[Xenomai-help] Hello world with questions

[Xenomai-help] Hello world with questions

[roland Tollenaar]

Hi,

I have copy-pasted the trivial app into the body of this mail. To
understand what is
going on I have sprinkled and garnished it with questions.


[These are standard headers I presume]
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <sys/mman.h>


[These are xenomai headers. What libraries must be linked in with them?]
#include <native/task.h>
#include <native/timer.h>

[I see this macro is called later as an argument. What is its function?]
RT_TASK demo_task;

/* NOTE: error handling omitted. */

void demo(void *arg)
{

       	RTIME now, previous;

	/*
	 * Arguments: &task (NULL=self),
	 *            start time,
	 *            period (here: 1 s)
	 */
	rt_task_set_periodic(NULL, TM_NOW, 1000000000);

	previous = rt_timer_read();

	while (1) {
		rt_task_wait_period(NULL);
		now = rt_timer_read();

		/*
		 * NOTE: printf may have unexpected impact on the timing of
		 *       your program. It is used here in the critical loop
		 *       only for demonstration purposes.
		 */
		printf("Time since last turn: %ld.%06ld ms\n",
		       (long)(now - previous) / 1000000,
		       (long)(now - previous) % 1000000);
		       previous = now;
	}
}


[The purpose of this function eludes me ?]
void catch_signal(int sig)
{
}

int main(int argc, char* argv[])
{

[What is happening here?]
	signal(SIGTERM, catch_signal);
	signal(SIGINT, catch_signal);

[Does this mean I cannot access global variables if this program is
running in a thread? That would be a disastrous limitation!]
	/* Avoids memory swapping for this program */
	mlockall(MCL_CURRENT|MCL_FUTURE);

	/*
	 * Arguments: &task,
	 *            name,
	 *            stack size (0=default),
	 *            priority,
	 *            mode (FPU, start suspended, ...)
	 */
[I presume this sets the function "demo" as a real-time task?]
	rt_task_create(&demo_task, "trivial", 0, 99, 0);

	/*
	 * Arguments: &task,
	 *            task function,
	 *            function argument
	 */
	rt_task_start(&demo_task, &demo, NULL);
[Is RTASK a task label? What happens if there are more than 1 task to
run in separate threads?]

[How is the loop broken to get to this part of the program?]
	pause();

	rt_task_delete(&demo_task);
}


Kindly,

Roland.

Re: [Xenomai-help] Hello world with questions

[Jan Kiszka]

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roland Tollenaar wrote:
> Hi,
> 
> I have copy-pasted the trivial app into the body of this mail. To
> understand what is
> going on I have sprinkled and garnished it with questions.
> 
> 
> [These are standard headers I presume]
> #include <stdio.h>
> #include <signal.h>
> #include <unistd.h>
> #include <sys/mman.h>

Jep.

> 
> 
> [These are xenomai headers. What libraries must be linked in with them?]
> #include <native/task.h>
> #include <native/timer.h>

-lnative, see examples.

> 
> [I see this macro is called later as an argument. What is its function?]
> RT_TASK demo_task;

It's a type in fact. Actually, this is bad style, derived from the
original RTAI API mess. I think we should establish something like
rt_task_t etc. on the long-term for the Xenomai native skin, keeping the
current names only for legacy code (Philippe?).

> 
> /* NOTE: error handling omitted. */
> 
> void demo(void *arg)
> {
> 
>           RTIME now, previous;
> 
>     /*
>      * Arguments: &task (NULL=self),
>      *            start time,
>      *            period (here: 1 s)
>      */
>     rt_task_set_periodic(NULL, TM_NOW, 1000000000);
> 
>     previous = rt_timer_read();
> 
>     while (1) {
>         rt_task_wait_period(NULL);
>         now = rt_timer_read();
> 
>         /*
>          * NOTE: printf may have unexpected impact on the timing of
>          *       your program. It is used here in the critical loop
>          *       only for demonstration purposes.
>          */
>         printf("Time since last turn: %ld.%06ld ms\n",
>                (long)(now - previous) / 1000000,
>                (long)(now - previous) % 1000000);
>                previous = now;
>     }
> }
> 
> 
> [The purpose of this function eludes me ?]
> void catch_signal(int sig)
> {
> }

POSIX signal handling (not Xenomai-related): makes pause() below return
when some of the caught signals arrive.

> 
> int main(int argc, char* argv[])
> {
> 
> [What is happening here?]
>     signal(SIGTERM, catch_signal);
>     signal(SIGINT, catch_signal);

# man signal

> 
> [Does this mean I cannot access global variables if this program is
> running in a thread? That would be a disastrous limitation!]
>     /* Avoids memory swapping for this program */
>     mlockall(MCL_CURRENT|MCL_FUTURE);

??? There is no such limitation. It's the plain thread programming model
like with normal pthreads.

