SCHEDULING DESIGN
Built around the next event.
QRT programs the hardware timer for the next scheduled event. Follow the path from timer expiry to application execution.
THE MECHANISM
The next event sets the timer.
Timed wakeups follow scheduled events. Application execution also depends on interrupt handling and the scheduler.
01
Choose the next timed event
Use the next scheduled event to determine when the hardware timer should expire.
02
Process the timer expiry
Handle the event and make any waiting work eligible to run.
03
Dispatch eligible work
The scheduler selects which ready thread runs. Other work and interrupt activity affect when execution begins.
TIMING TERMS
Define the timing.
Then measure it.
Timer resolution
The granularity with which the configured timer can represent time.
Timer clock + configuration
Interrupt response
The interval between the timer event and the start of its interrupt handler.
Timer event → handler entry
Thread response
The interval between the timer event and the waiting thread resuming execution.
Timer event → thread resumes
EVALUATION
Put your workload on the timeline.
Evaluate the complete response path on your target, with the work your application runs.
State the target
Board, CPU clock, timer source, kernel version and build configuration.
01
Show the distribution
Defined endpoints, sample count, percentiles and maximum observed response.
03
Describe the load
Runnable threads, interrupt traffic, priorities and critical sections.
02
Make it reproducible
Test code, measurement method, raw traces and measurement overhead.
04
DESIGN QUESTIONS
The details engineers ask for.
Does timer resolution tell me when my thread will run?
Timer resolution describes the timer's granularity. Interrupt handling, scheduler decisions and competing work also
affect when the thread resumes. Measure those intervals separately.
Does a precise wakeup guarantee a deadline?
A completion deadline also depends on execution time, interference and the application's scheduling assumptions.
Evaluate the full workload against its deadlines.
Is the maximum observed response a worst-case bound?
A test reports the conditions and samples it covers. A worst-case bound needs analysis and explicit assumptions
beyond the maximum observed in a measurement run.
Get Started
Talk to the team
Reach out to the team for licensing, technical questions, or evaluation.
contact@preemptsystems.com
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33500 Tampere
FINLAND