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QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
Programming
Getting Started with QNX Neutrino
Getting Started with QNX Neutrino: A Guide for Realtime Programmers is intended to introduce you to the QNX Neutrino RTOS and help you develop applications and resource managers for it.
Clocks, Timers, and Getting a Kick Every So Often
It's time to take a look at everything related to time in the QNX Neutrino RTOS. We'll see how and why you'd use timers and the theory behind them. Then we'll take a look at getting and setting the realtime clock.
Clocks and timers
Let's look at a typical system, say a car. In this car, we have a bunch of programs, most of which are running at different priorities. Some of these need to respond to actual external events (like the brakes or the radio tuner), while others need to operate periodically (such as the diagnostics system). In this section, we'll explain how clocks and timers can help us achieve this.
Base timing resolution
Let's say that the timer tick is operating at just slightly faster than 10 ms. Can I reliably sleep for 3 milliseconds?

QNX Momentics IDE User's Guide
This User's Guide describes version 7.1 of the Integrated Development Environment (IDE) that's part of the QNX Momentics tool suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
- Quickstart Guide
- OS Components & Operations
- Audio & Graphics API
- Multimedia
- Networking Middleware
- Programming
  - Getting Started with QNX Neutrino
    Getting Started with QNX Neutrino: A Guide for Realtime Programmers is intended to introduce you to the QNX Neutrino RTOS and help you develop applications and resource managers for it.
    - Processes and Threads
    - Message Passing
      In this chapter, we'll look at the most distinctive feature of QNX Neutrino, message passing. Message passing lies at the heart of the operating system's microkernel architecture, giving the OS its modularity.
    - Clocks, Timers, and Getting a Kick Every So Often
      It's time to take a look at everything related to time in the QNX Neutrino RTOS. We'll see how and why you'd use timers and the theory behind them. Then we'll take a look at getting and setting the realtime clock.
      - Clocks and timers
        Let's look at a typical system, say a car. In this car, we have a bunch of programs, most of which are running at different priorities. Some of these need to respond to actual external events (like the brakes or the radio tuner), while others need to operate periodically (such as the diagnostics system). In this section, we'll explain how clocks and timers can help us achieve this.
        Operating periodically
        So how does the diagnostics system operate periodically?
        Clock interrupt sources
        So where does the clock interrupt come from?
        Base timing resolution
        Let's say that the timer tick is operating at just slightly faster than 10 ms. Can I reliably sleep for 3 milliseconds?
        Timing jitter
        There's one more thing you have to worry about. Let's say the timing resolution is 10 ms and you want a 20 ms timeout.
        Types of timers
        The type of timer shown above is a relative timer. The timeout period selected is relative to the current time. If you want the timer to delay your thread until a precise moment in the future, you have to calculate the number of seconds from now until then, and set up a relative timer for that number of seconds. Because this is a fairly common function, QNX Neutrino implements an absolute timer that will delay until the specified time (instead of for the specified time, like a relative timer).
        Notification schemes
        How do you receive a timeout notification? With the delay timer, you received notification by virtue of being made READY again.
      - Using timers
        Having looked at all this wonderful theory, let's turn our attention to some specific code samples to see what you can do with timers.
      - Advanced topics
        Now that we've seen the basics of timers, we'll look at a few advanced topics.
    - Interrupts
      In this chapter, we'll take a look at interrupts, how we deal with them under QNX Neutrino, their impact on scheduling and realtime, and some interrupt-management strategies.
    - Resource Managers
      In this chapter, we'll take a look at what you need to understand in order to write a resource manager. Resource managers are another distintive feature of QNX Neutrino that allow you to access services through standard POSIX calls.
    - Sample Programs
      This appendix contains the complete versions of some of the sample programs discussed in this book.
    - Glossary
  - Programmer's Guide
    The QNX Neutrino Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX Neutrino RTOS.
  - The QNX Neutrino Cookbook: Recipes for Programmers
  - Writing a Resource Manager
- Sensor Framework
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX Neutrino RTOS system and developers who want to create a QNX Neutrino resource manager free from vulnerabilities.
- Utilities & Libraries
QNX Hypervisor
The QNX Hypervisor allows you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX software in Amazon Web Services (AWS) and Microsoft Azure (Azure).
QNX Advanced Virtualization Frameworks User's Guide
This User's Guide is aimed at all systems integrators and developers who want to design and build embedded systems using the QNX Advanced Virtualization Frameworks.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation and explains how to obtain technical support.

Base timing resolution

Let's say that the timer tick is operating at just slightly faster than 10 ms. Can I reliably sleep for 3 milliseconds?

Nope (or at least, not originally).

Consider what happens in the kernel. You issue the C Library delay() call to go to sleep for 3 milliseconds. The kernel has to set the variable in the ISR to some value. If it sets it to the current time, this means the timer has already expired and that you should wake up immediately. If it sets it to one tick more than the current time, this means that you should wake up on the next tick (up to 10 milliseconds away).

The moral of this story is: Don't expect timing resolution any better than the input timer tick rate.

This has changed; in QNX Neutrino 7.0 and later, you can use a high-resolution timer. For details, see Tolerant and high-resolution timers in the Understanding the Microkernel's Concept of Time chapter of the Programmer's Guide.

Getting more precision

Under QNX Neutrino, a program can adjust the value of the hardware divisor component in conjunction with the kernel (so that the kernel knows what rate the timer tick ISR is being called at). We'll look at this below in the Getting and setting the realtime clock section.

Page updated: March 12, 2026