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Byte swapping of data is a natural consequence of address invariance. It occurs when data in one endian format is read by a system that uses the other endian format. For example, suppose the DMA descriptor values initialized by the code shown in Listing A-1 are generated by a little-endian system and saved to disk. The data is then read from the disk by a big-endian system.
Assume that the data is written to disk in byte-address order, and that the disk memory is formatted in an 8-byte wide configuration. The little-endian disk memory image would look like Figure A-5.
Figure A-5 Little-endian memory image
When read by a big-endian system in byte-address order, the data would be stored in memory as shown in Figure A-6.
Figure A-6 Big-endian memory image
Notice that the byte offsets of each field are still correct. However, the data within each field has been swapped. If field aDescr.A was read with a little-endian word loading process, the data in memory would be 0x47464544, even though the original data was written as 0x44454647.