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Figure 6.5 ARM Endian Support— Word Load/Store with E- Bit
endian support A state bit ( E- bit) in the system control register is set and cleared under program control
using the SETEND instruction. The E- bit defines which endian to load and store data. Figure 12.5 illustrates
the functionality associated with the E- bit for a word load or store operation. This mechanism enables
efficient dynamic data load/store for system designers who know they need to access data structures in
the opposite endianness to their OS/environment. Note that the address of each data byte is fixed in
memory. However, the byte lane in a register is different.

6.5 ADDRESSING MODES
The address field or fields in a typical instruction format are relatively small. We would like to be able to
reference a large range of locations in main memory or, for some systems, virtual memory. To achieve
this objective, a variety of addressing techniques has been employed. They all involve some trade- off
between address range and/or addressing flexibility, on the one hand, and the number of memory
references in the instruction and/or the complexity of address calculation, on the other. In this section,
we examine the most common addressing techniques, or modes:

■ Immediate

■ Direct

■ Indirect
■ Register

■ Register indirect

■ Displacement

■ Stack

These modes are illustrated in Figure 13.1. In this section, we use the following notation: A = contents of
an address field in the instruction R = contents of an address field in the instruction that refers to a register

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