Coming from this question and I just wonder How to calculate maximum time that an Atmega328 timer can give us before trigger an interrupt? I want it to trigger every hour or so in my project but due to the fact that C integer and OCR1A register has some limitation in size it seems far fetch to get an hour from it.
Is it possible to modify my last question code to get some hour delay?
It should be, depending on the frequency of your microcontroller and the prescaler you're going to use.
Atmega 328P is 20 MHz. So if you take 20,000,000/1024 = 19531. Thats the number of cycles in 1 second.
You can find this in the data sheet for a 16 Bit Timer:
volatile uint8_t count = 0;
void set_up_timer() {
TCCR1B = (1 << WGM12); // from the datasheet
OCR1A = 19531; // number of ticks in a second
TIMSK1 = (1 << OCIE1A); // from the data sheet
TCCR1B |= (1 << CS12) | (1 << CS10);
You can set a global variable, and increment it in the ISR Routine until the desired value is achieved. Something along the lines of:
ISR(TIMER1_COMP1_VECT) {
counter++;
if(counter >= 3600) {
// do whatever needs to be done
}
The comment by Jabberwocky translates to this code (based on the other question to which your have posted the link)
... includes
/* In milliseconds */
const unsigned int ISR_QUANTUM = 1000; // once in a second
/* How much time should pass (1 hours = 3600 seconds = 3600 * 1000 ms */
const unsigned long LONG_TIME_INTERVAL = 1000 * 3600;
volatile unsigned long time_counter;
void once_an_hour() {
... do what needs to be done
}
int main(void) {
... setup your timer interrupt (high-precision, "short-range")
// reset your 'seconds' time counter
time_counter = 0;
while (1)
{
// busy-wait for time counter passing
if (time_counter > LONG_TIME_INTERVAL) {
// reset global timer
time_counter = 0;
once_an_hour();
}
// do other things
...
}
}
ISR (TIMER1_COMPA_vect)
{
// action to be done every Xms - just increment the time_counter
time_counter += ISR_QUANTUM;
}
This way you just increment a "global" time counter in a "local" interrupt handler.
Related
I'm creating part of a program right now for a personal project. This is my first year ACTUALLY coding and have been studying for hours to understand many concepts so please be nice and try not to be rude as others have...
The project of mine is an AVRDUDE using a chip called ATMEGA328P in a program called Microchip studios.
[This project is having 3 LED count every time a switch is pressed, I should have them count continuously and change to the next number every second using a TIMER 1.
**counting in binary from 0-8 then rolling over **
I need some help on one aspect of it which is using interrupts after I have already created a blinking LED to use a TIMER0 instead of delays.
I have made my fourth LED flash at 5Hz which is the blinking part of my code include below at the end of this question.
Now the problem I am running into is trying to create interrupts for the 3 LEDS count every time a switch is pressed, I should instead have them continually count, changing to the next number approximately every second, using TIMER1.]
This is my code for the project
Again please be nice and at least lead me in some type of direction...
#include <avr/io.h>
#include <avr/interrupt.h>
#define F_CPU 1000000UL
int global = 0 ;
volatile uint8_t overflow0; // Variable for counting overflows for first timer
volatile uint8_t overflow1; // Variable for counting overflows for second timer
void FirstTimer() // Initialize Timer 1
{
TCCR0B |= (1<<CS02) | (1<<CS00); // Prescaler of 1024
TCNT0 = 0;
}
void SecondTimer() //Initialize Timer 2
{
TCCR1B |= (1<<CS11) | (1<<CS10);
TCNT1 = 0;
}
int main(void)
{
DDRB |= (1 << DDB0);
FirstTimer(); // Calling timer 1 and 2 initialization
SecondTimer();
while (1)
{
{
if (TCNT0 >= 195) // Amount of ticks needed
{
PORTB ^= (1 << PORTB0); //LED on
TCNT0 = 0; //Reset counter
}
}
{
if (TCNT1 >= 15625) // Ticks needed
{
TCNT1 = 0; // Timer reset
}
}
}
}
An approach you could use is keeping a count variable (unsigned char - assuming 8 bit register width) and in your Timer ISR simply increment the count and write that value to the output register. Once count > 8 set to zero.
Configure the Timer mode to trigger on overflow w/ reset to zero.
Then you do some basic math using the clock speed and timer ceiling (overflow value) to calculate the frequency you want the overflow ISR to occur (increment the LED count values).
Note that for this to work the LEDs need to be on the first 3 pins.
i.e.
P1.0 = LED1
P1.1 = LED2
P1.2 = LED3
...
If not connected like this then you can still make it work with additional bit manipulation (shifts and masks).
There is Attiny85, with an internal clock source at 8 MHz.
I am trying to implement a microsecond timer based on the hardware timer timer0.
