Request Sense and Ignore Wide Residue

Kendall, Guy GKENDALL at
Mon Aug 14 07:53:00 PDT 1995

I have noticed different behavior on two different wide drives I have and 
|from the spec
can't tell which one is correct, or if both are correct. It occurs when the 
initiator sends a
REQUEST SENSE command with an Allocation Length of 0x0D (13 decimal) to a 
target.  16-bit wide has been previously negotiated with an exchange of WDTR 

Since it's a 16-bit wide bus, only an even number of bytes can be 
transferred. One disk
drive transfers 0x0E (14 decimal) bytes and completes the I/O just fine. 
Since I only asked
for 0x0D (13 decimal) bytes, should I as an initiator know to throw away the 
last byte?
Or is the target acting improperly?

The second disk drive acts more like I would expect. This drive transfers 
0x0E (14 decimal)
bytes, but then sends me an IGNORE WIDE RESIDUE message to tell me to 
discard the
last byte transferred.

Which case is correct? Or are they both correct?

Guy Kendall - Software Development Engineer     Guy.Kendall at Symbios.COM
Symbios Logic, Inc. (Formerly NCR Microelectronics)
1635 Aeroplaza Drive                                 Voice: 719-573-3203
Colorado Springs, CO 80916                             Fax: 719-573-3289

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