import subprocess
import time
import matplotlib.pyplot as plt

ITERATIONS = 300
ITERATION_DURATION = 1 #second(s)

def set_rt_priority():
   subprocess.run(["schedtool", "-F", "-p", "99"], check=True)

def rt_task():
    new_time = time.time()
    jitter_record = []

    for i in range(ITERATIONS + 1):
        old_time = new_time
        new_time = time.time()

        print("--------------------------------------------------")
        print(f"system time:\t{new_time} s")
        print(f"time diff:\t{new_time - old_time} s")

        # jitter
        jitter = new_time - old_time - ITERATION_DURATION
        jitter_record.append(jitter)
        print(f"jitter:\t{jitter} s")

        # sleep for the rest of one second
        time.sleep(new_time + ITERATION_DURATION - time.time())

    #remove the first measurement
    jitter_record.pop(0) 

    #plot and store the jitter record
    plt.plot(jitter_record)
    plt.title(f"Jitter at {ITERATION_DURATION} s interval")
    plt.xlabel("Iteration")
    plt.ylabel("Jitter (in s)")
    plt.savefig("out.svg")


if __name__ == "__main__":
    set_rt_priority()
    rt_task()