The ARM processor core is a leading processor design for the embedded domain. In the embedded domain, both memory and energy are important concerns. For this reason the 32 bit ARM processor also supports the 16 bit Thumb instruction set. For a given program, typically the Thumb code is smaller than the ARM code. Therefore by using Thumb code the I-cache activity, and hence the energy consumed by the I-cache, can be reduced. However, the limitations of the Thumb instruction set, in comparison to the ARM instruction set, can often lead to generation of poorer quality code. Thus, while Thumb code may be smaller than ARM code, it may perform poorly and thus may not lead to overall energy savings.
['Arvind Krishnaswamy', 'Rajiv Gupta']
Profile guided selection of ARM and thumb instructions