Re: iSCSI CRC check clarification

["Julian Satran" <Julian_Satran@il.ibm.com>]

Tandra,

I am not sure I understand what you are talking about.
The spec clearly states how the CRC should be calculated and what the bit 
order on the wire is.
Perhaps by "reflecting" you are talking about the later.
The examples where checked independently by me and at least 2 other 
persons.

Regards,
Julo




"De, Tandra" <Tandra_De@adaptec.com>
31-10-01 00:08
Please respond to "De, Tandra"

 
        To:     Julian Satran/Haifa/IBM@IBMIL
        cc:     "'ips@ece.cmu.edu'" <ips@ece.cmu.edu>, "De, Tandra" 
<Tandra_De@adaptec.com>
        Subject:        iSCSI CRC check clarification

 



Julian,
 
I followed few iSCSI  CRC checking example threads and the thread file://www.pdl.cmu.edu/mailinglists/ips/mail/msg05931.html says  that "Before transmission, the CRC bits must be reflected and 
complemented";  whereas, the iscsi- 08 draft only mentions about 
complementing the CRC before  transmission. So attached you will find two 
software implementation code  examples: crc_reflect.cpp and 
crc_no_reflect.cpp. 
I ran few test cases  with the attached example code and when I do reflect 
bits I  get
                                 0:        ff ff ff  ff
                                 4:        ff ff ff  ff
                                 8:        ff ff ff  ff
                                12:        ff ff ff  ff
                                16:        ff ff ff  ff
                                20:        ff ff ff  ff
                                24:        ff ff ff  ff
                                28:        ff ff ff ff
 
                                32:        43 ab a8 62
in the transmission  side, and the reception side I get 0x1c2d19ed.
 
But when I do not  bit flip I get

                                 0:        ff ff ff  ff
                                 4:        ff ff ff  ff
                                 8:        ff ff ff  ff
                                12:        ff ff ff  ff
                                16:        ff ff ff  ff
                                20:        ff ff ff  ff
                                24:        ff ff ff  ff
                                28:        ff ff ff ff
 
                                32:        46 15 d5 c2
in the transmission  side, and the reception side I do get 0x1c2d19ed 
though. 
 
I like to clarify  which implementation we should use so that both 
Initiator and Target will be in  sync. validating the CRC. I appreciate if 
you could verify the attached files to  see I am missing anytbing. Also I 
think that it would help everyone who are  dealing with iSCSI CRC if you 
could put up the finalized version of the code in  the reflector.
 
Thanks,
Tandra (tde@corp.adaptec.com)



#### crc_no_reflect.cpp has been removed from this note on October 31 2001 
by Julian Satran
#### crc_reflect.cpp has been removed from this note on October 31 2001 by 
Julian Satran