Field pointer sense key specific data (SPC4 -> Sense data -> Descriptor format sense data)
Alex.Mohandas at emc.com
Alex.Mohandas at emc.com
Tue Aug 23 06:35:58 PDT 2011
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1108231_f.htm">HTML-formatted message</a>
I am of the opinion that RESERVED fields should be treated as separate
individual bits that are RESERVED.
This is because, in future, if a new feature is implemented by taking up a
single bit from any of these RESERVED fields and if you have implemented
RESERVED field as 'multiple bit field', then wrong information will be sent
in the SENSE KEY SPECIFIC field.
Thanks & Regards,
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of srivatsa h.c.
Sent: Tuesday, August 23, 2011 5:52 PM
To: t10 at t10.org
Subject: Field pointer sense key specific data (SPC4 -> Sense data ->
Descriptor format sense data)
Following is the issue that I am facing with "Field pointer sense key
specific data". It would be of great help if you could give your inputs on
Whenever a command results in "Check condition", then according to SPC4r29 :
1) The sense key specific sense data descriptor (see table 30) provides
additional information about the exception
condition described in 22.214.171.124. The format and content of the sense-key
specific data depends on the value in the
SENSE KEY field (see 126.96.36.199).
2) If the sense key is ILLEGAL REQUEST, then the SENSE KEY SPECIFIC field
shall be as shown in table 32.
According to table 32, "Field pointer sense key specific data" is a 3 byte
value. In byte 0, there is 3 bit value called BIT POINTER and according to
SPC4, the description for BIT POINTER is as follows:
3) A bit pointer valid (BPV) bit set to zero indicates that the value in the
BIT POINTER field is not valid. A BPV bit set to
one indicates that the BIT POINTER field specifies which bit of the byte
designated by the FIELD POINTER field is in
error. When a multiple-bit field is in error, the BIT POINTER field shall
point to the first bit (i.e., the left-most bit) of the
The issue is with sentence that is underlined and in italics above "When a
multiple-bit field is in error, the BIT POINTER field shall point to the
first bit (i.e., the left-most bit) of the
For e.g., in READ10 command, 6th byte, bit7:bit6:bit5 are RESERVED. Should
this field be treated as a single "multiple bit field" or 3 separate
individual bits which are reserved?
CASE 1: The 3 bits are considered as single "multiple bit field"
If this field(bit7:bit6:bit5 which is reserved) is set to non zero value,
then the disk returns Check Condition, with Field Pointer set to 6 and Bit
Pointer set to 7.
CASE 2: The 3 bits are considered as 3 separate individual bits
Field pointer will be set to 6 and Bit pointer will be set to the bit that is
in error. For e.g. if 001b is set, then the bit pointer will point to 5. If
100b is set, then the bit pointer will point to 7.
Which one of the above 2 cases is correct?
Please let me know if any additional information is required.
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