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44
Functional Components of ThreadX
Execution Overview
There are four types of program execution within a
ThreadX application: Initialization, Thread Execution,
Interrupt Service Routines (ISRs), and Application
Timers.
Figure 2 on page 45 shows each different type of
program execution. More detailed information about
each of these types is found in subsequent sections
of this chapter.
Initialization
As the name implies, this is the first type of program
execution in a ThreadX application. Initialization
includes all program execution between processor
reset and the entry point of the thread scheduling
loop.
Thread Execution
After initialization is complete, ThreadX enters its
thread scheduling loop. The scheduling loop looks
for an application thread ready for execution. When a
ready thread is found, ThreadX transfers control to it.
After the thread is finished (or another higher-priority
thread becomes ready), execution transfers back to
the thread scheduling loop to find the next highest
priority ready thread.
This process of continually executing and scheduling
threads is the most common type of program
execution in ThreadX applications.
Interrupt Service
Routines (ISR)
Interrupts are the cornerstone of real-time systems.
Without interrupts it would be extremely difficult to
respond to changes in the external world in a timely
manner. On detection of an interrupt, the processor
saves key information about the current program
execution (usually on the stack), then transfers
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