 = 0
CS11 = 1
CS12 = 2
TCCR1B |= ( 1 << WGM12 ); Turn on Compare ( CTC ) Mode( Wave Generation Mode )
TCCR1B |= B00001000;
bitSet(TCCR1B, WGM12);
Default er Counter Overflow Mode Valgt ( Normal mode )
/ Valle Sept 2013
Rev: 02/04-2014
Tegningen viser de forskellige registre involveret i opsætningen, og der er givet forskellige
eksempler på hvordan man kan manipulere med bittene i registrene:
Her er en kort oversigt over, hvad der skal opsættes:
Hvad skal gøres? Kode-eksempel
Disable global interrupt cli();
Nulstil tæller TCNT1 = 0;
Compare værdien skal indstilles OCR1A = 15624;
* Vælg CTC Mode TCCR1B |= (1 << WGM12); **
Prescaler-værdien skal indstilles TCCR1B |= (1 << CS10);
TCCR1B |= (1 << CS12);
/ Valle Thorø
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Timer interrupt skal enables TIMSK1 |= (1 << OCIE1A);
Enabel Global Timer interrupt sei();
*
Timerne kan arbejde i et større antal modes, derfor skal man vælge: CTC Mode ( Counter-TimerCompare ?? )
**
Notice how the setups between the three timers differ slightly in the line which turns on CTC mode:
TCCR0A |= (1 << WGM01);
TCCR1B |= (1 << WGM12);
TCCR2A |= (1 << WGM21);
//for timer0
//for timer1
//for timer2
This follows directly from the datasheet of the ATMEL 328/168 Kilde # .1
Timer Mode select:
Waveform Generation Bit setup:
Timerne kan tillige indstilles til at
hav af forskellige funktioner. Det
styres af ” Waveform generation
bits” også i reg. TCCR1A og
TCCR1B.
Det eneste bit der har interesse her
er WGM12, som vælger CTC
mode.
Interrupt subrutiner
Her er vist, hvordan man skriver en interrupt-subrutine, en Interrupt Service Rutine.
Eks:
ISR(TIMER1_COMPA_vect)
{
seconds++;
1
// Compare match
Fra: (http://www.instructables.com/id/Arduino-Timer-Interrupts/step2/Structuring-Timer-Interrupts/ )
Datablad:
/ Valle Thorø
http://www.atmel.com/Images/doc8161.pdf
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if (seconds == 10)
{
seconds = 0;
readMySensor();
}
}
{
TCNT1 = timer1_counter;
// Overflow interrupt service routine
// preload timer med værdi, fx med 23445
digitalWrite(ledPin, digitalRead(ledPin) ^ 1);
}
void loop()
{
// your program here...
}
Timer Overflow eksempler:
Timer overflow means the timer has reached is limit value. When a timer overflow interrupt occurs,
the timer overflow bit TOVx will be set in the interrupt flag register TIFRx. When the timer
overflow interrupt enable bit TOIEx in the interrupt mask register TIMSKx is set, the timer
overflow interrupt service routine ISR(TIMERx_OVF_vect) will be called.
I denne mode presettes timerne til en startværdi, - og overflow udløser så et interrupt.
Der kan også tilsluttes en ekstern klock-frekvens. Dvs. man kan tælle eksterne pulser.
Men de fleste gange bliver den interne oscillator-frekvens brugt.
/*
* Arduino 101: timer and interrupts
* Timer1 overflow interrupt example
* more infos: http://www.letmakerobots.com/node/28278
* created by RobotFreak
*/
#define ledPin 13
void setup()
/ Valle Thorø
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{
pinMode(ledPin, OUTPUT);
// initialize timer1
noInterrupts();
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 34286;
TCCR1B |= (1 << CS12);
TIMSK1 |= (1 << TOIE1);
interrupts();
// disable all interrupts
//
//
//
//
preload timer 65536-16MHz/256/2Hz
256 prescaler
enable timer overflow interrupt
enable all interrupts
}
// interrupt service routine that wraps a user defined
function supplied by attachInterrupt
{
TCNT1 = 34286;
// preload timer
}
void loop()
{
}
// Se: http://www.hobbytronics.co.uk/arduino-timer-interrupts
#define ledPin 13
int timer1_counter;
void setup()
{
noInterrupts();
TCCR1A = 0;
TCCR1B = 0;
// Set timer1_counter to the correct value for our interrupt interval
//timer1_counter = 64886;
// preload timer 65536-16MHz/256/100Hz
//timer1_counter = 64286;
timer1_counter = 34286;
TCCR1B |= (1 << CS12);
TIMSK1 |= (1 << TOIE1);
/ Valle Thorø
// preload timer
// 256 prescaler
( |= betyder Bitwise or. )
// enable timer overflow interrupt
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interrupts();
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// enable all interrupts
}
// interrupt service routine
{
// preload timer
}
void loop()
{
}
Output Compare Match eksempler:
When a output compare match interrupt occurs, the OCFxy flag will be set in the interrupt flag
register TIFRx . When the output compare interrupt enable bit OCIExy in the interrupt mask
register TIMSKx is set, the output compare match interrupt service ISR(TIMERx_COMPy_vect)
routine will be called.
Timerne kan udløse et interrupt hver gang, en timer når op til samme værdi, som er gemt i et timermatch register, - eller hvis de når deres max count-værdi, og giver overflow.
