Communication between Tasks

[Gerald]

hi,

i have 2 taks, on task is measuring some stuff and the other is doing some stuff depending on the state variable in task1!
could i just use a global variable between the 2 task? the first tasks sets the variable and the second task is reading the variable!?
or any other solution?
i dont want to use a message or stuff like that...because i dont want to block for a certain time in task2!!!!!!!

[This message has been edited by Gerald (edited April 16, 2008).]

[aek]

There's nothing fundamentally wrong with using global variables ... but if you do so, you should declare said variables as static within one module, and provide a function-based interface to them (E.g. read_gvars(), write_gvars(), etc.). This takes more code, but is considered cleaner and safer.

The trouble with such an approach in a multitasking system is that you cannot use changes in said (global) vars to trigger the running of the dependent task -- hence no real synchronicity.

Note that if you have bit-sized vars (flags, essentially) then you maybe can use an eFlag instead, and yu could block on the eFlag. You could have one eFlag bit be "hit" periodically by a timer to trigger a minimum "repeat rate" for the dependent task.

------------------

[Gerald]

do you see any problems here?
i set a breakpoint to OSSetEFlag(VOLTAGE_EFLAG_P, VALID); but it never came to the breakpoint, then i stopped debugging and continued and it stops at the breakpoint...do you understand that?

code:

---

void TaskADC()
{
	static OStypeErr err;
	static unsigned int adc_value = 0;
	static unsigned int channelindex = 0;
	static unsigned int voltage = 0;
	// enable adc measurement
	bit_set(DDRC, PC1);
	bit_set(PORTC, PC1);
		 	
	init_adc();
	
	for(;    ;)
	{
		// start convertion
		start_adc();
		// wait for convertion finished
		while(ADCSRA & (1<<ADSC));
		adc_value += ((ADCH << 2) | (ADCL >> 6));
		
		if (channelindex < (HISTORY_SIZE - 1))
		{
			channelindex++;
		}
		else 
		{
			if(HISTORY_SIZE == 16)
			{
				voltage = (adc_value >> 4);
				            // 9V            // 16V 
				if(voltage >= 512 && voltage <= 909)
					OSSetEFlag(VOLTAGE_EFLAG_P, VALID);
				adc_value = 0;
				channelindex = 0;
			}
		}
		
		OS_Delay(1);
	}
}

void TaskFunctionLogic()
{
	static OStypeErr err;
	static OStypeMsgP msgP;
	for(;    ;)
	{	
		OS_WaitEFlag(VOLTAGE_EFLAG_P, VALID, OSANY_BITS, OSNO_TIMEOUT);
			
		// ... do some stuff if coltage is VALID
		OSClrEFlag(VOLTAGE_EFLAG_P, INVALID);
	}
}
main.c:
// start all tasks....
OSCreateEFlag(VOLTAGE_EFLAG_P, VOLTAGE_EFLAG_CB_P, INVALID);
my include files:
-----------------
-----------------
salvocfg.h:
#define OSEVENTS                5
#define OSEVENT_FLAGS           1
#define OSMESSAGE_QUEUES        0
#define OSTASKS                 5
os.h:
#define MSG_...			OSECBP(1)
#define MSG_...		OSECBP(2)
#define MSG_...	OSECBP(3)
#define MSG_... OSECBP(4)
#define VOLTAGE_EFLAG_P OSECBP(5)

#define VOLTAGE_EFLAG_CB_P OSEFCBP(1)
#define VALID 0x01
#define INVALID 0x02
#define TASK_FUNCTIONLOGIC_P			OSTCBP(1)	/*  ""  #1        */
#define TASK_...					OSTCBP(2)	/*  ""  #2        */
#define TASK_...				OSTCBP(3)	/*  ""  #3        */
#define TASK_...				OSTCBP(4)	/*  ""  #4        */
#define TASK_ADC_P						OSTCBP(5)	/*  ""  #4        */
#define PRIO_FUNCTIONLOGIC				10			/*  ""            */
#define PRIO_...					10	        /*  ""            */
#define PRIO_...					10			/*  ""            */
#define PRIO_...					10			/*  ""            */
#define PRIO_ADC						10			/*  ""            */

---

You could have one eFlag bit be "hit" periodically by a timer to trigger a minimum "repeat rate" for the dependent task. ?????

[This message has been edited by Gerald (edited April 17, 2008).]

[This message has been edited by aek (edited April 17, 2008).]

[aek]

It's best to set a breakpoint on a NOP() or such -- some debuggers don't break well on Salvo API calls, some of which are macros.

To me, it looks like that code should work.

However, in general what I do is separate the ADC acquisition from any sampled voltage tests. I.e. I use one task to initialize the adc and average the outputs, and another periodic task to examine the results and act on them. But your approach should work as well.

------------------

[Gerald]

// 9V // 16V
if(voltage >= 512 && voltage <= 909)
OSSetEFlag(VOLTAGE_EFLAG_P, VALID);
else
OSSetEFlag(VOLTAGE_EFLAG_P, INVALID);

void TaskFunctionLogic()
{
static OStypeErr err;
static OStypeMsgP msgP;

for(;
{
OS_WaitEFlag(VOLTAGE_EFLAG_P, VALID, OSANY_BITS, OSNO_TIMEOUT);

// ... do some stuff if coltage is VALID

OSClrEFlag(VOLTAGE_EFLAG_P, INVALID); // also did with: OSClrEFlag(VOLTAGE_EFLAG_P, INVALID);
}
}

at the first time i the eflag is invalid OS_WaitEFlag blocks! thats ok
then i set the eflag to valid...the OS_WaitEFlag doesnt block...ok too!
then i change the eflag to invlid...but the OS_WaitEFlag doesnt block
why not?

[This message has been edited by Gerald (edited April 20, 2008).]