What is my logic:
Since the clock frequency is 8 MHz and the prescaler is off, the time of one clock cycle will be about 0.1us (1/8000000).
Initially, the timer overflows and causes interruptions when passing 0 ... 255, it takes more than 0.1us and is inconvenient for calculating 1μs.
To solve this, I thought about the option to change the initial value of the timer instead of 0 to 245. It turns out that in order to get to the interruption, you need to go through 10 clock cycles, which takes about 1us in time.
I load this code, but the Attiny LED obviously does not switch for about 5 seconds, although the code indicates 1 second (1000000us).
Code:
#include <avr/io.h>
#undef F_CPU
#define F_CPU 8000000UL
#include <avr/interrupt.h>
// Timer0 init
void timer0_Init() {
cli();
//SREG &= ~(1 << 7);
// Enable interrupt for timer0 overflow
TIMSK |= (1 << 1);
// Enabled timer0 (not prescaler) - CS02..CS00 = 001
TCCR0B = 0;
TCCR0B |= (1 << 0);
// Clear timer0 counter
TCNT0 = 245;
sei();
//SREG |= (1 << 7);
}
// timer0 overflow interrupt
// 1us interval logic:
// MCU frequency = 8mHz (8000000Hz), not prescaler
// 1 tick = 1/8000000 = 100ns = 0.1us, counter up++ after 1 tick (0.1us)
// 1us timer = 10 tick's => 245..255
static unsigned long microsecondsTimer;
ISR(TIMER0_OVF_vect) {
microsecondsTimer++;
TCNT0 = 245;
}
// Millis
/*unsigned long timerMillis() {
return microsecondsTimer / 1000;
}*/
void ledBlink() {
static unsigned long blinkTimer;
static int ledState;
// 10000us = 0.01s
// 1000000us = 1s
if(microsecondsTimer - blinkTimer >= 1000000) {
if(!ledState) {
PORTB |= (1 << 3); // HIGH
} else {
PORTB &= ~(1 << 3); // LOW
}
ledState = !ledState;
blinkTimer = microsecondsTimer;
}
}
int main(void)
{
// Set LED pin to OUTPUT mode
DDRB |= (1 << 3);
timer0_Init();
while (1)
{
ledBlink();
}
}
Attiny85 Datasheet
What could be the mistake? I have not yet learned how to work with fuses, so I initially loaded the fuses at 8 MHz through the Arduino IDE, and after that I already downloaded the main code (without changing the fuses) through AVRDUDE and Atmel Studio.
And another question, should I check the maximum value when updating my microsecond counter? I know that in Arduino, the micro and millis counters are reset when they reach the maximum value. For example, if I do not clear the TimerMicrosecond variables variable and it exceeds the size of the unsigned long, will it crash?
As pointed out by #ReAI, your ISR does not have enough time to run. Your ISR will take more than 1 microsecond to execute and return, so you always are missing interrupts.
There are other problems here too. For example, your microsecondsTimer variable is accessed in both the ISR and the foreground and is a long. long variables are 4 bytes wide and so are not updated atomically. It is possible, for example, that your foreground could start reading the value for microsecondsTimer and then in the middle of the read, the ISR could update some of the unread bytes, and then when the foreground starts again it will end up with a mangled value. Also, you should avoid messing with the count register since updating it can miss ticks unless you are very careful.
So how could you implement a working uSec timer? Firstly you'd like to call the ISR as infrequently as possible, so maybe pick the largest prescaller you can get get the resolution that you want and only ISR on overflow. In the case of the ATTINY85 Timer0, you can pick /8 prescaller which gets you one tick of the timer per microsecond with an 8Mhz system clock. Now your ISR only runs once every 256 microseconds and when it runs, it need only increment a "microseconds * 256" counter in each call.
Now to read the current microseconds in the foreground, you can get the number of microseconds mod 256 by directly reading the count register, and then read the "microseconds * 256" counter and multiply this by 256 and add that the counter and you'll have the full count. Note that you will need take special precautions to make sure your reads are atomic. You can do this either by carefully turning off the interrupts, quickly reading the values, and then turning the interrupts back on (save all the math for when interrupts are back on), or looping on the read values to make sure you get two full reads in a row that are the same (time means that have not updated while you were reading them).