Når en timer når et match,- bliver det resat på det næste klockpuls – og fortsætter så opad igen fra 0
til næste match.
Ved at vælge Compare match værdien, - og vælge klock-frekvensen ( 16 MHz ) sammen med en
frekvensdeler, en prescaler, kan man kontrollere interruptfrekvensen.
Timeren sætter ved overflow en overflow bit som evt. kan tjekkes manuelt af programmet.
ISR-en ( Interrupt Service Routine resetter overflowbit.
/* Arduino 101: timer and interrupts
Timer1 compare match interrupt example
more infos: http://www.letmakerobots.com/node/28278
created by RobotFreak
*/
#define ledPin 13
void setup()
{
/ Valle Thorø
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noInterrupts();
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
OCR1A = 31250;
TCCR1B |= (1 << WGM12);
TCCR1B |= (1 << CS12);
TIMSK1 |= (1 << OCIE1A);
interrupts();
//
//
//
//
//
compare match register 16MHz/256/2Hz
CTC mode
256 prescaler
enable timer compare interrupt
enable all interrupts
}
// timer compare interrupt service routine
{
// toggle LED pin
}
void loop()
{
}
// Arduino timer CTC interrupt example
#define LEDPIN 2
void setup()
{
pinMode(LEDPIN, OUTPUT);
cli();
TCCR1A = 0;
TCCR1B = 0;
OCR1A = 15624;
TCCR1B |= (1 <<
TCCR1B |= (1 <<
TCCR1B |= (1 <<
TIMSK1 |= (1 <<
sei();
// initialize Timer1
// disable global interrupts
// set entire TCCR1A register to 0
// same for TCCR1B
// set compare match register to desired timer count:
WGM12);
// turn on CTC mode:
CS10);
// Set CS10 and CS12 bits for 1024 prescaler:
CS12);
OCIE1A);
// enable timer compare interrupt:
// enable global interrupts:
}
void loop()
/ Valle Thorø
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{
// do some crazy stuff while my LED keeps blinking
}
{
digitalWrite(LEDPIN, !digitalRead(LEDPIN));
}
Eksempel på, at tælle antal interrupts, for at få noget til at foregå langsommere!
{
seconds++;
if (seconds == 10)
{
seconds = 0;
readMySensor();
}
}
void setup()
{
//Use timer 5, output A
noInterrupts();
TCCR5A = 0;
TCCR5B = 0;
TCNT5 = 0;
(pin 44)
OCR5A = 833;
// compare match register 16MHz/256/75Hz ~75.03Hz
TCCR5B |= (1 << WGM12);
// CTC mode
TCCR5B |= (1 << CS12);
// 256 prescaler
TIMSK5 |= (1 << OCIE5A); // enable timer compare interrupt mask
interrupts();
// enable all interrupts
}
void loop()
{
}
// timer compare ISR
{
Serial.print(" et eller andet");
//print RTI fire time
/ Valle Thorø
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}
//
//
Denne interrupt kaldes ved 1kHz
http://petemills.blogspot.dk/2011/05/real-time-clock-part-1.html
{
static uint16_t milliseconds = 0; // mS value for timekeeping 1000mS/1S
static uint16_t clock_cal_counter = 0; // counting up the milliseconds to MS_ADJ
const uint16_t MS_ADJ = 35088;
// F_CPU / (F_CPU * PPM_ERROR)
const uint16_t MS_IN_SEC = 1000; // 1000mS/1S
milliseconds++;
clock_cal_counter++;
if( milliseconds >= MS_IN_SEC )
{
milliseconds = 0;
ss++;
// increment seconds
toggle_led();
// toggle led
if( ss > 59 )
{
mm++;
// increment minutes
ss = 0;
// reset seconds
}
if( mm > 59 )
{
hh++;
// increment hours
mm = 0;
// reset minutes
}
if( hh > 23 )
{
// increment day
hh = 0;
// reset hours
}
}
//
//
//
//
milliseconds must be less than 999 to avoid missing an adjustment.
eg if milliseconds were to be 999 and we increment it here to 1000
the next ISR call will make it 1001 and reset to zero just as if it
would for 1000 and the adjustment would be effectively canceled out.
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if( ( clock_cal_counter >= MS_ADJ ) && ( milliseconds < MS_IN_SEC - 1 ) )
{
milliseconds++;
// it may be that clock_cal_counter is > than MS_ADJ in which case
// I want to count the tick towards the next adjustment
// should always be 1 or 0
clock_cal_counter = clock_cal_counter - MS_ADJ;
}
}
What are "volatile" variables?
Variables shared between ISR functions and normal functions should be declared "volatile". This
tells the compiler that such variables might change at any time, and thus the compiler must reload
the variable whenever you reference it, rather than relying upon a copy it might have in a processor
register.
For example:
volatile boolean flag;
// Interrupt Service Routine (ISR)
void isr ()
{
flag = true;
} // end of isr
void setup ()
{
attachInterrupt (0, isr, CHANGE);
} // end of setup
// attach interrupt handler
void loop ()
{
if (flag)
{
// interrupt has occurred
}
} // end of loop
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Flere noter:
(Note that there are two other OCR (OCR1B and OCR1C not used in this example. However they
may be used independent of OCR1A to generate another frequency or other Timer Counter
Functions.
