X3T9.2/87-83



To:       John Lohmeyer -- Chairman X3T9.2

From:     Anthony Kozlowski

Subject:  Certification Pattern Page 6 of Mode Select/Sense

Date:     May 18, 1987



The purpose of this memo is to present a method of 
communicating Certification Data from the Host to the Device.  
This method is a modification of the same function that was 
presented in CCS Rev. 4A, and is intended to be an 
alternative to the method that would have this information 
transferred in the Data Phase in a FORMAT UNIT command.

Allowing Certification Data to be transferred as a MODE SELECT 
Page has the following benefits:

     1. It is consistant with the SCSI concept surrounding 
        the FORMAT UNIT command of:

        -- Reserve Unit;
        -- Mode Sense;
        -- Mode Select;
        -- Format Unit;
        -- Release Unit;

     2. It had been introduced in CCS.  Some devices have been 
        designed with this capability in this Page.

     3. Only one type of data is transferred during the Data 
        Phase of a FORMAT UNIT command (the D list of 
        defects).

     4. The MODE SENSE/SELECT commands already have the Page 
        concept built in.


In order to be general in nature, the Certification Pattern 
may be a variable length; therefore, the concept of a Variable 
Length MODE SENSE Page must be introduced.  This has been done 
by designating a Reserved bit adjacent to the Page Code Value 
to be the Variable Length Page Indicator.  It is set to 1 by 
the Target whenever a MODE SENSE command, Page Control Field = 
Report Changeable Values, to indicate that the Page Length 
field, and hence the Length of the Page, is variable.

The following text is to be added or changed to the SCSI-2 
document, X3T9.2/86-109 Rev. 1, dated April 15, 1987:

p. 8-21  Table 8-18: Page Codes for Direct-Access Devices

     Code           Description
     ------------------------------------------------------
     06h            Certification Pattern
     07h - 09h      Reserved


p. 8-40a  Table 8-XX: Certification Pattern

==============================================================
  Bit|   7  |   6  |   5  |   4  |   3  |   2  |   1  |   0  |
Byte |      |      |      |      |      |      |      |      |
==============================================================
 0   |  VAR  |  Res  |        Page Code (06h)                |
-----|-------------------------------------------------------|
 1   |                        Parameter Length (M)           |
-----|-------------------------------------------------------|
 2   |                        Reserved                       |
-----|-------------------------------------------------------|
 3   |                        Pattern Type                   |
-----|-------------------------------------------------------|
4-N  |                        Certification Pattern          |
==============================================================

This Page is intended to provide the data pattern to be used 
by the Target to fill the Data Fields during the FORMAT UNIT 
command.

If a command other than a FORMAT UNIT command follows the 
MODE SELECT command that contains this Page, the 
Certification Data provided by this page may not be retained 
by the Target.

The VAR field must be set to 1 whenever a MODE SENSE command, 
Page Control Field = Report Changeable Values, is executed, 
to indicate that this Page is a Variable Length Page.

The Parameter Length field contains the value of the number 
of bytes within this Page that follow this byte.  It is a 
variable, depending on the length of the Certification 
Pattern.  It has a value of: 
          Length of Certification Pattern + 2.  

During the execution of a MODE SENSE command, Page Control 
Field = Report Changeable Values, the value of the Parameter 
Length field shall be 3.
The Pattern Type field defines the type of pattern that is 
enumerated in the Certification Pattern.  The values for this 
field are:

     Pattern Type        Description
     ------------------------------------------------------------
        00h              Reserved;
        01h              Repeating Pattern, repeats the 
                         Certification Pattern as many times 
                         as necessary to fill the data block;
        02h              Variable Pattern, starts with the 
                         Certification Pattern, and 
                         increments the value until the data 
                         block is filled;
        03h              Logical Block Pattern, repeats the 
                         4-byte Logical Block address of the 
                         block, until the data block is 
                         filled;
        04h - 7Fh        Reserved;
        80h - FFh        Vendor Unique.

The Certification Pattern byte(s) contain the data, or the 
seed for the data, that is used during the FORMAT UNIT 
command.


Thank you for your consideration in this matter.

Sincerely,




__________________________

A. Kozlowski