Intel manual Endianness in Intel IXP400 Software, Basics of Endianness

Intel® IXP400 Software

Endianness in Intel® IXP400 Software

Endianness in Intel® IXP400 Software 27

27.1Overview

The Intel® IXP4XX Product Line of Network Processors and IXC1100 Control Plane Processor support Little-Endian (LE) and Big-Endian (BE) operations. This chapter discusses IXP400 software support for LE and BE operation.

This chapter is intended for software engineers developing software or board-support packages (BSPs) that are reliant on endianness support in the processor. The chapter is intended as an introduction to the most important facts regarding endianness as it relates to the IXP400 software.

A more detailed guide to endianness in the IXP42X product line is available in the application note, Intel® IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor: Understanding Big Endian and Little Endian Modes, which is freely available from the following Intel Developer Web site:

http://www.intel.com/design/network/products/npfamily/docs/ixp4xx.htm

Applicability to Specific Processors and Development Platforms

In general, the theories discuss in this chapter are applicable the entire IXP4XX product line. Each product generation does have some specific endianness related capabilities, as listed in “Silicon Versions” on page 352.

When discussing board-support package (BSP) issues for the Intel® IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor, this chapter refers to the Intel® IXDP425 / IXCDP1100 Development Platform. For the Intel® IXP46X Product Line of Network Processors, this chapter refers to the Intel® IXDPG465 Network Gateway Development Platform.

27.2The Basics of Endianness

Endianness is the numbering organization format of data representation in a computer. Endianness comes in two varieties: Big and Little. Little-Endian byte ordering assigns the lower byte address to the low eight bits of a 32-bit memory word, where Big-Endian byte order is the opposite. LE means that the least-significant byte of any multi-byte data field is stored at the lowest memory address, which is also the address of the larger field. See Figure 114.

All processors are either Big- or Little-Endian. Some processors, such as those in the IXP4XX product line and IXC1100 control plane processors, have a bit in a register that allows the programmer to select the desired endianness.

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	341