When that value is reached the output toggles provided that the corresponding output pin is set to
output mode. )
Der er flere måder, hvorpå man kan få udløst et interrupt på tid:
Kode til at sætte værdier i kontrolregistre:
I flere Kode-eksempler er der vist en metode til at indstille registre-bits til interrupt-styring ved at
skifte en kode til venstre.
Fx:
TCCR1B |= (1 << CS12);
// 256 prescaler , skift et ‘1’-tal så mange pladser til
venstre, som værdien af CS12.
|= betyder Bitwise or.)
Det kan fx bruges, hvis man ikke kender placeringen af bittene i timer kontrol-registrene. Men det
kræver til gengæld, at man ved, at bit CSn2 skal sættes.
I eksemplet skiftes et 1-tal til venstre et antal gange, angivet af værdien af CS12. Compileren
kender denne værdi!
Prædefinerede værdier, som compileren kender:
De er defineret i en include-fil:
#define CS00 0
#define CS01 1
#define CS02 2
#define TOIE1 0
Se: http://courses.cs.washington.edu/courses/csep567/10wi/lectures/Lecture7.pdf
Ved man hvilke bit der skal sættes i et register, kan man gøre det med en af følgende muligheder:
TCCR1A = 0b10101010;
TCCR1A = 0;
TCCR1B = 0;
/ Valle Thorø
// sæt hele TCCR1A register til 0
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TCCR1B
TCCR2A
TCCR2B
TCCR2B
= 0x03;
= B01000011;
= B00001001;
|= 7;
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// her kendes hvilke bits, der skal sættes.
//Clock select. Internal, prescale 1024~64us
TCCR0A = _BV(WGM01);
TCCR0B = _BV(CS02) | _BV(CS00);
// Mode = CTC
// _BV er en function, der ???
/* _BV(x) er en funktion, der skifter et 1-tal x pladser til venstre.
Det betyder, at fx _BV(6) returnerer 0b01000000
*/
Bitmanipulation sker med disse instruktioner:
Fra side om C-bitmanipulation:
| bit OR
& bit AND
~ bit NOT
^ bit EXLUSIVE OR (XOR)
<< bit LEFT SHIFT
>> bit RIGHT SHIFT
http://tom-itx.dyndns.org:81/~webpage/avr/c_bits/bits_index.php
Interrupt subrutine:
En interrupt service rutine definers som følgende:
ISR(Timerx_ COMPA_VECT) {
Do something
}
Eksempel:
Arduino timer compare match interrupts:
Eksempler på opsætning af Prescaler:
void setup(){
cli();
//stop interrupts
//set timer0 interrupt at 2kHz
TCCR0A = 0;
TCCR0B = 0;
// same for TCCR0B
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TCNT0 = 0;
OCR0A = 124;
//initialize counter value to 0
// set compare match register for 2khz
// increments
// = (16*10^6) / (2000*64) - 1 (must be <256)
TCCR0A |= (1 << WGM01);
// turn on CTC mode
TCCR0B |= (1 << CS01) | (1 << CS00); // Set CS01 and CS00 bits for 64 presc.
// enable timer compare interrupt
//set timer1 interrupt at 1Hz
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
OCR1A = 15624;
// set entire TCCR1A register
// same for TCCR1B
//initialize counter value to
// set compare match register
// increments
// = (16*10^6) / (1*1024) - 1
to 0
0
for 1hz
(must be <65536)
TCCR1B |= (1 << WGM12);
// turn on CTC mode
TCCR1B |= (1 << CS12) | (1 << CS10); // Set CS10 og CS12 bits for 1024 presc.
//set timer2 interrupt
TCCR2A = 0;
TCCR2B = 0;
TCNT2 = 0;
OCR2A = 249;
at 8kHz
// set entire TCCR2A register
// same for TCCR2B
//initialize counter value to
// set compare match register
// increments
// = (16*10^6) / (8000*8) - 1
TCCR2A |= (1 << WGM21);
TCCR2B |= (1 << CS21);
0
for 8khz
(must be <256)
// turn on CTC mode
// Set CS21 bit for 8 prescaler
sei();
//allow interrupts
}
//end setup
ISR(TIMER0_COMPA_vect){
to 0
//change the 0 to 1 for timer1 and 2 for timer2
//interrupt commands here
}
http://www.instructables.com/id/Arduino-Timer-Interrupts/
Resten er endnu ikke helt gennemarbejdet, kan betragtes som Bonus Info
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TIMSK1. This is the Timer/Counter1 Interrupt Mask Register. Setting the TOIE1 bit tells the timer to
trigger an interrupt when the timer overflows.
TIMSK and TIFR
The Timer Interrupt Mask Register (TIMSK) and Timer Interrupt Flag (TIFR) Register are used to control which interrupts
are "valid" by setting their bits in TIMSK and to determine which interrupts are currently pending (TIFR).
Bit 7
TOIE1 OCIE1A
---
---
TICIE1
---
TOIE0
Bit 0
---
TOIE1: Timer Overflow Interrupt Enable (Timer 1); If this bit is set and if global interrupts are enabled, the micro will jump
to the Timer Overflow 1 interrupt vector upon Timer 1 Overflow.
OCIE1A: Output Compare Interrupt Enable 1 A; If set and if global Interrupts are enabled, the micro will jump to the
Output Compare A Interrupt vetor upon compare match.
