Routine calling routine...

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August 24th, 2012, 02:32 PM

dtvonly

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Routine calling routine...

Hi. Please see the code below:

Code:

void task1(void);
void task2(void);

void main()
{
	task1();

	while(1);
}		

void task1()
{
	static unsigned int i=0;
	while(1)
	{
		NOP();
		i++;
		if(i>254)
			while(1);
		task2();
	}
}

void task2()
{
	static unsigned int j=0;
	while(1)
	{
		NOP();
		j++;
		if(j>254)
			while(1);
		task1();
	}
}

The problem: both i and j only got to 29 then the program ended.
Why?

August 24th, 2012, 02:45 PM

salem

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What's to say?

None of the loops do anything useful.

It's just task1() task2() task1() task2() until you run out of stack and the whole thing just blows up.

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August 24th, 2012, 06:23 PM

dtvonly

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Join Date: Jun 2012

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Time spent in forums: 30 m
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Quote:

Originally Posted by salem

What's to say?

None of the loops do anything useful.

It's just task1() task2() task1() task2() until you run out of stack and the whole thing just blows up.

The whole reason for what I am doing is to "simulate" what RTOS are doing. Most RTOS have while(1) in their task routines within which other routine(s) are called in this simular way. So if it is a stack issue, how is that resolved?

August 24th, 2012, 11:42 PM

salem

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Join Date: Jun 2005

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Time spent in forums: 2 Months 3 Weeks 2 Days 19 h 21 m 53 sec
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Well in an RTOS (or any OS for that matter), tasks are not responsible for switching between themselves.

Here, spawn() creates a separate stack, and the named function is an entry point.
The schedule() function is then called to start the first task, and thereafter periodically switch between tasks.
Note: These are both imaginary functions - you can't just write this and expect it to work, without providing a lot of implementation.

Code:

void task1(void);
void task2(void);

void main()
{
	spawn(task1);
	spawn(task2);
	schedule();
}		

void task1()
{
	static unsigned int i=0;
	while(1)
	{
		NOP();
		i++;
	}
}

void task2()
{
	static unsigned int j=0;
	while(1)
	{
		NOP();
		j++;
	}
}

If you want a reasonable simulation without a lot of effort on your part, then look at threads.

Routine calling routine...

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