Help with timer

[Tjaalie]

Hello,

For my OS i made i timer with a wait function but its hangs.
The code for the function is like this:

Code: Select all

void TimerWait(int ticks)
{
     //Vars
     int WaitTime = Timer + ticks;
     
     //Kijk of we niet te ver gaan
     if (WaitTime >= 1000)
     {
        WaitTime -= 1000;
     }
     
     //Wait
     while (Timer < WaitTime);
}

I dont know why it hangs its just so n00b but can anybody tell me why?[/code]

[rexlunae]

I dont know why it hangs its just so n00b but can anybody tell me why?

It probably hangs because of that loop at the end. The code you gave us does not contain anything that causes that loop to end. What is Time? Is it a global variable updated on an interrupt?

[Tjaalie]

The timer variable works like:

Code: Select all

void HandleTimer(struct regs* r)
{
     Timer++;

     if (Timer >= 1000)
     {
          Timer = 0;
     } 
}

So can you tell me whats wrong with the loop?
The i know the HanleTimer function get called cause when i put an print function in it it prints the text many times so its works. What do i do wrong?

[Anton]

So can you tell me whats wrong with the loop?

Do you have optimization turned on? If you do turn it off.
Also make the variable Timer volatile

The i know the HanleTimer function get called cause when i put an print function in it it prints the text many times so its works.

This is wrong, since if you remove an print function, the compiler might optimize out the code.
Anton.

[rexlunae]

Do you have optimization turned on? If you do turn it off.
Also make the variable Timer volatile

All that should be necessary is declaring it volatile. Turning off optimizations should not be necessary. I wonder what the interrupt flag is set to when he enters the loop though. If it is not allowing interrupts, the Timer variable won't get changed.

[Tjaalie]

thanx i only had to volatile it but what does
volatile do. can any body explain that why its working
now and not without it?

[bregma]

thanx i only had to volatile it but what does
volatile do. can any body explain that why its working
now and not without it?

"volatile" effectively tells the compiler that the memory location may be changed without the compiler's knowledge, so it won't try to use a cached value in a register but instead always retrieve it from memory.

--
smw

[Legend]

Or more general perhaps, it protectes the variable from optimizations.

[jcmatias]

How do you use this code?
Is this a ISR ?
If is the case , remember that the ISR return is IRET.

[DruG5t0r3]

That Timer function is far from being reliable. Lets say you have a 1mhz CPU and another one with 2 billion teraflops....(OK i'm exagerating)... Which one will go out of the loop first?...

I recommend to rely on IRQ 0 , I believe it's the only reliable timer you have on a x86 system.

[Tjaalie]

this timer uses the irq 0