ST20-C1 datasheet(101/205 Pages) STMICROELECTRONICS

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8 Instruction Set Reference

dequeue

dequeue a process

Code: 23 F8

Description: Load into Breg a pointer to the first process from the queue control

block pointed to by Areg. Load into Areg a boolean value indicating whether a

process was found. The queue control block is defined in Chapter 7.

Definition:

if (frontptr = NotProcess)

-- queue is empty

{

Areg

′← false

Breg

′← undefined

}

else

-- queue is not empty

{

Areg

′← true

Breg

′← frontptr

if (frontptr = backptr)

-- one process on queue

word

′[Areg @ q.FPtrLoc]← NotProcess

else

-- many processes on queue

word

′[Areg @ q.FPtrLoc]← word[ frontptr @ pw.Link ]

}

Creg

′← undefined

where frontptr = word[Areg @ q.FPtrLoc]

backptr = word[Areg @ q.BPtrLoc]

Status Register:

No effect

Comments:

Secondary instruction.

This instruction may require 4 memory accesses. If the queue structure is in off-

chip memory then interrupt latency may be affected.

Areg must be word aligned (i.e. divisible by 4).

ST20-C1 Datasheet(PDF) 101 Page - STMicroelectronics

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