[t13] Fwd: why not H = C = D ModeSense6 for just the header

Eschmann, Michael K michael.k.eschmann at intel.com
Wed Feb 12 10:52:36 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* "Eschmann, Michael K" <michael.k.eschmann at intel.com>
*
Hi Jim,

I'll leave the tape domain to you, but I've seen many CD-ROM's fail on the 6-byte format.  It may not fail on all, which may be why you see them working fine.

6-byte mode sense:
    struct _MODE_SENSE {
        UCHAR OperationCode;
        UCHAR Reserved1 : 3;
        UCHAR Dbd : 1;
        UCHAR Reserved2 : 1;
        UCHAR LogicalUnitNumber : 3;
        UCHAR PageCode : 6;
        UCHAR Pc : 2;
        UCHAR Reserved3;
        UCHAR AllocationLength;
        UCHAR Control;
    } MODE_SENSE, *PMODE_SENSE;

10-byte mode sense:
    struct _MODE_SENSE10 {
        UCHAR OperationCode;
        UCHAR Reserved1 : 3;
        UCHAR Dbd : 1;
        UCHAR Reserved2 : 1;
        UCHAR LogicalUnitNumber : 3;
        UCHAR PageCode : 6;
        UCHAR Pc : 2;
        UCHAR Reserved3[4];
        UCHAR AllocationLength[2];
        UCHAR Control;
    } MODE_SENSE10, *PMODE_SENSE10;

You'll see that the allocation length (or Parameter List Length)data doesn't line up, so good drivers will convert from 6-to-10 and pad the CDB out (with zeros) to a 12 or 16 byte CDB so bad drives (many, I suppose) will function.



-----Original Message-----
From: James.C.Hatfield at seagate.com [mailto:James.C.Hatfield at seagate.com]
Sent: Tuesday, February 11, 2003 3:32 PM
Cc: forum at t13.org; t10 at t10.org
Subject: RE: [t13] Fwd: why not H = C = D ModeSense6 for just the header


This message is from the T13 list server.



Most ATAPI tape drives understand the 6-byte CDB.
Some support the 10-byte format, as well.

ATAPI CD-ROM  drives support 6- and 10-byte forms.

The act of supporting the 10-byte CDB implies to <some> drivers that the
device
is a CD-ROM type of device.... leading to the driver getting confused.

Halve Phun !!!
-----------------------------------------------------------------
Jim Hatfield
ATA Interface Firmware & T13 (ATA/ATAPI) Standards Representative
Seagate Technology - PSG
   e-mail:  James.C.Hatfield at seagate.com
   s-mail:  389 Disc Drive;  Longmont, CO 80501 USA
   voice:   720-684-2120
   fax    :    720-684-2711
====================================================


                                                                                                                                                     
                    "Eschmann, Michael                                                                                                               
                    K"                          To:     <t10 at t10.org>, <forum at t13.org>                                                               
                    <michael.k.eschmann@        cc:                                                                                                  
                    intel.com>                  Subject:     RE: [t13] Fwd: why not H = C = D ModeSense6 for just the header                         
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This message is from the T13 list server.


FYI, this is an issue with the Microsoft driver (supplied with their
Windows 2000 OS) is not converting the SCSI 6-byte CDB to the 10-byte CDB
format.  ATAPI drives don't understand the 6-byte format of "Mode Sense"
(am I wrong?), so I believe this issue that MS reported has nothing to do
with odd "byte" issues that you've been, er, peddling.  MKE.



-----Original Message-----
From: Pat LaVarre [mailto:LAVARRE at iomega.com]
Sent: Monday, February 10, 2003 8:22 AM
To: t10 at t10.org; forum at t13.org
Subject: [t13] Fwd: why not H = C = D ModeSense6 for just the header


This message is from the T13 list server.


Newsgroups: microsoft.public.vc
Date: 2003-02-07 13:39:51 PST
...
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q813908
SCSI Pass-Through Mode Sense Command May Crash the Computer
...
If a SCSI Mode Sense command (operation code 0x1A) is
sent by using SCSI pass-through to an ATAPI CD-ROM
device, you may receive a "Stop" error message on a
blue screen and the computer may then stop responding
or may restart.  This may occur if the value of the
Data Length field in the Mode Sense command is less
than 8.  Note that this problem occurs only with the
6-byte Mode Sense command (operation code 0x1A), not
with the 10-byte Mode Sense command (operation code
0x5A).
...

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