# man mlockall

> 
>     /*
>      * Arguments: &task,
>      *            name,
>      *            stack size (0=default),
>      *            priority,
>      *            mode (FPU, start suspended, ...)
>      */
> [I presume this sets the function "demo" as a real-time task?]
>     rt_task_create(&demo_task, "trivial", 0, 99, 0);

No, it just creates that task object, the function is set below.

> 
>     /*
>      * Arguments: &task,
>      *            task function,
>      *            function argument
>      */
>     rt_task_start(&demo_task, &demo, NULL);
> [Is RTASK a task label? What happens if there are more than 1 task to
> run in separate threads?]

RT_TASK is the type of a task /descriptor/ (like a file descriptor or
pthread_t). You can have more tasks by playing with more descriptors.

> 
> [How is the loop broken to get to this part of the program?]
>     pause();

see above

> 
>     rt_task_delete(&demo_task);
> }
> 
> 
> Kindly,
> 
> Roland.
> 

HTH,
Jan


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Re: [Xenomai-help] Hello world with questions

[Roland Tollenaar]

Hi,

Thanks. Will go through this and hopefully slowly start making sense of it.

Roland



Jan Kiszka wrote:
> roland Tollenaar wrote:
>> Hi,
>>
>> I have copy-pasted the trivial app into the body of this mail. To
>> understand what is
>> going on I have sprinkled and garnished it with questions.
>>
>>
>> [These are standard headers I presume]
>> #include <stdio.h>
>> #include <signal.h>
>> #include <unistd.h>
>> #include <sys/mman.h>
> 
> Jep.
> 
>>
>> [These are xenomai headers. What libraries must be linked in with them?]
>> #include <native/task.h>
>> #include <native/timer.h>
> 
> -lnative, see examples.
> 
>> [I see this macro is called later as an argument. What is its function?]
>> RT_TASK demo_task;
> 
> It's a type in fact. Actually, this is bad style, derived from the
> original RTAI API mess. I think we should establish something like
> rt_task_t etc. on the long-term for the Xenomai native skin, keeping the
> current names only for legacy code (Philippe?).
> 
>> /* NOTE: error handling omitted. */
>>
>> void demo(void *arg)
>> {
>>
>>           RTIME now, previous;
>>
>>     /*
>>      * Arguments: &task (NULL=self),
>>      *            start time,
>>      *            period (here: 1 s)
>>      */
>>     rt_task_set_periodic(NULL, TM_NOW, 1000000000);
>>
>>     previous = rt_timer_read();
>>
>>     while (1) {
>>         rt_task_wait_period(NULL);
>>         now = rt_timer_read();
>>
>>         /*
>>          * NOTE: printf may have unexpected impact on the timing of
>>          *       your program. It is used here in the critical loop
>>          *       only for demonstration purposes.
>>          */
>>         printf("Time since last turn: %ld.%06ld ms\n",
>>                (long)(now - previous) / 1000000,
>>                (long)(now - previous) % 1000000);
>>                previous = now;
>>     }
>> }
>>
>>
>> [The purpose of this function eludes me ?]
>> void catch_signal(int sig)
>> {
>> }
> 
> POSIX signal handling (not Xenomai-related): makes pause() below return
> when some of the caught signals arrive.
> 
>> int main(int argc, char* argv[])
>> {
>>
>> [What is happening here?]
>>     signal(SIGTERM, catch_signal);
>>     signal(SIGINT, catch_signal);
> 
> # man signal
> 
>> [Does this mean I cannot access global variables if this program is
>> running in a thread? That would be a disastrous limitation!]
>>     /* Avoids memory swapping for this program */
>>     mlockall(MCL_CURRENT|MCL_FUTURE);
> 
> ??? There is no such limitation. It's the plain thread programming model
> like with normal pthreads.
> 
> # man mlockall
> 
>>     /*
>>      * Arguments: &task,
>>      *            name,
>>      *            stack size (0=default),
>>      *            priority,
>>      *            mode (FPU, start suspended, ...)
>>      */
>> [I presume this sets the function "demo" as a real-time task?]
>>     rt_task_create(&demo_task, "trivial", 0, 99, 0);
> 
> No, it just creates that task object, the function is set below.
> 
>>     /*
>>      * Arguments: &task,
>>      *            task function,
>>      *            function argument
>>      */
>>     rt_task_start(&demo_task, &demo, NULL);
>> [Is RTASK a task label? What happens if there are more than 1 task to
>> run in separate threads?]
> 
> RT_TASK is the type of a task /descriptor/ (like a file descriptor or
> pthread_t). You can have more tasks by playing with more descriptors.
> 
>> [How is the loop broken to get to this part of the program?]
>>     pause();
> 
> see above
> 
>>     rt_task_delete(&demo_task);
>> }
>>
>>
>> Kindly,
>>
>> Roland.
>>
> 
> HTH,
> Jan
>