INtime® 3.1 Software - tenAsys

Chapter 4: About RT programming
when you need to respond to a new interrupt. Interrupt processing is also more
efficient, since your system spends all of its time running threads, not polling for
interrupts.
Determinism
INtime software provides deterministic response by establishing a predictable,
worst-case response time to a high-priority interrupt. Deterministic response time
includes these components:
• Interrupt response time: The time that elapses between a physical interrupt and
the start of interrupt handler execution. A predictable worst-case response time to
interrupt processing ensures that incoming data is handled before it becomes invalid.
• Thread switch time: The time that elapses between exiting one thread and starting
another. To exit a thread, the RT kernel must save data registers, stack and
execution pointers (the thread state) of one thread. Minimized thread switch time
also provides a predictable response time to a high-priority thread.
Since the typical response to an interrupt includes invoking a handler and then
performing a thread switch to an interrupt thread, the deterministic response time
includes both the interrupt response and thread switch times.
RT response does not mean instantaneous execution. A high-priority thread that is
very long and performs many calculations uses as much processor time to execute on
an RT system as on any other system. The length of time instructions take to execute is
a function of processor speed.
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