ST20-C1 datasheet(194/205 Pages) STMICROELECTRONICS

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bits are global and are preserved when a process is descheduled and others are

local to a

process and are lost when the process is descheduled.

Task

process.

Task descriptor

The identifier of a

process, which is a pointer to the process descriptor block.

When a process is executing, the Tdesc holds the task descriptor of the process.

Tdesc

A 32-bit register which holds the

task descriptor of the current process.

Thread

A dynamically generated

process.

Timeslice

Deschedule a process to allow other processes access to the CPU. Timeslicing

prevents any one process from occupying too much CPU time. A timesliced

process is normally added to the back of the

scheduling queue and the process on

the front of the queue is restarted.

Trap

exception caused by software, or an interrupt initiating a scheduling event.

Trap handler

The code and data which define what happens when a

trap is taken.

Trapped

A process is trapped when it is waiting for a

trap handler to complete.

Unsigned value

Value which could only be positive, so the most significant bit is not used as a

sign

bit.

Vector

array.

Waiting

A process is waiting for an event if it cannot continue execution until that event has

occurred. The event could be for example a communication or a

semaphore

signal.

Word

A word is a four byte (32-bit) location for data.

Word-aligned

address is word-aligned if it is divisible by 4, i.e. if the least significant two bits

are zero.

Work space

Space in memory for

local variables and values.

ST20-C1 Datasheet(PDF) 194 Page - STMicroelectronics

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