SCIOPTA - Real-Time Kernel
User’s Manual Manual Version 4.1 5-7
SCIOPTA - Real-Time Kernel
5 Processes
5.8 Timer Processes
A timer process in SCIOPTA is a specific interrupt process connected to the tick timer of the operating system.
SCIOPTA is calling each timer process periodically derived from the operating system tick counter.
When configuring or creating a timer process, t
he user defines the number of system ticks to expire from one call
to the other individually for each process.
Timer processes will be used for tasks which need to be exe
cuted at precise cyclic intervals. For instance checking
a status bit or byte at well defined moments in time can be performed by timer processes.
Another example is to measure a voltage
at regular intervals. As timer processes execute on the interrupt level of
the timer interrupt it is assured that no voltage measurement samples are lost.
As the timer process runs on interrupt level it is as important as
for normal interrupt processes to return as fast as
possible.
5.8.1 Creating and Declaring Timer Processes
Static timer processes are defined in the SCIOPTA configuration utility (SCONF) and created by the kernel auto-
matically at system startup. See also chapter
16.12 “Creating Processes and Pools” on page 16-18.
Dynamic timer process are
created by using the sc_procTimCreate system call and killed dynamically with the
sc_procKill system call.
5.8.2 Timer Process Priorities
The priority of an interrupt process is assigned by hardware of the interrupt source which is used for the timer proc-
ess. Whenever a timer interrupt o
ccurs the assigned timer interrupt process is called, assuming that no other inter-
rupt of higher priority is running.
5.8.3 Writing Timer Processes
Timer processes are written exactly the same way as interrupt processes. Please consult chapter 5.7.3 “Writing In-
terrupt Processes” on page 5-5 for information how to write interrupt processes.
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