Browse Prior Art Database

Combined Arbitration, Selection/Reselection, Message, and Command Function for Small Computer System Interface

IP.com Disclosure Number: IPCOM000113916D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 167K

Publishing Venue

IBM

Related People

Cook, DC: AUTHOR [+5]

Abstract

Disclosed is a SCSI-2 (Small Computer System Interface, version 2) MicroChannel* adapter in which an ASR Arbitration, Selection/Reselection (ASR) state machine combines several SCSI operations into a single state machine and interrupt. The adapter is operated in an initiator mode and in a target mode. In the initiator mode, the Arbitration, Selection, Message Out and Command protocols are combined into one state machine producing a single interrupt. In the target mode, the Arbitration, Reselection, and Message In protocols are combined into the same state machine producing the same interrupt.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 27% of the total text.

Combined Arbitration, Selection/Reselection, Message, and Command
Function for Small Computer System Interface

      Disclosed is a SCSI-2 (Small Computer System Interface, version
2) MicroChannel* adapter in which an ASR Arbitration,
Selection/Reselection (ASR) state machine combines several SCSI
operations into a single state machine and interrupt.  The adapter is
operated in an initiator mode and in a target mode.  In the initiator
mode, the Arbitration, Selection, Message Out and Command protocols
are combined into one state machine producing a single interrupt.  In
the target mode, the Arbitration, Reselection, and Message In
protocols are combined into the same state machine producing the same
interrupt.

      Before the functions of the ASR state machine are enabled,
several registers must be programmed with information.  The ID
(Identifier) for the SCSI chip and the ID of the device to be
selected or reselected must be loaded into the SCSI Select ID (1Ah)
Register.  The message byte(s) must also be programmed into the
Message Byte Registers (1Ch-21h), starting with the first byte at
Message Byte O (1Ch).  The ASR can automatically send up to six
message bytes.  If the ASR is in the initiator mode, which is the
default mode, a command of up to twelve bytes may be loaded into the
Command Byte (24h-2Fh) Registers, starting with the first byte at
Command Byte O (24h).  After the ID message and the command bytes
have been loaded, the ASR Control Register (18h) may be programmed.
The message length and command length are set in the high byte of the
ASR Control Register.  The respective counts decrement as each byte
is handshaked through the SCSI bus, providing information which is
useful if an error occurs during any of the handshakes.  By setting
the Start SMI bit, the Status and Message In function will
automatically be enabled following a successful selection by the ASR
function.  The lower byte of the ASR Control Register contains four
status bits and four programmable function bits.  The ASR Start bit
enables the ASR state machine.  The ASR halt bit allows the ASR
function to be stopped if the ASR is not in an arbitration phase.
The Target Mode Bit differentiates between target and initiator modes
of operation.  The Long Message Bit tells the ASR function that the
message is longer than the allotted six bytes.

      When the state machine is enabled, it waits in an idle state
for a valid Bus Free phase.  After a bus free delay, the ASR asserts
BSY and its Data Bus ID bit, and waits through an arbitration delay
before examining the bus for a "Win".  If the ASR loses the
Arbitration it releases BSY and its Data Bus ID bit, returning to the
idle state, in which it waits to participate in the next Arbitration
phase.  If the ASR wins the Arbitration, it asserts SEL and waits
through a bus clear delay for the losers to release BSY and their ID
bits.

      After a bus clear delay, together with a bus settl...