TICIE1: Timer 1 Input Capture Interrupt Enable; If set and if global Interrupts are enabled, the micro will jump to the Input
Capture Interrupt vector upon an Input Capture event.
TOIE0: Timer Overflow Interrupt Enable (Timer 0); Same as TOIE1, but for the 8-bit Timer 0.
TCCR1A = 0x00;
// COM1A1=0, COM1A0=0 => Disconnect Pin OC1 from Timer/Counter 1 -PWM11=0,PWM10=0 => PWM Operation disabled, ICNC1=0 => Capture Noise Canceler
disabled -- ICES1=0 => Input Capture Edge Select (not used) -- CTC1=0 => Clear
Timer/Counter 1 on Compare/Match, CS12=0 CS11=1 CS10=1 => Set prescaler to
clock/64
TCCR1B = 0x03;
// 16MHz clock with prescaler means TCNT1 increments every 4uS,
ICIE1=0 => Timer/Counter 1, Input Capture Interrupt Enable -- OCIE1A=0 => Output
Compare A Match Interrupt Enable -- OCIE1B=0 => Output Compare B Match Interrupt
Enable
TOIE1=0 => Timer 1 Overflow Interrupt Enable
TCCR3A register
COM3A1
COM3A0
TCCR3B register
ICNC3
ICES3
/ Valle Thorø
COM3B1
–
COM3B0
COM3C1
COM3C0
WGM11
WGM10
WGM13
WGM12
CS12
CS11
CS10
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based on the AT90S2313.
16 bit timere er
lidt mere
complex.
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Timer overflow og interrupt udløses :
Output Compare Mode
The Output Compare mode is used to
perform repeated timing. The value in
TCNT1 (which is counting up if not
stopped by the prescaler select bits) is
permanently compared to the value in
OCR1A. When these values are equal to
each other, the Output Compare Interrupt
Flag (OCF in TIFR) is set and an ISR can
be called. By setting the CTC1 bit in
TCCR1B, the timer can be automatically
cleared upon compare match.
/ Valle Thorø
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http://www.nunoalves.com/classes/spring_2012_cpe355/cpe355-02-b.pdf
http://www.gammon.com.au/forum/?id=11488
http://www.protostack.com/blog/2010/09/timer-interrupts-on-an-atmega168/
Gode oversigter over register!
Example- the following sketch sets up and executes 3 timer interrupts:
//timer interrupts
//by Amanda Ghassaei
//June 2012
//http://www.instructables.com/id/Arduino-Timer-Interrupts/
/*
*
*
*
*
*
*/
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
//timer setup for timer0, timer1, and timer2.
//For arduino uno or any board with ATMEL 328/168.. diecimila, duemilanove,
lilypad, nano, mini...
//this code will enable
//timer0 will interrupt
all three arduino timer interrupts.
at 2kHz
at 1Hz
at 8kHz
//storage variables
boolean toggle0 = 0;
void setup(){
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
cli();
/ Valle Thorø
//set pins as outputs
//stop interrupts
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TCCR0A = 0;
TCCR0B = 0;
TCNT0 = 0;
OCR0A = 124;
// same for TCCR2B
// increments
// = (16*10^6) / (2000*64) - 1 (must be <256)
TCCR0A |= (1 << WGM01);
// turn on CTC mode
TCCR0B |= (1 << CS01) | (1 << CS00);
// Set CS01 and CS00 bits for 64
// prescaler
//set timer1 interrupt at 1Hz
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
// same for TCCR1B
// set compare match register for 1hz
// increments
OCR1A = 15624;
// = (16*10^6) / (1*1024) - 1 (must be <65536)
TCCR1B |= (1 << WGM12);
// turn on CTC mode
TCCR1B |= (1 << CS12) | (1 << CS10);
// Set CS12 and CS10 bits for 1024
//prescaler
TCCR2A = 0;
TCCR2B = 0;
TCNT2 = 0;
OCR2A = 249;
TCCR2A |= (1 << WGM21);
TCCR2B |= (1 << CS21);
// same for TCCR2B
// increments
// = (16*10^6) / (8000*8) - 1 (must be <256)
// turn on CTC mode
sei();//allow interrupts
}//end setup
//timer0 interrupt 2kHz toggles pin 8
//generates pulse wave of frequency 2kHz/2 =
//1kHz (takes two cycles for full wave- toggle
// high then toggle low)
if (toggle0){
digitalWrite(8,HIGH);
toggle0 = 0;
}
else{
digitalWrite(8,LOW);
toggle0 = 1;
}
}
/ Valle Thorø
//timer1 interrupt 1Hz toggles pin 13 (LED)
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//generates pulse wave of frequency 1Hz/2 =
//0.5kHz (takes two cycles for full wave//toggle high then toggle low)
if (toggle1){
toggle1 = 0;
}
else{
toggle1 = 1;
}
}
//timer1 interrupt 8kHz toggles pin 9
//generates pulse wave of frequency 8kHz/2 =
//4kHz (takes two cycles for full wave- toggle
// high then toggle low)
if (toggle2){
toggle2 = 0;
}
else{
toggle2 = 1;
}
}
void loop(){
//do other things here
}
The images above show the outputs from these timer interrupts. Fig 1 shows a square wave oscillating
between 0 and 5V at 1kHz (timer0 interrupt), fig 2 shows the LED attached to pin 13 turning on for one
second then turning off for one second (timer1 interrupt), fig 3 shows a pulse wave oscillating between
0 and 5V at a frequency of 4khz (timer2 interrupt).
