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This illustrates the fundamental idea/schema to write a real-time periodic task in ChronOS.

You will learn how to write a real-time task (locking the memory, i.e. do not allow the OS to swap the application memory) pin a task to a cpu (affinity mask).. all within ChronOS?!

* Antonio Barbalace
* periodic segments benchmark
* this work was done in the integration phase of the AUV code with ChronOS
* The whole code derive from the sched_test_app (Aaron version)
* This version is terrible system with just one periodic thread

#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>
#include "libchronos/chronos.h"

#define SET_SCHED_FLAG        0
#define SET_SCHED_PROC        0

#define UTIL                50
#define PERIOD              1000000
#define EXEC                50 

#define JOBS_NUM            32
#define ITER_NUM            4096

/* macros to set or zero cpus in a cpu mask */
#define MASK_ZERO(mask) (mask) = 0
#define MASK_SET(mask, cpu) (mask) |= (unsigned long) pow(2, cpu)

/* TASK_xxx_PRIO */
#define MAIN_PRIO                       98
#define TASK_CREATE_PRIO                96
#define TASK_START_PRIO                 94
#define TASK_CLEANUP_PRIO               92
#define TASK_RUN_PRIO                   90 

/* Numerical definitions */
#define THOUSAND   1000
#define MILLION    1000000
#define BILLION    1000000000 

static pthread_attr_t attr;
static struct sched_param tparam;

static inline long long timespec_subtract_us(struct timespec *x,
                         struct timespec *y)
   long long sec, nsec;
   sec = x->tv_sec - y->tv_sec;
   nsec = x->tv_nsec - y->tv_nsec;
   if (nsec < 0) {
       nsec += BILLION;

   return (sec * MILLION) + (nsec / THOUSAND);
static void find_job_deadline(int job, long period, struct timespec * start_time, struct timespec *deadline)
   unsigned long long nsec, carry;
   unsigned long offset = (job + 1) * period;    //the offset from the start time this deadline is

   nsec = start_time->tv_nsec + offset * THOUSAND;
   carry = nsec / BILLION;

   deadline->tv_nsec = nsec % BILLION;
   deadline->tv_sec = start_time->tv_sec + carry;
void *start_task(void *arg)
   int job;
   long period = PERIOD;
   long i, l;
   struct sched_param param;
   struct timespec start_time, end_time, deadline, release, tperiod;

   tperiod.tv_sec = PERIOD / MILLION;
   tperiod.tv_nsec = (PERIOD % MILLION) * THOUSAND;

   pid_t tid, pid;
   long long tardiness;
   unsigned long thread_mask = SET_SCHED_PROC;

   //set the affinity of this thread to whatever was specified in the taskset file
   if(sched_setaffinity(0, sizeof(thread_mask), (cpu_set_t *) &thread_mask)) {
       printf("Failed to set processor affinity of a task.");

   //increase priority to TASK_START_PRIO
   param.sched_priority = TASK_START_PRIO;
   pthread_setschedparam(pthread_self(), SCHED_FIFO, &param);

   //get the start time and CAS on the start-time so all the threads agree on when they got here
   clock_gettime(CLOCK_REALTIME, &start_time);

   // periodic LOOP
   for (job = 0; job < JOBS_NUM; job++) {
       find_job_deadline(job, period, &start_time, &deadline);    //find the deadline for this taskset
       clock_gettime(CLOCK_REALTIME, &release);    // real release time

       //enter real-time segment
       begin_rtseg_self(TASK_RUN_PRIO, UTIL, &deadline, &tperiod, EXEC);

       // DO SOMETHING like a printf... :-)
       printf("job %d\n", job);
       l = 123456789;
       for (i = 0; i < ITER_NUM; i++) {
           l *= i;
           // or nop
       i = l;

       //end real time segment
       clock_gettime(CLOCK_REALTIME, &end_time);    //get the endtime
       end_rtseg_self(TASK_CLEANUP_PRIO);    //end the real-time segment

       tardiness = timespec_subtract_us(&deadline, &end_time);    //calculate tardiness from deadline and endtime

       if (tardiness >= 0) {    //otherwise, did we meet our deadline?
           //sleep for however much time remains before the next release of this task
           if (tardiness > 0)


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

   int i;
   struct sched_param param, old_param;
   unsigned long main_mask = 0;
   pthread_t thread;

   //TODO we have to put mem lock all and mem unlock all at the end

   //set outselves as a real-time task
   sched_getparam(0, &old_param);
   param.sched_priority = MAIN_PRIO;
   if (sched_setscheduler(0, SCHED_FIFO, &param) == -1) {
       printf("sched_setscheduler() failed.");
       return 0;

   //set task affinity of this main thread to the first processor
   MASK_SET(main_mask, 0);
   if (sched_setaffinity(0, sizeof(main_mask), (cpu_set_t *) & main_mask) < 0) {
       printf("sched_setaffinity() failed.");
       return 0;

           printf("Selection of RT scheduler failed! Is the scheduler loaded?");
           return 0;

   tparam.sched_priority = TASK_CREATE_PRIO;
   pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
   pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
   pthread_attr_setschedparam(&attr, &tparam);

   if (pthread_create(thread, &attr, start_task,0)) {
           printf("Failed to pthread_create one of the task threads.");
           return 0;
   if (pthread_join(thread, NULL)) {
       printf("Failed to pthread_join one of the task threads.");
       return 0;

   //return us to a normal scheduler and priority
   sched_setscheduler(0, SCHED_OTHER, &old_param);
   return 0;

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