SSA-S2P mode page proposal

scheible at VNET.IBM.COM scheible at VNET.IBM.COM
Fri Aug 11 09:31:06 PDT 1995

Ladies and gentlemen,
   Attached is a proposal to add clarification on several mode pages
and how they are defined in SSA-S2P.  The end of the proposal is
identified by ***END OF PROPOSAL*** to indentify truncation of email.
   I have copied the SSA and SCSI reflectors.  Sorry about duplication.

John Scheible
scheible at
Accredited Standards Committee
X3, Information Processing Systems
                                         Doc:  X3T10.1/95a172r0
                                         Date: August 11, 1995
                                         Project:  X3T10.1 / 1121D
                                         Ref Doc.: SSA-S2P rev 3
                                         Reply to: John Scheible
To:       X3T10.1 Membership
From:     John Scheible
Subject: Mode page changes proposal for SSA-S2P

Several mode page parameters either do not apply to SSA-S2P, or have
different meanings.  This proposal addresses these differences.

The following options were chosen to minimize device driver changes
when converting from parallel SCSI-2 to SSA-S2P.
  a) In page 02h (Disconnect/Reconnect parameters) the maximum burst
     size field could be used to limit the byte count field in any
     associated DATA READY or DATA REQUEST SMS.  However, I chose to make
     all parameters ignored due to the ease in changing the byte count
     field in the DATA REPLY SMS (read) and by pausing the data transfer
     for a write (by the initiator).  If there are strong performance
     advantages to hardware controlled data transfer, then we could
     reconsider it.
  b) I chose to have the ignored parameters still be saved and echoed
     back with the Mode Sense command.
  c) I chose not to specify the initial or changeable parameters.

Add a new section 7.7 under clause 7 (Some differences between SSA
SCSI-2 Protocol and parallel SCSI-2) as shown on the following page.


John Scheible
Voice:    (512) 823-8208
FAX:      (512) 823-0758
Email:    Scheible at
7.7   Mode page parameter differences

Several of the parallel SCSI-2 mode page parameters need to be
redefined for SSA-S2P.

7.7.1   Page 02h - Disconnect/Reconnect parameters

The SCSI-2 Disconnect/Reconnect parameters page is not required by SSA
due to the frame multiplexing nature of the link.  The page is
supported, but all parameters contained within the page are ignored.
The ignored parameters include the following parameters.
  a) read buffer full ratio
  b) write buffer full ratio
  c) bus inactivity limit
  d) disconnect time limit
  e) connect time limit
  f) maximum burst size
  g) dtdc

The target shall return the Page 02h parameters in the Mode Sense
command that were issued with the Mode Select command, according to
the rules regarding current and saved values.  SSA-S2P does not
specify what values the parameters shall be initialized to, nor does
SSA-S2P specify which parameters are changeable.

7.7.2   Page 0Ah - Control Mode parameters

Since the optional concept of Extended Contingent Allegiance (ECA) is
not supported by SSA-S2P, the following parameters are fixed in Page
0Ah (Control Mode parameters).  These parameters are initialized to
the specified values and are not changeable.
  a) eeca bit = 0b
  b) raenp bit = 0b
  c) uaaenp bit = 0b
  d) eaenp bit = 0b
  e) ready aen holdoff period field = 0000h

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