Bike Speedometer
In this example I made an arduino bike speedometer. It works by attaching a magnet to the wheel and
measuring the amount of time it takes to pass by a magnetic switch mounted on the frame- the time for
one complete rotation of the wheel.
I set timer 1 to interrupt every ms (frequency of 1kHz) to measure the magnetic switch. If the magnet is
passing by the switch, the signal from the switch is high and the variable "time" gets set to zero. If the
magnet is not near the switch "time" gets incremented by 1. This way "time" is actually just a
measurement of the amount of time in milliseconds that has passed since the magnet last passed by
the magnetic switch. This info is used later in the code to calculate rpm and mph of the bike.
Here's the bit of code that sets up timer1 for 1kHz interrupts
Here's the complete code if you want to take a look:
//bike speedometer
//by Amanda Ghassaei 2012
/ Valle Thorø
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/*
*
*
*
*
*
*/
//sample calculations
//tire radius ~ 13.5 inches
//circumference = pi*2*r =~85 inches
//max speed of 35mph =~ 616inches/second
//max rps =~7.25
#define reed A0//pin connected to read switch
//storage variables
float radius = 13.5;// tire radius (in inches)- CHANGE THIS FOR YOUR OWN BIKE
int reedVal;
long time = 0;// time between one full rotation (in ms)
float mph = 0.00;
float circumference;
boolean backlight;
int maxReedCounter = 100;//min time (in ms) of one rotation (for debouncing)
int reedCounter;
void setup(){
reedCounter = maxReedCounter;
circumference = 2*3.14*radius;
pinMode(1,OUTPUT);//tx
pinMode(2,OUTPUT);//backlight switch
pinMode(reed,INPUT);//redd switch
checkBacklight();
Serial.write(12);//clear
// TIMER SETUP- the timer interrupt allows preceise timed measurements of the reed
switch
//for mor info about configuration of arduino timers see
http://arduino.cc/playground/Code/Timer1
cli();//stop interrupts
TCCR1A = 0;// set entire TCCR1A register to 0
TCCR1B = 0;// same for TCCR1B
TCNT1 = 0;//initialize counter value to 0;
// set timer count for 1khz increments
OCR1A = 1999;// = (16*10^6) / (1000*8) - 1
// turn on CTC mode
TCCR1B |= (1 << WGM12);
TCCR1B |= (1 << CS11);
//END TIMER SETUP
/ Valle Thorø
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Serial.begin(9600);
}
void checkBacklight(){
backlight = digitalRead(2);
if (backlight){
Serial.write(17);//turn backlight on
}
else{
Serial.write(18);//turn backlight off
}
}
ISR(TIMER1_COMPA_vect) {//Interrupt at freq of 1kHz to measure reed switch
reedVal = digitalRead(reed);//get val of A0
if (reedVal){//if reed switch is closed
if (reedCounter == 0){//min time between pulses has passed
mph = (56.8*float(circumference))/float(time);//calculate miles per hour
time = 0;//reset timer
reedCounter = maxReedCounter;//reset reedCounter
}
else{
if (reedCounter > 0){//don't let reedCounter go negative
reedCounter -= 1;//decrement reedCounter
}
}
}
else{//if reed switch is open
if (reedCounter > 0){//don't let reedCounter go negative
reedCounter -= 1;//decrement reedCounter
}
}
if (time > 2000){
mph = 0;//if no new pulses from reed switch- tire is still, set mph to 0
}
else{
time += 1;//increment timer
}
}
void displayMPH(){
Serial.write(12);//clear
Serial.write("Speed =");
Serial.write(13);//start a new line
Serial.print(mph);
Serial.write(" MPH ");
//Serial.write("0.00 MPH ");
}
void loop(){
//print mph once a second
displayMPH();
delay(1000);
checkBacklight();
}
For this project, I used timer2 interrupts to periodically check if there was any incoming serial data, read
it, and store it in the matrix "ledData[]". If you take a look at the code you will see that the main loop of
/ Valle Thorø
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the sketch is what is actually responsible for using the info in ledData to light up the correct LEDs and
checking on the status of the buttons (a function called "shift()"). The interrupt routine is as short as
possible- just checking for incoming bytes and storing them appropriately.
Here is the setup for timer2:
//set timer2 interrupt every 128us
TCNT2 = 0;//initialize counter value to 0
// set compare match register for 7.8khz increments
OCR2A = 255;// = (16*10^6) / (7812.5*8) - 1 (must be <256)
// turn on CTC mode
TCCR2A |= (1 << WGM21);
TCCR2B |= (1 << CS21);
Here's the complete Arduino sketch:
//BUTTON TEST w/ 74HC595 and 74HC165 and serial communication
//by Amanda Ghassaei
//June 2012
/*
*
*
*
*
*
*/
//this firmware will send data back and forth with the maxmsp patch "beat slicer"
//pin connections
#define ledLatchPin A1
#define ledClockPin A0
#define ledDataPin A2
#define buttonLatchPin 9
#define buttonClockPin 10
#define buttonDataPin A3
//looping variables
byte i;
byte j;
byte k;
byte ledByte;
//storage for led states, 4 bytes
byte ledData[] = {0, 0, 0, 0};
//storage for buttons, 4 bytes
byte buttonCurrent[] = {0,0,0,0};
byte buttonLast[] = {0,0,0,0};
byte buttonEvent[] = {0,0,0,0};
byte buttonState[] = {0,0,0,0};
//button debounce counter- 16 bytes
byte buttonDebounceCounter[4][4];
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void setup() {
DDRC = 0xF7;//set A0-2 and A4-5 output, A3 input
DDRB = 0xFF;//digital pins 8-13 output
Serial.begin(57600);
//set timer2 interrupt every 128us
TCNT2 = 0;//initialize counter value to 0
// set compare match register for 7.8khz increments
OCR2A = 255;// = (16*10^6) / (7812.5*8) - 1 (must be <256)
// turn on CTC mode
TCCR2A |= (1 << WGM21);
TCCR2B |= (1 << CS21);
}
// buttonCheck - checks the state of a given button.
