Echelon Neuron C - Manual (Page 29)

Neuron C Programmer’s Guide 17
In this example above, when the led_timer application timer (definition not
shown in this example) expires, the body of code (the task) that follows the when
clause is executed to turn off the specified I/O object, io_led (also defined
elsewhere in the program). After this task has been executed, the timer_expires
event is automatically cleared. Its task is then ignored until the LED timer
expires again and the when clause again evaluates to TRUE.
The following examples demonstrate various ways of using tasks and events.
More information about tasks and events can be found in Chapter 7,
Additional
Features , on page 145, and Figure 14 on page 147.
when (reset)
when (io_changes(io_switch))
when (!timer_expires)
when (flush_completes && (y == 5))
when (x == 3)
{
// Turn on the LED and start the timer
. . .
}
The when clauses cannot be nested. For example, the following nested when
clause is not valid:
when (io_changes(io_switch))
{
when (x == 3) { // Can't nest!
...
}
}
An equivalent result may be achieved by testing the event with an if statement:
when (io_changes(io_switch))
{
if (x == 3) {
...
}
}
When Statement
The syntax for a when statement (the when clause or clauses plus the associated
task) is:
when-clause
[when-clause ... ]
task
The syntax for when-clause is:
[priority] [preempt_safe] when ( event )
priority Forces evaluation of the following when clause each time the
scheduler runs. See Priority When Clauses on page 23.
preempt_safe Allows the scheduler to execute the associated when task
even if the application is in preemption mode. See the discussions on
preemption mode in Chapter 6, How Devices Communicate Using
Application Messages , on page 117.