PFA Rev 03 (94-190r3)

George Penokie GOP at RCHVMP3.VNET.IBM.COM
Tue Nov 29 07:33:22 PST 1994


What follows is the text version of rev 3 of the PFA proposal (94-190r3).
I will place a framemaker and a postscript version on the SCSI BBS.  Rev 03
has allso been placed in the mailing you will be recieving in the next few
weeks.


Date:  Nov. 21,1994

To:  X3T10 Committee (SCSI)

From:  George Penokie (IBM)

Subject:  Exception Handling Selection Mode Page

1 Overview

Many of today SCSI devices have asynchronous events that occur.
These devices use several different methods for reporting asynchronous
events. This proposal allows a method for application clients to select the
method it expects the target to use when reporting asynchronous events.

This proposal also define parameters to control reporting of failures that
are predicted by a target.

It is recommended that the informational exceptions control page be
added to the following command :standards:

SCSI-3 Block Commands Standard [X3T10/996D]

SCSI-3 Stream Commands Standard [X3T10/997D]

SCSI-3 Medium Changer Commands Standard [X3T10/999D]

SCSI-3 Controller Commands [X3T10/1047D]

SCSI-3 Muiti-Media Commands Standard [X3T10/1048]

It is recommended that the information exceptions control page be added
to the following SCSI device types:

Direct-access device (e.g. magnetic disk)

Sequential-access device (e.g. magnetic tape)

Printer device

Write-once device (e.g. some optical disks)|

CD-ROM device

Optical memory device (e.g. some optical disks)

Medium changer device (e.g. jukeboxes

Communications device

2 Informational exceptions control page

The informational exceptions control page defines the methods used by
the target to control the reporting and the operations of specific
informational exception conditions. This page shall only apply to
informational exceptions that report an additional sense code of FAILURE
PREDICTION THRESHOLD EXCEEDED to the application client.

Informational exception conditions occur as the result of vendor specific
events within a target. An informational exception condition may occur
asynchronous to any commands issued by an application client.



Table 1 - Informational exceptions control page

 Bit

Byte

7

6

5

4

3

2

1

0

0

PS

Reserved

Page code (1Ch)

1

Page length (0eh)

2

perf

Reserved

dexcpt

Reserved

LogErr

3

Reserved

Method of reporting informational
exceptions

4

MSB

 interval timer

5

6

7

LSB

8

MSB

report count

9

10

11

LSB

The log errors bit (logerr) of zero indicates that the logging of
informational exception conditions within a target is vendor specific. A
logerr bit of one indicates the target shall log informational exception
conditions.

The method of reporting informational exceptions field (see table 2)
indicates the methods that shall be used by the target to report
informational exception conditions. The priority of reporting multiple
information exceptions is vendor specific.



Table 2 - Format of method of reporting informational exceptions field

Code

Description

0h

No reporting of informational exception condition

This method
instructs the target to not report information exception conditions. The target
shall not preserve informational exception(s) information for reporting
reasons.

1h

Asynchronous event reporting

This method instructs the target to report
informational exception conditions by using the rules for asynchronous event
reporting as described in the SCSI-3 Architecture Model and the relevant
Protocol Standard.

The sense key shall be set to RECOVERED ERROR and the additional
sense code shall be indicate the cause of the informational exception
condition.

2h

Generate unit attention

This method instructs the target to report
informational exception conditions by issuing a unit attention condition on
any command. In response to a REQUEST SENSE command the target
shall return sense data. The sense key shall be set to UNIT ATTENTION
and the additional sense code shall be indicate the cause of the
informational exception condition.

The command that has the CHECK CONDITION shall not be executed
before the informational exception condition is reported.

3h

Conditionally generate recovered error:

This method instructs the target
to report informational exception conditions, dependent on the value of the
per bit of the error recovery parameters mode page, by returning a sense of
CHECK CONDITION on any command. In response to a REQUEST SENSE
command the target shall return sense data. The sense key shall be set to
RECOVERED ERROR and the additional sense code shall be indicate the
cause of the informational exception condition.

The command that has the CHECK CONDITION shall complete without
error before any informational exception condition may be reported.

4h

Unconditionally generate recovered error:

This method instructs the
target to report informational exception conditions, regardless of the value of
the per bit of the error recovery parameters mode page, by returning a
sense of CHECK CONDITION on any command. In response to a
REQUEST SENSE command the target shall return sense data. The sense
key shall be set to RECOVERED ERROR and the additional sense code
shall be indicate the cause of the informational exception condition.

The command that has the CHECK CONDITION shall complete without
error before any informational exception condition may be reported.

5h

Generate no sense:

This method instructs the target to report informational
exception conditions by returning a sense of CHECK CONDITION on any
command. In response to a REQUEST SENSE command the target shall
return sense data. The sense key shall be set to NO SENSE and the
additional sense code shall be indicate the cause of the informational
exception condition.

The command that has the CHECK CONDITION shall complete without
error before any informational exception condition may be reported.

6h

Only report informational exception condition on request

This method
instructs the target to preserve the informational exception(s) information. To
find out about information exception conditions the Application Client polls
the target by issuing a REQUEST SENSE command when the target does
not have a pending check condition. In response to a REQUEST SENSE
command the target shall return sense data. The sense key shall be set to
NO SENSE and the additional sense code shall be indicate the cause of the
informational exception condition.

7h-Bh

Reserved

Ch-Fh

Vendor specific

A disable exception control (dexcpt) bit of zero indicates information
exception operations shall be enabled. The reporting of information
exception conditions when the dexcpt bit is set to zero is determined
|from the method of reporting informational exceptions field. A
dexcpt bit of one indicates the target shall disable all information
exception operations. The method of reporting informational
exceptions field is ignored when dexcpt is set to one.

A performance bit (perf) of zero indicates that informational exception
operations that are the cause of delays are acceptable. A perf bit of one
indicates the target shall not cause delays while doing informational
exception operations.

Note 1  A perf bit set to one may cause the target to disable some
or all of the informational exceptions operations, thereby limiting the
reporting of informational exception conditions.

The interval timer field indicates the period in 100 millisecond
increments for reporting that a informational exception condition has
occurred. The target shall report the informational exception condition as
soon as possible after the timer interval has elapsed. After the
informational exception condition has been reported the interval timer
shall be restarted. A value of zero in the interval timer field indicates
that the target shall only report the informational exception condition one
time. A value of FFFFFFFFh in the interval timer field shall indicate the
timer interval is vendor specific.

The report count field indicates the number of times to report an
informational exception condition to the application client. A value of zero
in the report count field indicates there is no limit on the number of
times the target shall report an informational exception condition.

The maintaining of the interval timer and the report count access power
cycles and/or resets by the target shall be vendor specific.




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