Cortex-A8 R2P2.pdf - ARM Information Center

Programmer’s Model2.10 Memory formatsThe processor views memory as a linear collection of bytes numbered in ascendingorder from zero. For example, bytes 0-3 in memory hold the first stored word, and bytes4-7 hold the second stored word.The processor can treat words in memory as either:• Byte-invariant big-endian format• Little-endian format.Additionally, the processor supports mixed-endian and unaligned data accesses. SeeChapter 4 Unaligned Data and Mixed-endian Data Support for details.NoteInstructions are always treated as little-endian.2.10.1 Byte-invariant big-endian formatIn byte-invariant big-endian format, the processor stores the most significant byte of aword at the lowest-numbered byte, and the least significant byte at thehighest-numbered byte. Therefore, byte 0 of the memory system connects to data lines31-24 as Figure 2-8 shows.BitHigher address31 24 23 16 15 8 7 0 Word address891011845674Lower address01230• Most significant byte is at lowest address• Word is addressed by byte address of most significant byteFigure 2-8 Big-endian addresses of bytes within words2.10.2 Little-endian formatIn little-endian format, the lowest-numbered byte in a word is the least significant byteof the word and the highest-numbered byte is the most significant. Therefore, byte 0 ofthe memory system connects to data lines 7-0. This is shown in Figure 2-9 on page 2-20.ARM DDI 0344E Copyright © 2006-2008 ARM Limited. All rights reserved. 2-19