//this buttoncheck function is largely copied from the monome 40h firmware by brian
crabtree and joe lake
void buttonCheck(byte row, byte index)
{
if (((buttonCurrent[row] ^ buttonLast[row]) & (1 << index)) &&
// if the current
physical button state is different from the
((buttonCurrent[row] ^ buttonState[row]) & (1 << index))) { // last physical button
state AND the current debounced state
if (buttonCurrent[row] & (1 << index)) {
// if the current
physical button state is depressed
buttonEvent[row] = 1 << index;
// queue up a new button event
immediately
buttonState[row] |= (1 << index);
// and set the debounced
state to down.
}
else{
buttonDebounceCounter[row][index] = 12;
} // otherwise the button was previously depressed and now
// has been released so we set our debounce counter.
}
else if (((buttonCurrent[row] ^ buttonLast[row]) & (1 << index)) == 0 && // if the
current physical button state is the same as
(buttonCurrent[row] ^ buttonState[row]) & (1 << index)) {
// the last physical
button state but the current physical
// button state is different from the current debounce
// state...
if (buttonDebounceCounter[row][index] > 0 && --buttonDebounceCounter[row][index] ==
0) { // if the the debounce counter has
// been decremented to 0 (meaning the
// the button has been up for
// kButtonUpDefaultDebounceCount
// iterations///
buttonEvent[row] = 1 << index;
// queue up a button state change event
if (buttonCurrent[row] & (1 << index)){
/ Valle Thorø
// and toggle the buttons
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debounce state.
buttonState[row] |= (1 << index);
}
else{
buttonState[row] &= ~(1 << index);
}
}
}
}
void shift(){
for (i=0;i<4;i++){
buttonLast[i] = buttonCurrent[i];
byte dataToSend = (1 << (i+4)) | (15 & ~ledData[i]);
// set latch pin low so the LEDs don't change while sending in bits
digitalWrite(ledLatchPin, LOW);
// shift out the bits of dataToSend
shiftOut(ledDataPin, ledClockPin, LSBFIRST, dataToSend);
//set latch pin high so the LEDs will receive new data
digitalWrite(ledLatchPin, HIGH);
//once one row has been set high, receive data from buttons
//set latch pin high
digitalWrite(buttonLatchPin, HIGH);
//shift in data
buttonCurrent[i] = shiftIn(buttonDataPin, buttonClockPin, LSBFIRST) >> 3;
//latchpin low
digitalWrite(buttonLatchPin, LOW);
for (k=0;k<4;k++){
buttonCheck(i,k);
if (buttonEvent[i]<<k){
if (buttonState[i]&1<<k){
Serial.write(((3-k)<<3)+(i<<1)+1);
}
else{
Serial.write(((3-k)<<3)+(i<<1)+0);
}
buttonEvent[i] &= ~(1<<k);
}
}
}
}
ISR(TIMER2_COMPA_vect) {
do{
if (Serial.available()){
ledByte = Serial.read();//000xxyys
boolean ledstate = ledByte & 1;
byte ledy = (ledByte >> 1) & 3;
byte ledx = (ledByte >> 3) & 3;
if (ledstate){
ledData[ledy] |= 8 >> ledx;
}
else{
ledData[ledy] &= ~ (8 >> ledx);
}
}//end if serial available
}//end do
/ Valle Thorø
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while (Serial.available() > 8);
}
void loop() {
shift();//updates leds and receives data from buttons
}
One last thing to note- certain timer setups will actually disable some of the Arduino library
functions. Timer0 is used by the functions millis() and delay(), if you manually set up timer0, these
functions will not work correctly.
Additionally, all three timers underwrite the function analogWrite(). Manually setting up a timer will stop
analogWrite() from working.
If there is some portion of your code that you don't want interrupted, considering using cli() and sei() to
globally disable and enable interrupts.
You can read more about this on the Arduino website.
/ Valle Thorø
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Stopwatch http://playground.arduino.cc/Code/Stopwatch
A sketch that demonstrates how to do two (or more) things at once by using millis().
