Your browser does not support JavaScript! Skip to main content
Free 30-day trial DO-178C Handbook RapiCoupling Preview DO-178C Multicore Training Multicore Resources
Rapita Systems
 

Industry leading verification tools & services

Rapita Verification Suite (RVS)

  RapiTest - Unit/system testing  RapiCover - Structural coverage analysis  RapiTime - Timing analysis (inc. WCET)  RapiTask - Scheduling visualization  RapiCoverZero - Zero footprint coverage analysis  RapiTimeZero - Zero footprint timing analysis  RapiTaskZero - Zero footprint scheduling analysis  RapiCouplingPreview - DCCC analysis

Multicore Verification

  MACH178  MACH178 Foundations  Multicore Timing Solution  RapiDaemons

Engineering Services

  V&V Services  Data Coupling & Control Coupling  Object code verification  Qualification  Training  Consultancy  Tool Integration  Support

Industries

  Civil Aviation (DO-178C)   Automotive (ISO 26262)   Military & Defense   Space

Other

RTBx Mx-Suite Software licensing Product life cycle policy RVS Assurance issue policy RVS development roadmap

Latest from Rapita HQ

Latest news

SAIF Autonomy to use RVS to verify their groundbreaking AI platform
RVS 3.22 Launched
Hybrid electric pioneers, Ascendance, join Rapita Systems Trailblazer Partnership Program
Magline joins Rapita Trailblazer Partnership Program to support DO-178 Certification
View News

Latest from the Rapita blog

How to certify multicore processors - what is everyone asking?
Data Coupling Basics in DO-178C
Control Coupling Basics in DO-178C
Components in Data Coupling and Control Coupling
View Blog

Latest discovery pages

control_tower DO-278A Guidance: Introduction to RTCA DO-278 approval
Picture of a car ISO 26262
DCCC Image Data Coupling & Control Coupling
Additional Coe verification thumb Verifying additional code for DO-178C
View Discovery pages

Upcoming events

Avionics and Testing Innovations 2025
2025-05-20
DASC 2025
2025-09-14
DO-178C Multicore In-person Training (Fort Worth, TX)
2025-10-01
DO-178C Multicore In-person Training (Toulouse)
2025-11-04
View Events

Technical resources for industry professionals

Latest White papers

Mitigation of interference in multicore processors for A(M)C 20-193
Sysgo WP
Developing DO-178C and ED-12C-certifiable multicore software
DO178C Handbook
Efficient Verification Through the DO-178C Life Cycle
View White papers

Latest Videos

Rapita Systems - Safety Through Quality
Simulation for the Motorola 68020 microprocessor with Sim68020
AI-driven Requirements Traceability for Faster Testing and Certification
Multicore software verification with RVS 3.22
View Videos

Latest Case studies

GMV case study front cover
GMV verify ISO26262 automotive software with RVS
Kappa: Verifying Airborne Video Systems for Air-to-Air Refueling using RVS
Supporting DanLaw with unit testing and code coverage analysis for automotive software
View Case studies

Other Resources

 Webinars

 Brochures

 Product briefs

 Technical notes

 Research projects

 Multicore resources

Discover Rapita

Who we are

The company menu

  • About us
  • Customers
  • Distributors
  • Locations
  • Partners
  • Research projects
  • Contact us

US office

+1 248-957-9801
info@rapitasystems.com
Rapita Systems, Inc.
41131 Vincenti Ct.
Novi
MI 48375
USA

UK office

+44 (0)1904 413945
info@rapitasystems.com
Rapita Systems Ltd.
Atlas House
Osbaldwick Link Road
York, YO10 3JB
UK

Spain office

+34 93 351 02 05
info@rapitasystems.com
Rapita Systems S.L.
Parc UPC, Edificio K2M
c/ Jordi Girona, 1-3
Barcelona 08034
Spain

Working at Rapita

Careers

Careers menu

  • Current opportunities & application process
  • Working at Rapita
Back to Top Contact Us

Safety, WCET and measurements

Breadcrumb

  1. Home
Ian Broster
2012-02-17

I was at a meeting this week where someone put a slide on the screen that contained the sentence "Measuring WCET is unsafe." This statement is wrong on so many counts, and yet seems to be circulating in literature, is widely quoted, and is frequently re-stated "blindly", with no understanding of what it means. As it keeps getting quoted, I thought I'd write something about it.

