[SOLVED] Error (timer0 AVR microcontroller)

Don_dody · Dec 18, 2012

I want to make 1s delay using TIMER0 and Here is the code:

Code:

#include <mega8535.h>

interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{
delay = delay + 1
}

void main(void)
{
// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: 3.906 kHz
// Mode: Normal top=FFh
TCCR0=0x05;
TCNT0=0xD9;
// Timer0 enable
TIMSK=0x01;
// Global enable interrupts
#asm("sei")

while (1)
      {
       delay(100);   //(100*10ms=1000ms)
      };
}

void delay(int delay_ms)
{
   TCNT0=0xD9;  //timer interval= 10 ms
   delay=0
   while(delay<=delay_ms)
   {
    }
}

I got error messages as follow:
1. undefined symbol 'delay'
2. the expression must be a modifiable lvalue

Whats wrong here?

alexan_e · Dec 18, 2012

You can't use delay before declaring the delay function.

either move the delay function before main or add the prototype of the delay function before main so that the compiler is informed about it

Code:

void delay(int delay_ms);

Don_dody · Dec 18, 2012

OK, I've modified it become:

Code:

#include <mega8535.h>

void delay(int delay_ms)
{
   TCNT0=0xD9;  //timer interval = 10 ms
   delay=0
   while(delay<=delay_ms)
   {
    }
}

interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{
delay = delay + 1
}



void main(void)
{
// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: 3.906 kHz
// Mode: Normal top=FFh
TCCR0=0x05;
TCNT0=0xD9;
// Timer0 enable
TIMSK=0x01;
// Global enable interrupts
#asm("sei")

while (1)
      {
       delay(100);   //(100*10ms=1000ms)
      };
}

However I still got error:
Error: the expression must be a modifiable lvalue

alexan_e · Dec 18, 2012

delay represents in your code a function that doesn't return any result,
You cant use

Code:

while(delay<=delay_ms)
//or
delay = delay + 1

Don_dody · Dec 18, 2012

so what should I use? any suggestions?

alexan_e · Dec 18, 2012

add a global variable and use that

Don_dody · Dec 18, 2012

Still error hmmm

Well do you have any example or references to make delay using timer?

alexan_e · Dec 18, 2012

Here is an example that uses a variable to count interrupts https://extremeelectronics.co.in/avr-tutorials/avr-timers-an-introduction/

Don_dody · Dec 24, 2012

I got it.
Now I can make a simple blinking led with 1s delay using timer.

Thanks.

[SOLVED] Error (timer0 AVR microcontroller)

Don_dody

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