User guide
Neuron C Programmer’s Guide 155
associated periodic system timer interrupt as needed; see
Controlling Interrupts
on page
159.
One application for periodic system timer interrupts could be to provide audio
output for your application. Audio output generally requires a minimum of an 8
kHz signal, and a Series 5000 chip can process interrupts at an 8 kHz rate while
providing full network communication support for the application.
Defining an Interrupt Task
Within your Neuron C application, you can define one interrupt task for each
interrupt source. The interrupt task definition specifies the interrupt source,
interrupt type, and the interrupt condition. An interrupt task looks similar to
the familiar Neuron C when task, but uses the interrupt keyword rather than the
when keyword. However, interrupt tasks are not scheduled by the application
scheduler.
The basic syntax for an interrupt task is:
interrupt (
pin
,
condition
)
interrupt (
object-name
)
interrupt (repeating)
interrupt (repeating,
freq
)
pin
specifies the I/O pin for an I/O interrupt
condition
specifies the interrupt trigger condition for an I/O
interrupt
object-name
specifies the timer/counter I/O object name for a
timer/counter interrupt
repeating defines a periodic system timer interrupt
freq
specifies the frequency for a periodic system timer
interrupt
The following sections describe how to define each type of interrupt task.
Defining an I/O Interrupt Task
An I/O interrupt references an I/O pin, IO_0 .. IO_11. The I/O interrupt can use
the same I/O pin keyword that you use to declare the I/O object, but you do not
need to declare an I/O object for the pin used with an I/O interrupt. The I/O pin
can be an input signal or an output signal.
You can define up to two I/O interrupts, which are dispatched in declaration
order. If you define a third I/O interrupt task, the Neuron C compiler issues
error NCC#577.
You declare the trigger condition for the I/O interrupt through a level indicator,
‘+’ or ‘-‘, or by using the clockedge keyword, as shown in
Table 10 on page 156.