Parity Handling in MSG-IN

George Penokie gop at us.ibm.com
Thu Sep 26 08:51:01 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* George Penokie <gop at us.ibm.com>
*




Jorge,
If the target goes to status phase then the current command is complete. If
the status is a check condition then that command failed. The target will
not, for any reason, continue a command after it returns status. However, a
parity error occurring on a message does not automatically cause the target
to go to a status phase.

Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880




                                                                                                                                         
                      "Monterrosa, Jorge"                                                                                                
                      <Jorge_Monterrosa at a        To:       George Penokie/Rochester/IBM at IBMUS, "Monterrosa, Jorge"                       
                      daptec.com>                 <Jorge_Monterrosa at adaptec.com>                                                         
                      Sent by:                   cc:       owner-t10 at t10.org, "'t10 at t10.org'" <t10 at t10.org>                              
                      owner-t10 at t10.org          Subject:  RE: Parity Handling in MSG-IN                                                 
                                                                                                                                         
                                                                                                                                         
                      09/26/02 09:52 AM                                                                                                  
                                                                                                                                         
                                                                                                                                         



* From the T10 Reflector (t10 at t10.org), posted by:
* "Monterrosa, Jorge" <Jorge_Monterrosa at adaptec.com>
*
George:

Perhaps the wording for my second question was incorrect. What I meant is:
In a parity during a MSG-IN phase, if the target goes to the status phase
after receiving the MSG-OUT 09, issuing a check condition status. Does the
initiator has to process the status phase as an error condition or it just
has to let the target to finish the I/O and then respond to the check
condition with a request sense command.

Jorge Monterrosa


-----Original Message-----
From: George Penokie [mailto:gop at us.ibm.com]
Sent: Thursday, September 26, 2002 6:56 AM
To: Monterrosa, Jorge
Cc: owner-t10 at t10.org; 't10 at t10.org'
Subject: Re: Parity Handling in MSG-IN






Jorge,
In SPI-5 rev 3 the following two sections are the location for the rules
you requested in Q1. Your Q2 does not make sense. If a target reports it
received a parity error then it received a parity error. Even if it really
did not but says it did then it will behave as if it did so the initiator
will have to respond as if the parity error occurred.

10.11.3 MESSAGE IN phase exception condition handling
If the SCSI initiator port detects a parity error on any message byte it
receives the SCSI initiator port shall
create an attention condition. When the SCSI target port switches to a
MESSAGE OUT phase the SCSI
initiator port shall send a MESSAGE PARITY ERROR message (see 16.3.7) to
the SCSI target port. This
message notifies the SCSI target device that the message in byte was
invalid.

16.3.7 MESSAGE PARITY ERROR
The MESSAGE PARITY ERROR message is sent from the SCSI initiator port to
the SCSI target port to
indicate that it received a message byte with a parity error (see 10.11.5).
In order to indicate its intentions of sending this message, the SCSI
initiator port shall create an attention
condition on the message byte that has the parity error. This provides an
interlock so that the SCSI target
port is able to determine which message byte has the parity error. If the
SCSI target port receives this
message under any other circumstance, it shall signal a catastrophic error
condition by going to a BUS
FREE phase without any further information transfer attempt (see 10.2).
If the SCSI target port attempts a retry after receiving the MESSAGE PARITY
ERROR message the SCSI
target port shall return to the MESSAGE IN phase before switching to some
other phase, the SCSI target
port shall resend the entire message that had the parity error..


Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880






                      "Monterrosa, Jorge"

                      <Jorge_Monterrosa at a        To:       "'t10 at t10.org'"
<t10 at t10.org>
                      daptec.com>                cc:

                      Sent by:                   Subject:  Parity Handling
in MSG-IN
                      owner-t10 at t10.org





                      09/26/02 07:47 AM








* From the T10 Reflector (t10 at t10.org), posted by:
* "Monterrosa, Jorge" <Jorge_Monterrosa at adaptec.com>
*
I have two questions in regard to parity handling: The first question is:
Reading some SCSI books I found that if  a parity error condition occurs in
MSG-IN phase the initiator must inform the target of the parity error by
asserting the ATN signal and issuing MSG-OUT 09  and the target should
re-send the byte after the MSG-OUT phase. My question is where does the
SCSI
spec mention that statement.
The second question is: if the target wrongly reports the parity by issuing
a check condition, how does the initiator has to react to the incorrect
respond from the target.

Thanks.

Jorge Monterrosa
FTL Adaptec Corp.
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