realtime.c

// Copyright (c) 2014 Adafruit Industries
// Author: Tony DiCola

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#include <errno.h>
#include <sched.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>

#include "realtime.h"

void busy_wait_milliseconds(uint32_t millis) {
  // Set delay time period.
  struct timeval deltatime;
  deltatime.tv_sec = millis / 1000;
  deltatime.tv_usec = (millis % 1000) * 1000;
  struct timeval walltime;
  // Get current time and add delay to find end time.
  gettimeofday(&walltime, NULL);
  struct timeval endtime;
  timeradd(&walltime, &deltatime, &endtime);
  // Tight loop to waste time (and CPU) until enough time as elapsed.
  while (timercmp(&walltime, &endtime, <)) {
    gettimeofday(&walltime, NULL);
  }
}

void sleep_milliseconds(uint32_t millis) {
  struct timespec sleep;
  sleep.tv_sec = millis / 1000;
  sleep.tv_nsec = (millis % 1000) * 1000000L;
  while (clock_nanosleep(CLOCK_MONOTONIC, 0, &sleep, &sleep) && errno == EINTR);
}

void set_max_priority(void) {
  struct sched_param sched;
  memset(&sched, 0, sizeof(sched));
  // Use FIFO scheduler with highest priority for the lowest chance of the kernel context switching.
  sched.sched_priority = sched_get_priority_max(SCHED_FIFO);
  sched_setscheduler(0, SCHED_FIFO, &sched);
}

void set_default_priority(void) {
  struct sched_param sched;
  memset(&sched, 0, sizeof(sched));
  // Go back to default scheduler with default 0 priority.
  sched.sched_priority = 0;
  sched_setscheduler(0, SCHED_OTHER, &sched);
}