ST20-C1 datasheet(193/205 Pages) STMICROELECTRONICS

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Scheduling kernel

Code to override the ST20 built-in

microcode scheduler, consisting mainly of trap

handlers which are taken when a scheduling event occurs.

Scheduling queue

The

queue of processes waiting for CPU time.

Secondary instruction

An instruction encoded using an

operate instruction component. A secondary

instruction has no data part associated with it, as the instruction data value is used

to identify the instruction.

cf. primary instruction.

Semaphore

A mechanism for synchronizing and signalling between processes.

Set

A bit is set when its value is 1.

Sign extension

A signed value can be extended to occupy more bits by filling the most significant

bits with copies of the sign bit.

Sign bit

The most significant bit of a

signed value, used to indicate the sign of the value.

Signed value

Value which could be positive or negative depending on the

sign bit.

Sleep

The CPU is asleep when its clocks are turned off to reduce power consumption.

The CPU automatically goes to sleep after it becomes idle. It is woken by an

external

interrupt.

Slot

A slot is a field of a data structure for holding a value. A slot normally occupies one

word.

Stack

A stack is a data storage structure that uses a ‘first in, last out’ access model.

Adding an item to a stack is called pushing on, and extracting a value is called

popping. A program stack is normally implemented using the Wptr as the stack

pointer. The Areg, Breg and Creg form the

evaluation stack.

Stack, evaluation

See

evaluation stack.

State

The state of a process is the data needed for the process to continue execution.

This may include the evaluation stack, Iptr, Wptr, status register and local data.

Status register

The status register holds CPU status information which must be saved if an

interrupt occurs but is not saved if the process deschedules. Some status register

ST20-C1 Datasheet(PDF) 193 Page - STMicroelectronics

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