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Using XScales Big Endian Mode to Increase Embedded iSCSI System Performance

IP.com Disclosure Number: IPCOM000008842D
Publication Date: 2002-Jul-17
Document File: 3 page(s) / 43K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for using XScales Big Endian mode to increase embedded iSCSI system performance. Benefits include a reduction in data caching and the elimination of byte swapping for variables longer than one byte.

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Using XScale’s Big Endian Mode to Increase Embedded iSCSI System Performance

Disclosed is a method for using XScale’s Big Endian mode to increase embedded iSCSI system performance. Benefits include a reduction in data caching and the elimination of byte swapping for variables longer than one byte.

Background

Currently, most network protocols use Big Endian order for memory arrangement, and many embedded processors use Little Endian order. This means that any data item which is larger than eight-bit long (a byte), such as word (two bytes) or double word (four bytes) must be reordered before being sent on the wire. The following table outlines the variables in the iSCSI header:

Number of bytes

Kind of variable

2

  • ISID (Initiator Session ID)
  • TSID (Target Session ID)
  • CID (Connection ID)
  • Time2Wait
  • Time2Retain

3

  • DataSegmentLength

4

  • Initiator Task Tag
  • CmdSN (Command Serial Number)
  • ExpStatSN (Expected status Serial Number)
  • StatSN (Status Serial Number)
  • ExpCmdSN (Expected Command Serial Number)
  • MaxCmdSN(Maximum Command Serial Number)
  • BegRun (Begin of the Run)
  • RunLength (Length of the Run)
  • DataSN (Data Serial Number)
  • Target Transfer Tag

 

8

  • LUN

Since iSCSI protocol is built on the top of TCP/IP protocol, all variables in TCP, IP, and UDP headers larger than 1 byte must be reordered before being sent on the wire. There are some two- byte and four-byte variables in the IP header, TCP header, and UDP header. Figure 1 shows the IP header in Big Endian order and Figure 2 shows the IP header in Little Endian order.

In the above examples, “Total Length”, “Identification” and “Header Checksum” fields are in Little Endian order after the XScale pr...