X3T9.2/88-009 REV 1
3 March 88

TO: John Lohmeyer, Chairman X3T9.2
    Dal Allan, Vice-Chairman X3T9.2

FROM: Dexter Anderson, Mike Eneboe      SMS

SUBJECT: TARGET MESSAGE RESPONSE CLARIFICATION

This  is  the  first revision to the  Message  Handling  Clarification 
memorandum that was submitted at the San Jose working group meeting. 

On Monday, February 22, the following people met to discuss this issue 
again,  Bill Spence,  Dave Skinner,  Jim McGrath,  Dave McIntyre, Paul 
Boulay, Gene Milligan, John Lohmeyer, Dal Allan and Dennis Appleyard.
This proposal is based on the results of that meeting.

The problem is the current message structure does not limit the length 
or  content of the messages the Initiator can send in the Message  Out 
phase as long as ATN is true.  
For  example  paragraph  5.1.10.2 MESSAGE OUT Phase says  "The  target 
shall handshake byte(s) in this phase until ATN goes false,  unless an 
error occurs (See MESSAGE REJECT, 5.5.2).".
This  does  not  specify what the target should do if  it  receives  a 
message such as SYNCHRONOUS DATA TRANSFER REQUEST but leaves ATN true.

The proposed solution is to specify when the initiator must negate ATN 
when in the MESSAGE OUT Phase.

The proposal is:
Paragraph 5.1.10.2 MESSAGE OUT PHASE
Replace  
"The  target  shall  handshake byte(s) in this phase  until  ATN  goes 
false, unless an error occurs (See MESSAGE REJECT, 5.5.2)."
with 
"The target shall handshake byte(s) in this phase until ATN goes false 
except when rejecting a message."

Paragraph 5.2.1 ATTENTION Condition
(This is just clean up)
Move the following words in paragraph "1." to paragraph "4.":
"but  before  the target asserts the REQ for any following MESSAGE  IN 
byte.  This permits a MESSAGE PARITY ERROR message from the  initiator 
to be associated with the appropriate message byte."

Add these paragraphs:
"After  the  target sends a MESSAGE REJECT message it shall switch  to 
the MESSAGE OUT phase again,if ATN is still asserted."

"The initiator must negate ATN before asserting ACK when  transferring 
the  last  byte of the following messages: BUS DEVICE  RESET,  MESSAGE 
PARITY ERROR, ABORT, MESSAGE REJECT, DISCONNECT, and any message  that 
requires negotiation, ie: SDTR and WIDE DATA TRANSFER REQUEST."

Paragraph 5.5.2 Messages
Remove the words ", regardless of the state of ATN." 
from ABORT, and BUS DEVICE RESET.

(This  just  clean  up.)  Remove  the  repeated  paragraphs  from  the 
description of the IDENTIFY message.
"Only one logical unit..."
"When sent from a target..."

Paragraph 5.5.5 SYNCHRONOUS DATA TRANSFER REQUEST Message (Optional)
Remove  the  paragraph  
"If  a  sequence of messages is received by a  target  without  parity 
error  during  continuous  assertion  of  ATN,  and  if  the  sequence 
comprises a responding SDTR message followed by an ABORT message,  the 
SDTR  message shall be executed prior to executing the ABORT  message. 
If  a  target  receives  the  ABORT message  prior  to  receiving  the 
responding SDTR message,  both devices shall go to  asynchronous  data 
transfer mode for data transfers between the two devices."
NOTE:  I am not sure if there is some meaning to this paragraph that I 
am  not aware of in which case it may need to be rewritten instead  of 
removed. What does an ABORT do to a previously agreed upon synchronous 
transfer request?