CompuLab SBC-X270 Manual de usuario descargar pdf (Pagina 54)

SCIOPTA - Real-Time Kernel

5-14 Manual Version 4.1 User’s Manual

SCIOPTA - Real-Time Kernel

5 Processes

5.14 Process Variables

Each process can store local variables inside a protected data area. Process variables are variables which can only

be accesses by functions within the context of the process.

The process variable are usually maintained inside a SCIO

PTA message and managed by the kernel. The user can

access the process variable by specific system calls.

Figure 5-6: SCIOPTA Process Variables

Process Control Block

Process Variable Message

PCB

Message ID

Reserved by the kernel

TAG 1

Variable 1

TAG 2

TAG 3

TAG 4

TAG n

Variable 2

Variable 3

Variable 4

Variable n

Process Variables

Pointer

There can be one process variable data area per process. The user needs to allocate a message to hold the process

variables. Each variable is preceded by a user defined tag which is used to access the variable. The tag and the proc-

ess variable have a fixed size large enough to hold a pointer.

It is the user´s responsibility to allocate a big enough message buffer to hold the maximum needed number of proc-

ess variables. The message buffer holdi

ng the variable array will be removed from the process. The process may

no longer access this buffer directly. But it can retrieve the buffer if for instance the number of variables must be

changed.

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 225 226

CompuLab SBC-X270 Manual de usuario Pagina 54