Note that you can check out the source code to Arduino timer ISR for some insights, but note that theirs is more complicated because it can handle a wide range of tick speeds whereas you are able to keep things simple by specifically picking a 1us period.
why you didn't use pre-scaler ?!
your code need a relly relly big delay intervall(1 sec it's huge time according to cpu speed) .... so it's not wisdom choose to interrupt microcontroller every 1 us !!.. so it will be great if we could slow down your microcontroller clock and make interrupt for example every 1 ms
calculation
the microcontroller clock speed is 8 mega Hz so if we chose the preScaller to 64 then the timer clock will be 8MHz/64=125 KHz so that mean each tik (timer clock) time will be 1/125KHZ=8 us
so if we like to have inturrpt every 1ms then we need 125 tik
modify code
try this code it's more clear to understand
#undef F_CPU
#define F_CPU 8000000UL
#include <avr/io.h>
#include <avr/interrupt.h>
volatile int millSec;
void timer0_Init();
void toggleLed();
int main(void)
{
// Set LED pin to OUTPUT mode
DDRB |= (1 << 3);
timer0_Init();
millSec = 0; // init the millsecond
sei(); // set Global Interrupt Enable
while (1)
{
if(millSec >= 1000){
// this block of code will run every 1 sec
millSec =0; // start count for the new sec
toggleLed(); // just toggle the led state
}
// Do other backGround jobs
}
}
//#####Helper functions###########
void timer0_Init() {
// Clear timer0 counter
TCNT0 = 130; //255-125=130
// Enable interrupt for timer0 overflow
TIMSK = (1 << 1);
// set prescaler to 64 and start the timer
TCCR0B = (1<<CS00)|(1<<CS01);
}
void toggleLed(){
PORTB ^= (1 << 3); // toggle led output
}
ISR(TIMER0_OVF_vect) {
// this interrupt will happen every 1 ms
millSec++;
// Clear timer0 counter
TCNT0 = 130;
}
Sorry, i am late but i have got some suggestions. If you calculate the Timer0 with prescaler 1, the timer is counting up every 125ns. It is not possible to reach 1 us without a small divergence. But if you use prescaler 8 you reach exactly 1 us. I actually do not have your hardware but give this a try:
#ifndef F_CPU
#define F_CPU 8000000UL
#else
#error "F_CPU already defined"
#endif
#include <avr/io.h>
#include <avr/interrupt.h>
volatile unsigned int microsecondsTimer;
// Interrupt for Timer0 Compare Match A
ISR(TIMER0_COMPA_vect)
{
microsecondsTimer++;
}
// Timer0 init
void timer0_Init()
{
// Timer0:
// - Mode: CTC
// - Prescaler: /8
TCCR0A = (1<<WGM01);
TCCR0B = (1<<CS01);
OCR0A = 1;
TIMSK = (1<<OCIE0A)
sei();
}
void ledBlink() {
static unsigned int blinkTimer;
if(microsecondsTimer >= 1000)
{
microsecondsTimer = 0;
blinkTimer++;
}
if(blinkTimer >= 1000)
{
PORTB ^= (1<<PINB3);
blinkTimer = 0;
}
}
int main(void)
{
// Set LED pin to OUTPUT mode
DDRB |= (1 << PINB3);
timer0_Init();
while (1)
{
ledBlink();
}
}
If you are using internal clock of attiny it may be divied by 8. To disable the clock division you have to disable the prescaler within 4 clock cycles (atomic operation):
int main(void)
{
// Reset clock prescaling
CLKPR = (1<<CLKPR);
CLKPR = 0x00;
// ...
Please try this solution an give feedback if it is working. Maybe you can verify it with an oscilloscope...
Notice that operations with unsigned long needs more than 1 clock cycle to handle on an 8 bit microcontroller. Maybe it would be better to use unsigned int or unsigned char. The main loop also should not contain lots if instructions. Otherwise error correction of microsecond timer has to be implemented.
I want to configure timer1 of PIC24F16KA102 to count it. The clock source must be the internal clock of 8 MHz. I configured the register T1CON and set on high level the bit TON to start the timer. Timer1 is set to go in overflow every 100 us, then with a while cycle I wille increase the variable count. I'am not understanding because timer1 don't work, I observed that it does not increase. Why?
#include <xc.h>
#include "config.h"
int count = 0;
void main(void) {
TRISB = 0;
T1CON = 0; //TRM1 stopped, internal clock source, prescaler 1:1
_TON = 1;
TMR1 = 65135; //overflow of TM1 every 100 us (400 counts)
while (1) {
if (TMR1 == 65535) {
count++; // increase every 100 us
TMR1 = 65135;
}
}
}
Try setting the Timer 1 period register (PR1) and using an interrupt rather than trying to catch and reload TMR1 on its final count. You're trying to catch TMR1 on EXACTLY 65535, and that will almost never work because once TMR1 hits 65535, it's just going to overflow and begin counting from 0 again.
