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Sequence Status Register for 8259A Programmable Interrupt Controller Shadow Register

IP.com Disclosure Number: IPCOM000112663D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Matsushima, S: AUTHOR [+2]

Abstract

This article describes the sequence status register which contains the condition of the programming of an Intel 8259A programmable interrupt controller or an equivalent function. This function enables a personal computer system to get into a suspend mode or a hibernation during the programming of an Intel 8259A by notifying the system in which the register has been set in an Intel 8259A. A system program which takes care of a suspend/resume function can restore data to an Intel 8259A correctly when a personal computer system is resuming.

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Sequence Status Register for 8259A Programmable Interrupt Controller
Shadow Register

      This article describes the sequence status register which
contains the condition of the programming of an Intel 8259A
programmable interrupt controller or an equivalent function.  This
function enables a personal computer system to get into a suspend
mode or a hibernation during the programming of an Intel 8259A by
notifying the system in which the register has been set in an Intel
8259A.  A system program which takes care of a suspend/resume
function can restore data to an Intel 8259A correctly when a personal
computer system is resuming.

      Since an Intel 8259A has "write only" registers, a system which
supports a suspend/resume or a hibernation function must have shadow
registers which have the same data as an 8259A, if an 8259A is
powered off during a suspend mode.  And these registers in an 8259A
have a programming sequence in which all registers can be accessed
through two I/O addresses and a sequence of I/O port accesses decides
which register would be set.

      Fig. 1 shows the status change of the sequence status register
along with a programming sequence of an Intel 8259A.  The value of
the sequence status register is 00h at a power-on-reset, and it
changes at each step of the 8259A programming.  For example, if the
value of the sequence status register is 00h at resumption, the
system program restores the data to ICW1 and ICW2 (ICW3, ICW4 when
require...