ST20-C1 datasheet(153/205 Pages) STMICROELECTRONICS

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8 Instruction Set Reference

stop

stop process

Code: 23 F4

Description: Terminate the current process, saving the current Iptr and Wptr for later

use, and start the next process from the scheduling queue. If the scheduling queue is

empty then the CPU will become idle. This instruction is implemented in two stages to

protect interrupt latency. The first stage deschedules the current process and sets the

start_next_task status bit. The second stage clears the start_next_task status bit

and starts the next process. An interrupt may occur between the two stages.

Definition:

if (

stop trap handler installed)

take stop trap

else

{

word

′[Tdesc @ pw.Iptr]

← next instruction

word

′[Tdesc @ pw.Wptr]

← Wptr

Status

′

local_interrupt_enable

← set

Status

′

overflow

← clear

Status

′

undeflo w

← clear

Status

′

carry

← clear

Status

′

interrupt_mode

← clear

Status

′

trap_mode

← clear

Status

′

start_next_task

← clear

Status

′

timeslice_count

← MaxTimesliceCount

-- start next process on scheduling queue

if (frontptr = NotProcess)

-- queue is empty, so become idle

{

Status

′

sleep

← set

Status

′

user_mode

← clear

if (

idle trap handler installed)

take idle trap

else

set idle

}

else

-- processes waiting, so start next process

{

Status

′

sleep

← clear

Status

′

user_mode

← set

Tdesc

′← frontptr

Wptr

′← word [frontptr @ pw.Wptr]

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