/* StopWatch
* Paul Badger 2008
* Demonstrates using millis(), pullup resistors,
* making two things happen at once, printing fractions
*
* Physical setup: momentary switch connected to pin 4, other side
connected to ground
* LED with series resistor between pin 13 and ground
*/
#define ledPin 13
#define buttonPin 4
// LED connected to digital pin 13
// button on pin 4
int value = LOW;
int buttonState;
int lastButtonState;
state
int blinking;
timing
long interval = 100;
long previousMillis = 0;
was updated
long startTime ;
long elapsedTime ;
int fractional;
part of time
// previous value of the LED
// variable to store button state
// variable to store last button
// condition for blinking - timer is
// blink interval - change to suit
// variable to store last time LED
// start time for stop watch
// elapsed time for stop watch
// variable used to store fractional
void setup()
{
Serial.begin(9600);
// sets the digital pin as output
pinMode(buttonPin, INPUT);
// not really necessary, pins default
to INPUT anyway
digitalWrite(buttonPin, HIGH);
// turn on pullup resistors. Wire
button so that press shorts pin to ground.
}
void loop()
{
// check for button press
buttonState = digitalRead(buttonPin);
button state and store
/ Valle Thorø
// read the
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if (buttonState == LOW && lastButtonState == HIGH && blinking== fals
// check for a high to low transition
// if true then found a new button press while clock is not running
- start the clock
e){
startTime = millis();
the start time
blinking = true;
blinking while timing
delay(5);
delay to debounce switch
lastButtonState = buttonState;
buttonState in lastButtonState, to compare next time
// store
// turn on
// short
// store
}
else if (buttonState == LOW && lastButtonState == HIGH &&blinking == t
rue){
// check for a high to low transition
// if true then found a new button press while clock is running stop the clock and report
elapsedTime =
millis() - startTime;
elapsed time
blinking = false;
blinking, all done timing
// store
// turn off
// store
// routine to report elapsed time
Serial.print( (int)(elapsedTime / 1000L));
1000 to convert to seconds - then cast to an int to print
Serial.print(".");
// divide by
// print decimal
point
// use modulo operator to get fractional part of time
fractional = (int)(elapsedTime % 1000L);
// pad in leading zeros - wouldn't it be nice if
// Arduino language had a flag for this? :)
if (fractional == 0)
Serial.print("000");
// add three zero's
else if (fractional < 10)
// if fractional < 10 the 0 is
ignored giving a wrong time, so add the zeros
Serial.print("00");
// add two zeros
else if (fractional < 100)
Serial.print("0");
// add one zero
Serial.println(fractional);
// print fractional part of time
}
else{
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}
//
//
//
than
//
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// store
blink routine - blink the LED while timing
check to see if it's time to blink the LED; that is, the difference
between the current time and last time we blinked the LED is larger
the interval at which we want to blink the LED.
if ( (millis() - previousMillis > interval) ) {
if (blinking == true){
previousMillis = millis();
the last time we blinked the LED
// remember
// if the LED is off turn it on and vice-versa.
if (value == LOW)
value = HIGH;
else
value = LOW;
digitalWrite(ledPin, value);
}
else{
digitalWrite(ledPin, LOW);
LED when not blinking
}
}
// turn off
}
Brug af milis: cykelcomputer: Interrupt Triggers hver puls fra føler:
To calculate the circumference – use the formula:
circumference = 2πr
where r is the radius of the circle. Now that you have the wheel circumference, this value can be considered as our
‘fixed distance’, and therefore the speed can be calculated by measuring the elapsed time between of a full
rotation.
Your sensor – once fitted – should act in the same method as a normally-open button that is pushed every
rotation. Our sketch will measure the time elapsed between every pulse from the sensor. To do this, our example
will have the sensor output connected to digital pin 2 – as it will trigger an interrupt to calculate the speed.
(Interrupts? See chapter three). The sketch will otherwise be displaying the speed on a normal I2C-interface
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LCD module. The I2C interface is suggested as this requires only 4 wires from the Arduino board to the LCD –
the less wires the better.
Example 37.3
/*
Example 37.3 – Basic speedometer using millis();
http://tronixstuff.wordpress.com/tutorials > chapter 37
John Boxall | CC by-sa-nc
*/
#include "Wire.h" // for I2C bus LCD
#include "LiquidCrystal_I2C.h" // for I2C bus LCD module - http://bit.ly/m7K5wt
LiquidCrystal_I2C lcd(0x27,16,2); // set the LCD address to 0x27 for a 16
chars and 2 line display
float start, finished;
float elapsed, time;
float circMetric=1.2; // wheel circumference relative to sensor position (in
meters)
float circImperial; // using 1 kilometer = 0.621371192 miles
float speedk, speedm;
// holds calculated speed vales in metric and imperial
void setup()
{
attachInterrupt(0, speedCalc, RISING); // interrupt called when sensors sends
digital 2 high (every wheel rotation)
start=millis();
// setup LCD
lcd.init();
// initialize the lcd
lcd.backlight(); // turn on LCD backlight
lcd.clear();
lcd.println(" Wear a helmet! ");
delay(3000);
lcd.clear();
Serial.begin(115200);
circImperial=circMetric*.62137; // convert metric to imperial for MPH
calculations
}
void speedCalc()
{
elapsed=millis()-start;
start=millis();
speedk=(3600*circMetric)/elapsed; // km/h
speedm=(3600*circImperial)/elapsed; // Miles per hour
}
void loop()
{
lcd.setCursor(0,0);
lcd.print(int(speedk));
lcd.print(" km/h ");
lcd.print(int(speedm));
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lcd.print(" MPH
");
lcd.setCursor(0,1);
lcd.print(int(elapsed));
lcd.print(" ms/rev
");
delay(1000); // adjust for personal preference to minimise flicker
}
There isn’t that much going on – every time the wheel completes one revolution the signal from the sensor will go
from low to high – triggering an interrupt which calls the function speedCalc(). This takes a reading of millis() and
then calculates the difference between the current reading and the previous reading – this value becomes the time
to cover the distance (which is the circumference of the wheel relative to the sensor – stored in
float circMetric=1.2;
and is measured in metres). It finally calculates the speed in km/h and MPH. Between interrupts the sketch
displays the updated speed data on the LCD as well as the raw time value for each revolution for curiosity’s sake.
