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Init jitter, mean and variance calc for NTP vs GPS ts

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Umar Farooq 2017-04-26 16:16:15 +00:00
parent a7a621ebe5
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/** Calc jitter, mean and variance of GPS vs NTP TS.
*
* @author Umar Farooq <umar.farooq@rwth-aachen.de>
* @copyright 2017, Institute for Automation of Complex Power Systems, EONERC
*********************************************************************************/
/** @addtogroup hooks Hook functions
* @{
*/
#include "hook.h"
#include "plugin.h"
#include "timing.h"
#define CALC_GPS_NTP_DELAY 0 /* @todo move to global config file */
#define GPS_NTP_DELAY_WIN_SIZE 16
static int64_t jitter_val[GPS_NTP_DELAY_WIN_SIZE] = {0};
static int64_t delay_series[GPS_NTP_DELAY_WIN_SIZE] = {0};
static int64_t moving_avg[GPS_NTP_DELAY_WIN_SIZE] = {0};
static int64_t moving_var[GPS_NTP_DELAY_WIN_SIZE] = {0};
static int64_t delay_mov_sum = 0, delay_mov_sum_sqrd = 0;
static int curr_count = 0;
/**
* Hook to calculate jitter between GTNET-SKT GPS timestamp and Villas node NTP timestamp.
*
* Drawbacks: No protection for out of order packets. Default positive delay assumed,
* so GPS timestamp should be earlier than NTP timestamp. If difference b/w NTP and GPS ts
* is high (i.e. several mins depending on GPS_NTP_DELAY_WIN_SIZE),
* the variance value will overrun the 64bit value.
*/
int hook_jitter_ts(struct hook *h, struct sample *smps[], size_t *cnt)
{
/* @todo save data for each node, not just displaying on the screen, doesn't work for more than one node!!! */
struct timespec now = time_now();
int64_t delay_sec, delay_nsec, curr_delay_us;
for(int i = 0; i < *cnt; i++) {
delay_sec = now.tv_sec - smps[i]->ts.origin.tv_sec;
delay_nsec = now.tv_nsec - smps[i]->ts.origin.tv_nsec;
/* Calc on microsec instead of nenosec delay as variance formula overflows otherwise.*/
curr_delay_us = delay_sec*1000000 + delay_nsec/1000;
delay_mov_sum = delay_mov_sum + curr_delay_us - delay_series[curr_count];
moving_avg[curr_count] = delay_mov_sum/(GPS_NTP_DELAY_WIN_SIZE); /* Will be valid after GPS_NTP_DELAY_WIN_SIZE initial values */
delay_mov_sum_sqrd = delay_mov_sum_sqrd + (curr_delay_us*curr_delay_us) - (delay_series[curr_count]*delay_series[curr_count]);
moving_var[curr_count] = (delay_mov_sum_sqrd - (delay_mov_sum*delay_mov_sum)/GPS_NTP_DELAY_WIN_SIZE)/(GPS_NTP_DELAY_WIN_SIZE-1);
delay_series[curr_count] = curr_delay_us; /* Update the last delay value */
/* Jitter calc formula as used in Wireshark according to RFC3550 (RTP)
D(i,j) = (Rj-Ri)-(Sj-Si) = (Rj-Sj)-(Ri-Si)
J(i) = J(i-1)+(|D(i-1,i)|-J(i-1))/16
*/
jitter_val[(curr_count+1)%GPS_NTP_DELAY_WIN_SIZE] = jitter_val[curr_count] + (abs(curr_delay_us) - jitter_val[curr_count])/16;
info("jitter %ld usec, moving average %ld usec, moving variance %ld usec\n", jitter_val[(curr_count+1)%GPS_NTP_DELAY_WIN_SIZE], moving_avg[curr_count], moving_var[curr_count]);
curr_count++;
if(curr_count >= GPS_NTP_DELAY_WIN_SIZE)
curr_count = 0;
}
return 0;
}
#if CALC_GPS_NTP_DELAY == 1
static struct plugin p = {
.name = "jitter_calc",
.description = "Calc jitter, mean and variance of GPS vs NTP TS",
.type = PLUGIN_TYPE_HOOK,
.hook = {
.priority = 0,
.builtin = true,
.read = hook_jitter_ts,
}
};
REGISTER_PLUGIN(&p)
#endif
/** @} */