A precise time synchronization method for real-time schedulers

Tatsushi Kikutani, Takahiro Yakoh

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

This paper proposed a precise time synchronization method between schedulers of real-time operating systems by communicating timestamps over a network. An NTP based communication protocol was used to measure the time offset between nodes. To minimize the measurement error, a light-weight network stack called RT-Messenger was used instead of common TCP/IP stack. Also, a Kalman filter was introduced to eliminate such error and to estimate time offset and drift. Furthermore, a real-time scheduler in RTAI/Linux was modified to compensate the time difference using the estimated offset and drift. The time compensation of a scheduler clock affects the next resume times for realtime tasks. Therefore, a re-calculation process of next resume times for all real-time tasks and a re-ordering process of reak-time task queue were added into the real-time scheduler. To validate the proposed method, time differences of resume times for two real-time tasks on different nodes were measured under various experimental conditions. The results confirm that the resume time differences were successfully kept lower than 400 ns with 300 ns standard deviation under the condition of observation period at 1 s and correction period at 10 s.

Original languageEnglish
Pages (from-to)695-702
Number of pages8
JournalIEEJ Transactions on Electronics, Information and Systems
Volume138
Issue number6
DOIs
Publication statusPublished - 2018 Jan 1

Fingerprint

Measurement errors
Kalman filters
Clocks
Synchronization
Network protocols
Linux
Compensation and Redress

Keywords

  • Kalman filter
  • Real-time operating system
  • Time synchronization

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

Cite this

A precise time synchronization method for real-time schedulers. / Kikutani, Tatsushi; Yakoh, Takahiro.

In: IEEJ Transactions on Electronics, Information and Systems, Vol. 138, No. 6, 01.01.2018, p. 695-702.

Research output: Contribution to journalArticle

@article{d1fb26b3bc24417ba01c88dbfaac37b9,
title = "A precise time synchronization method for real-time schedulers",
abstract = "This paper proposed a precise time synchronization method between schedulers of real-time operating systems by communicating timestamps over a network. An NTP based communication protocol was used to measure the time offset between nodes. To minimize the measurement error, a light-weight network stack called RT-Messenger was used instead of common TCP/IP stack. Also, a Kalman filter was introduced to eliminate such error and to estimate time offset and drift. Furthermore, a real-time scheduler in RTAI/Linux was modified to compensate the time difference using the estimated offset and drift. The time compensation of a scheduler clock affects the next resume times for realtime tasks. Therefore, a re-calculation process of next resume times for all real-time tasks and a re-ordering process of reak-time task queue were added into the real-time scheduler. To validate the proposed method, time differences of resume times for two real-time tasks on different nodes were measured under various experimental conditions. The results confirm that the resume time differences were successfully kept lower than 400 ns with 300 ns standard deviation under the condition of observation period at 1 s and correction period at 10 s.",
keywords = "Kalman filter, Real-time operating system, Time synchronization",
author = "Tatsushi Kikutani and Takahiro Yakoh",
year = "2018",
month = "1",
day = "1",
doi = "10.1541/ieejeiss.138.695",
language = "English",
volume = "138",
pages = "695--702",
journal = "IEEJ Transactions on Electronics, Information and Systems",
issn = "0385-4221",
publisher = "The Institute of Electrical Engineers of Japan",
number = "6",

}

TY - JOUR

T1 - A precise time synchronization method for real-time schedulers

AU - Kikutani, Tatsushi

AU - Yakoh, Takahiro

PY - 2018/1/1

Y1 - 2018/1/1

N2 - This paper proposed a precise time synchronization method between schedulers of real-time operating systems by communicating timestamps over a network. An NTP based communication protocol was used to measure the time offset between nodes. To minimize the measurement error, a light-weight network stack called RT-Messenger was used instead of common TCP/IP stack. Also, a Kalman filter was introduced to eliminate such error and to estimate time offset and drift. Furthermore, a real-time scheduler in RTAI/Linux was modified to compensate the time difference using the estimated offset and drift. The time compensation of a scheduler clock affects the next resume times for realtime tasks. Therefore, a re-calculation process of next resume times for all real-time tasks and a re-ordering process of reak-time task queue were added into the real-time scheduler. To validate the proposed method, time differences of resume times for two real-time tasks on different nodes were measured under various experimental conditions. The results confirm that the resume time differences were successfully kept lower than 400 ns with 300 ns standard deviation under the condition of observation period at 1 s and correction period at 10 s.

AB - This paper proposed a precise time synchronization method between schedulers of real-time operating systems by communicating timestamps over a network. An NTP based communication protocol was used to measure the time offset between nodes. To minimize the measurement error, a light-weight network stack called RT-Messenger was used instead of common TCP/IP stack. Also, a Kalman filter was introduced to eliminate such error and to estimate time offset and drift. Furthermore, a real-time scheduler in RTAI/Linux was modified to compensate the time difference using the estimated offset and drift. The time compensation of a scheduler clock affects the next resume times for realtime tasks. Therefore, a re-calculation process of next resume times for all real-time tasks and a re-ordering process of reak-time task queue were added into the real-time scheduler. To validate the proposed method, time differences of resume times for two real-time tasks on different nodes were measured under various experimental conditions. The results confirm that the resume time differences were successfully kept lower than 400 ns with 300 ns standard deviation under the condition of observation period at 1 s and correction period at 10 s.

KW - Kalman filter

KW - Real-time operating system

KW - Time synchronization

UR - http://www.scopus.com/inward/record.url?scp=85048045738&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85048045738&partnerID=8YFLogxK

U2 - 10.1541/ieejeiss.138.695

DO - 10.1541/ieejeiss.138.695

M3 - Article

AN - SCOPUS:85048045738

VL - 138

SP - 695

EP - 702

JO - IEEJ Transactions on Electronics, Information and Systems

JF - IEEJ Transactions on Electronics, Information and Systems

SN - 0385-4221

IS - 6

ER -