Browse Prior Art Database

Subsystem Control Block Immediate Commands for the Micro Channel

IP.com Disclosure Number: IPCOM000106954D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 115K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+6]

Abstract

This article describes a technique for use in a personal computer system which utilizes registers for multiple purposes, thereby reducing the number of command registers in the MICRO CHANNEL* interface.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Subsystem Control Block Immediate Commands for the Micro Channel

       This article describes a technique for use in a personal
computer system which utilizes registers for multiple purposes,
thereby reducing the number of command registers in the MICRO
CHANNEL* interface.

      In the technique disclosed herein mechanism is defined within
the subsystem control block (SCB) architecture which provides a
command format that allows for command execution without requiring
additional storage fetches or additional I/O address space.  Separate
attention types are provided in the Attention Port which allow the
subsystem to treat the 32-bit value in the Command Port as the
command instead of a storage address.
IMMEDIATE COMMAND DELIVERY

      Immediate commands are mainly device directed and are control
oriented.  Like control block commands, immediate commands use the
Command and Attention ports for delivery.

      An Immediate command written to the Command and Attention ports
cannot be executed until the device has verified that the whole
command has been accepted by the subsystem.  After verify acceptance,
the Busy flag in the Command Busy/Status port will be set to zero.
The command type is determined by examining the Attention Code in the
Attention port.  When the command type is determined to be an
Immediate command type, the Operation Code in the Command port is
decoded to determine the device actions to be performed.

      An Immediate command may take one of two formats depending on
the value of Format Identifier (bit 8) in the Immediate command.  If
Format Identifier is set to zero, Format 0 is being used which allows
a command to use bits 16 - 31 for operation code-dependent purposes.
This gives the implementer additional flexibility.  When the Format
Identifier is set to one, Format 1 is being used which reserves bits
16 - 31 of the Immediate command.  This allows architecture defined
commands the flexibility to grow.  All commands described in this
document are Format 1.

      The figure shows the Immediate command formats.  The following
is a description of the fields of an Immediate command and their
meanings:
Bits 31 - 16   Refer to bit 8.
Bit 15         The disable-command-interrupt (DCI) bit specifies
whether the device requests an interrupt after successfully
completing this command. If this bit is set to 1, the device does not
request a system interrupt.  If this bit is set to 0, the device
requests an interrupt after completing the command and reports the
status to the Interrupt Status port.  For some commands, the bit is
ignored.
Bit 14         The disable-device-interrupt (DDI) bit specifies
whe...