RT test applicatioin for BeagleBone Black.

test_port_rt.c

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <sched.h>
#include <sys/mman.h>
#include <string.h>
#include <unistd.h>

#define MY_PRIORITY (49) /* we use 49 as the PRREMPT_RT use 50
                            as the priority of kernel tasklets
                            and interrupt handler by default */

#define MAX_SAFE_STACK (8*1024) /* The maximum stack size which is
                                   guaranteed safe to access without
                                   faulting */

#define NSEC_PER_SEC (1000000000) /* The number of nsecs per sec. */

void stack_prefault(void) {
  unsigned char dummy[MAX_SAFE_STACK];
	memset(dummy, 0, MAX_SAFE_STACK);
	return;
}

int main(int argc, char* argv[])
{
	FILE *PortHandle = NULL;
	char *LEDBrightness = "/sys/class/leds/beaglebone:green:usr3/brightness";
	
	struct timespec t;
	struct sched_param param;
	int i, interval = 1000000; /* 1ms*/
	
	/* Initialize for GPIO */
	if((PortHandle = fopen("/sys/class/gpio/export", "ab")) == NULL){
		printf("Unable to register gpio port.\n");
		return 1;
	}
	fwrite("60", sizeof(char), 2, PortHandle);
	fclose(PortHandle);
	
	if((PortHandle = fopen("/sys/class/gpio/gpio60/direction", "rb+")) == NULL){
		printf("Unable to register gpio direction.\n");
		return 1;
	}
	fwrite("out", sizeof(char), 3, PortHandle);
	fclose(PortHandle);
	
	/* Declare ourself as a real time task */
	param.sched_priority = MY_PRIORITY;
	if(sched_setscheduler(0, SCHED_FIFO, &param) == -1) {
		perror("sched_setscheduler failed");
		exit(-1);
	}
	
	/* Lock memory */
	if(mlockall(MCL_CURRENT|MCL_FUTURE) == -1) {
		perror("mlockall failed");
		exit(-2);
	}
	
	/* Pre-fault our stack */
	stack_prefault();
	
	clock_gettime(CLOCK_MONOTONIC ,&t);
	/* start after one second */
	t.tv_sec++;
	
	for(i=0;i<120000;i++) {
		/* wait until next shot */
		clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &t, NULL);
		
		/* do the stuff */
		if((PortHandle = fopen("/sys/class/gpio/gpio60/value", "rb+")) == NULL){
			printf("Unable to write gpio value.\n");
			return 1;
		}
		if(i%20 == 0){
			fwrite("1", sizeof(char), 1, PortHandle);
		}else{
			fwrite("0", sizeof(char), 1, PortHandle);
		}
		fclose(PortHandle);
		
		/* calculate next shot */
		t.tv_nsec += interval;
		
		while (t.tv_nsec >= NSEC_PER_SEC) {
			t.tv_nsec -= NSEC_PER_SEC;
			t.tv_sec++;
		}
	}
	
	/* Deiitialize for GPIO */
	if((PortHandle = fopen("/sys/class/gpio/unexport", "ab")) == NULL){
		printf("Unable to unregister gpio port.\n");
		return 1;
	}
	fwrite("60", sizeof(char), 2, PortHandle);
	fclose(PortHandle);

	return 0;
}