In real life I don’t think anyone would mount an LCD on a bicycle, perhaps an LED display would be more relevant.
In the meanwhile, you can see how this example works in the following short video clip. Instead of a bike wheel
and reed switch/magnet combination, I have connected the square-wave output from a function generator to the
interrupt pin to simulate the pulses from the sensor, so you can get an idea of how it works:
http://letsmakerobots.com/node/28278
1 Reset
2 External Interrupt Request 0
3 External Interrupt Request 1
4 Pin Change Interrupt Request
7 Watchdog Time-out Interrupt
8 Timer/Counter2 Compare Match
10 Timer/Counter2 Overflow
11 Timer/Counter1 Capture Event
18 SPI Serial Transfer Complete
19 USART Rx Complete
20 USART, Data Register Empty
21 USART, Tx Complete
/ Valle Thorø
(pin D2)
(pin D3)
0 (pins D8 to D13)
1 (pins A0 to A5)
2 (pins D0 to D7)
A
B
A
B
A
B
(INT0_vect)
(INT1_vect)
(PCINT0_vect)
(PCINT1_vect)
(PCINT2_vect)
(WDT_vect)
(TIMER2_COMPA_vect)
(TIMER2_COMPB_vect)
(TIMER2_OVF_vect)
(TIMER1_CAPT_vect)
(TIMER1_COMPA_vect)
(TIMER1_COMPB_vect)
(TIMER1_OVF_vect)
(TIMER0_COMPA_vect)
(TIMER0_COMPB_vect)
(TIMER0_OVF_vect)
(SPI_STC_vect)
(USART_RX_vect)
(USART_UDRE_vect)
(USART_TX_vect)
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22
23
24
25
26
ADC Conversion Complete
EEPROM Ready
Analog Comparator
2-wire Serial Interface (I2C)
Store Program Memory Ready
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(ADC_vect)
(EE_READY_vect)
(ANALOG_COMP_vect)
(TWI_vect)
(SPM_READY_vect)
Fra: http://www.gammon.com.au/forum/?id=11488
God og stor samling Tutorials: http://tronixstuff.com/tutorials/
#include <avr/io.h>
#include <avr/interrupt.h>
int ledPin = 8;
volatile int compAval = 10;
void setup() {
Serial.begin(9600);
sei();
TCCR2A |= 3;
TCCR2A |= (3 << 6);
TCNT2 = 0;
OCR2A = compAval;
TIMSK2 |= (1 << 1);
TIMSK2 |= 1;
TCCR2B |= 7;
}
//Enable interrupts
//Fast PWM mode 3.
//fire INT on Compare match
//initialize Timer2 to 0
//Set compare A value
//Enable CompA interrupt
//Enable OVF interrupt
//Clock select. Internal, prescale
1024~64us
{
digitalWrite(ledPin, HIGH);
}
{
compAval = compAval + 4;
if(compAval > 254)
compAval = 10;
OCR2A = compAval;
}
void loop()
{
//Serial.println(TCNT2, DEC);
}
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TCCR1B:
Bit 7
ICNC1
/ Valle Thorø
ICES1
---
---
CTC1
CS12
CS11
Bit 0
CS10
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ICNC1: Input Capture Noise Canceler; If set, the Noise Canceler on the ICP pin is activated. It will trigger the input
capture after 4 equal samples. The edge to be triggered on is selected by the ICES1 bit.
ICES1: Input Capture Edge Select;
When cleared, the contents of TCNT1 are transferred to ICR (Input Capture Register) on the falling edge of the ICP pin.
If set, the contents of TCNT1 are transferred on the rising edge of the ICP pin.
CTC1: Clear Timer/Counter 1 on Compare Match; If set, the TCNT1 register is cleared on compare match. Use this bit
to create repeated Interrupts after a certain time, e.g. to handle button debouncing or other frequently occuring events.
Timer 1 is also used in normal mode, remember to clear this bit when leaving compare match mode if it was set.
Otherwise the timer will never overflow and the timing is corrupted.
http://www.let-elektronik.dk/tutorials
en samling links til Jeremy Bloms videos:
Se: http://harperjiangnew.blogspot.dk/2013/05/arduino-using-atmegas-internal.html
http://tom-itx.dyndns.org:81/~webpage/abcminiuser/articles/avr_timers_index.php
CTC mode: http://maxembedded.com/2011/06/28/avr-timers-timer1/
http://www.youtube.com/watch?v=CRJUdf5TTQQ
http://www.uchobby.com/index.php/2007/11/24/arduino-interrupts/
http://www.protostack.com/blog/2010/09/timer-interrupts-on-an-atmega168/
http://www.instructables.com/id/Arduino-Timer-Interrupts/step2/Structuring-Timer-Interrupts/
http://www.engblaze.com/microcontroller-tutorial-avr-and-arduino-timer-interrupts/
http://arduino-info.wikispaces.com/Timers-Arduino
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