SCIOPTA - Real-Time Kernel
User’s Manual Manual Version 4.1 5-3
SCIOPTA - Real-Time Kernel
5 Processes
5.5 Process Identity
Each process has a unique process identity (process ID) which is used in SCIOPTA system calls when processes
need to be addressed.
The process ID will be allocated by the operating system for all processes which you have entered during
SCIOPTA
configuration (static processes) or will be returned when you are creating processes dynamically. The
kernel maintains a list with all process names and their process IDs.
The user can get Process IDs by using a sc_procIdGet
system call including the process name.
5.6 Prioritized Processes
In SCIOPTA a process can be seen as an independent program which executes as if it has the whole CPU available.
The operating systems guarantees that always the most important process at a certain moment is executing. In a
typical SCIOPTA system prioritized processes are the most common used process types. Each prioritized process
has a priority and the SCIOPTA scheduler is running ready processes according to these priorities. The process
with higher priority runs (gets the CPU) before the process with lower priority.
If a process has terminated its job for the moment by for example waiting on a message which has not yet been sent
o
r by calling the kernel sleep function, the process is put into the waiting state and is not any longer ready.
Most of the time in a SCIOPTA real-time sys
tem is spent in prioritized processes. It is where collected data is an-
alysed and complicated control
structures are executed.
Prioritized processes respond much slower than
interrupt processes, but they can spend a relatively long time to
work with data.
5.6.1 Creating and Declaring Prioritized Processes
Static prioritized processes are defined in the SCIOPTA configuration utility (SCONF) and created by the kernel
automatically at system startup. See also chapter
16.12 “Creating Processes and Pools” on page 16-18.
Dynamic prioritized process are
created by using the sc_prioProcCreate system call and killed dynamically with
the sc_procKill system call.
5.6.2 Process Priorities
Each SCIOPTA process has a specific priority. The user defines the priorities at system configuration or when cre-
ating the process. Process prioriti
es can be modified during run-time.
By assigning a priority the user designs groups of processes or parts of systems according to respons
e time require-
ments. Ready processes with high priority
are always interrupting processes with lower priority. Subsystems with
high priority processes have therefore faster response time. Priority values for prioritized processes in SCIOPTA
can be from 0 to 31. 0 is the highest and 31 the lowest priority level.
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