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SCIOPTA - Real-Time Kernel

User’s Manual Manual Version 4.1 5-1

SCIOPTA - Real-Time Kernel

5 Processes

5.1 Introduction

An independent instance of a program running under the control of SCIOPTA is called process. SCIOPTA is as-

signing CPU time by the use of processes and guarantees that

at every instant of time, the most important process

ready to run is executing. The system interrupts processes if other processes with higher priority must execute (be-

come ready).

All SCIOPTA processes have system wide unique process identities.

A SCIOPTA process is always part of a SC

IOPTA module. Please consult chapter 4 “Modules” on page 4-1 for

more information about SCIOPTA modules.

5.2 Process States

A process running under SCIOPTA is always in the RUNNING, READY or WAITING state.

5.2.1 Running

Figure 5-1: State Diagram of SCIOPTA Kernel

RUNNING

READY

WAITING

dispatch

preemption

rx (receive)

tx (transmit)

start process

(higher priority)

tx (transmit)

start process (lower or same priority)

stop process

sleep

If the process is in the running state it ex-

ecutes on the CPU. Only one process can

in running state in a single CPU sys-

tem.

5.2.2 Ready

If a process is in the ready state it is ready

to run meaning the process needs the

CPU, but another process with higher pri-

ority is running.

5.2.3 Waiting

If a process is in the waiting state it is

waiting for events to happen and does not

need the CPU meanwhile. The reasons to

be in the waiting state can be:

• The process tried to receive a mes-

sage which has (not yet) arrived.

• The process called the sleep system

call and wai

ts for the delay to expire.

• The process waits on a SCIOPTA

tri

gger.

• The Process waits on a start system

call

if it was previously stopped.

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