What's wrong?

Grammar

The first problem that I have with this statement is the grammatical stupidity of this sentence. I've measured WCET many times and I've never hurt myself doing it! However, let's see past that. Let us assume that the implication is that use of a measured WCET is somehow unsafe.

Safety

The study and terminology of "safety" are well defined and well understood. The implication that the use of a measured value leads directly to the (un)safety of a system shows an appalling lack of understanding of the technology.

I doubt that the original user of this sentence (whoever that was!) meant the word "unsafe" to have any connection with "safety". However, the main area where WCET has any use is safety-related, or high reliability computer systems. In this area, which frequently deals with (real) safety issues, we should be very careful to avoid mixing terminology.

When this sentence is quoted, I see that the people reading it do believe that the sentence is related to "safety". Indeed, this wild dramatization is at the heart of why it is quoted so often.

Optimism and Pessimism

Despite the misleading use of the word "unsafe" from a related domain, of course what is meant by "unsafe" is that “a simple measured maximum value may be lower than the true worst case”. It uses the word unsafe in the sense that you might cut a piece of wood slightly larger than you need to “err on the safe side”, then plane it down.

This statement is so obvious that it's almost not worth stating! Of course if you measure something that is changing, your biggest measurement might be smaller than the biggest possible measurement. This is the reason why RapiTime exists in the first place - to automate and supplement your measurements with analysis to make sure that your measurements can be relied upon.

If the sentence was not dressed up in misleading dramatics, then it would not be so widely quoted! It is the over-dramatisation of the use of “unsafe” that makes people quote it blindly.

So please! Let's:

a) stop using terminology from the safety domain out of context to dramatize (we might use optimism and pessimism, or under-estimate and over-estimate as almost equivalent terms)

and

b) actually work out what we mean by measurement of WCET. And that's the subject of a follow-up blog post.

DO-178C webinars

DO178C webinars

White papers

Mitigation of interference in multicore processors for A(M)C 20-193
Sysgo WP Developing DO-178C and ED-12C-certifiable multicore software
DO178C Handbook Efficient Verification Through the DO-178C Life Cycle
A Commercial Solution for Safety-Critical Multicore Timing Analysis

Related blog posts

Why Static analysis doesn't work for Multicore WCET estimation

.
2019-10-07

WCET analysis of object code with zero instrumentation

.
2017-02-27

A funny thing happened on the way to a Worst-Case Execution Time Conference...

.
2015-10-09

Things that make real-time hard - parallelization

.
2013-09-04

Pagination

  • Current page 1
  • Page 2
  • Page 3
  • Page 4
  • Page 5
  • Page 6
  • Next page Next ›
  • Last page Last »
  • Solutions
    • Rapita Verification Suite
    • RapiTest
    • RapiCover
    • RapiTime
    • RapiTask
    • MACH178

    • Verification and Validation Services
    • Qualification
    • Training
    • Integration
  • Latest
  • Latest menu

    • News
    • Blog
    • Events
    • Videos
  • Downloads
  • Downloads menu

    • Brochures
    • Webinars
    • White Papers
    • Case Studies
    • Product briefs
    • Technical notes
    • Software licensing
  • Company
  • Company menu

    • About Rapita
    • Careers
    • Customers
    • Distributors
    • Industries
    • Locations
    • Partners
    • Research projects
    • Contact
  • Discover
    • Multicore Timing Analysis
    • Embedded Software Testing Tools
    • Worst Case Execution Time
    • WCET Tools
    • Code coverage for Ada, C & C++
    • MC/DC Coverage
    • Verifying additional code for DO-178C
    • Timing analysis (WCET) & Code coverage for MATLAB® Simulink®
    • Data Coupling & Control Coupling
    • Aerospace Software Testing
    • Automotive Software Testing
    • Certifying eVTOL
    • DO-178C
    • AC 20-193 and AMC 20-193
    • ISO 26262
    • What is CAST-32A?

All materials © Rapita Systems Ltd. 2025 - All rights reserved | Privacy information | Trademark notice Subscribe to our newsletter