EDIT: Of course, this assumes it counts at all. I don't know what the behavior of a timer is when you leave the period register at 0. It may simply count to it's maximum of 65535 then reset to 0, or it may never count at all and continuously load PRx into TMRx since they match at 0
PRx is meant to define the period you want for a given timer, in this case 100uS. PR1 = 400. Once TMR1 = PR1, the timer will reset itself automatically and raise an interrupt to alert you that the timer has elapsed.
volatile unsigned int count = 0; //Vars that change in an ISR should be volatile
PR1 = 400; //Set Period for Timer1 (100us)
T1CON = 0x8000; //Enable Timer1
IEC0bits.T1IE = 1; //Enable Timer1 Interrupt
IPC0bits.T1IP = 0b011;
Pair this with an ISR function to increment count whenever the timer elapses:
void __attribute__ ((interrupt,no_auto_psv)) _T1Interrupt (void)
{
count++;
IFS0bits.T1IF = 0; //Make sure to clear the interrupt flag
}
You could also try something like this without any interrupts:
void main(void){
unsigned int count = 0;
TMR1 = 0;
T1CON = 0x8000; //TON = 1
while(1){
if (TMR1 >= 400){
count++;
TMR1=0;
}
}
}
However I would recommend using the PR register and an ISR. This is what it's meant to do.
EDIT: I would also recommend reading the PIC24F Reference Manual on timers:
Here
I am trying to understand this piece of code, What I am not able to understand is how the interrupt routine works as the OCR1A is getting updated. I am using AVR series of controller to run this code.
void TimerInit(void)
{
DISABLE_TIMER_INT; // Disable timer interrupt
m_nGlobalTime = 0; // Reset system time
OCR1A += TICKS_PER_MSECOND; // Set first clock period
TCCR1A = 0;// Set TimerMode to Normal
TCCR1B |= (1 << CS10);// ClckIo, no pre-scaler; set TimerMode
ENABLE_INTERRUPTS;
ENABLE_TIMER_INT;// Enable send timer interrupt (1 ms)
}
ISR( TIMER1_COMPA_vect) {
uint16_t nTemp;
nTemp = TCNT1; // Get current time
nTemp -= OCR1A; // Subtract interrupt time
if (nTemp < (TICKS_PER_MSECOND / 2))// If more than half period left
{
OCR1A += (TICKS_PER_MSECOND);// Add Offset to OCR1A relative
}
else
{
OCR1A = TCNT1 + (TICKS_PER_MSECOND);// Set OCR1A to 1 ms absolute
}
m_nGlobalTime++;
}
The usual way to get an output compare interrupt to fire at a regular interval is to add a constant amount to the OCR1A. This is happening at
OCR1A += (TICKS_PER_MSECOND);
For some reason, the writer added some extra logic to handle bad luck. Perhaps, the period is too short, or maybe the OC interrupt may be delayed due to some other interrupt running.
If these cases were to occur, then the next OC interrupt would not occur TICKS_PER_MSECOND later than the last, but rather TICKS_PER_MSECOND plus an entire cycle of the counter. That is, the correct time would be missed, as the OC register would be set to a number after the number has been passed.
This code is an attempt to correct for this situation. That being said, I'm not sure it works correctly. The potential problem is that nTemp is unsigned, so the < comparison might not do what the writer expects.
I am using MSP430F5418 with IAR EW 5.10.
I want to use Timer B in up mode.
I want to use two interrupts.
TimerB0(1 ms) and TimerB1(1 second).
My Configuration is
TBCTL = MC__UP + TBSSEL__ACLK + TBCLR;
TB0CCTL0 = CCIE;
TB0CCR0 = 32;
TB0CCTL1 = CCIE;
TB0CCR1 = 32768;
On the ISR I just toggled two pins.
But only the pin for TB0CCR0 is toggling.
My Pin Configurations are correct.
Can anyone tell me why??
I suppose your problem is the timer period.
MC__UP Up mode: Timer counts up to TBxCL0
So your timer TBxR will reset to 0 when it reaches TBxCL0 which seems to be the value TB0CCR0.
So it can never reach the value of 32768.
You could switch TB0CCR0 with TB0CCR1, so your period will be 1 second.
And to get your 1ms interrupt you need to increment your TB0CCR1 each time.
INTERRUPT ISR_1MS()
{
TB0CCR1 = (TB0CCR1 + 32) & 0x7FFF;
}
But normally you don't need a second timer for a second intervall.
You could simply count 1000 times your 1ms intervall.
INTERRUPT ISR_1MS()
{
ms_count++;
if (ms_count >= 1000)
{
ms_count=0;
// Do your second stuff
}
}
And if you need more and different intervalls, you could change to another model.
To a system clock time and check only against this time.
volatile unsigned int absolute_time=0;
INTERRUPT ISR_1MS()
{
absolute_time++;
}
unsigned int systime_now(void)
{
unsigned int result;
di();
result = absolute_time;
ei();
return result;
}
uint8_t systime_reached(unsigned int timeAt)
{
uint8_t result;
result = (systime_now() - timeAt ) < 0x1000;
return result;
}