Cortex-A8 R2P2.pdf - ARM Information Center

Programmer’s Model2.3 ThumbEE instruction setThumbEE is a variant of the Thumb-2 instruction set. It is designed as a target fordynamically generated code. This is code compiled on the device either shortly beforeor during execution from a portable bytecode or other intermediate or nativerepresentation. It is particularly suited to languages that employ managed pointers orarray types. ThumbEE provides increased code density for the compiled binarycompared with the compiled code for the ARM or Thumb-2 instruction set. ThumbEEintroduces a new processor state, the ThumbEE state, indicated by both the T bit and theJ bit in the CPSR Register being set to 1.See the ARM Architecture Reference Manual for information on the ARM, Thumb, andThumbEE instruction sets.2.3.1 InstructionsIn ThumbEE state, the processor uses almost the same instruction set as Thumb-2although some instructions behave differently, and a few are removed, or added.The key differences are:• additional state changing instructions in both Thumb state and ThumbEE state• new instructions to branch to handlers• null pointer checking on loads and stores• an additional instruction in ThumbEE state to check array bounds• some other modifications to the load, store, and branch instructions.ThumbEE instructions are accessible when the processor is in ThumbEE state.2.3.2 ConfigurationTwo registers provide ThumbEE configuration:• ThumbEE Configuration Register. This contains a single bit, the ThumbEEconfiguration control bit, XED.• ThumbEE HandlerBase Register. This contains the base address for ThumbEEhandlers.A handler is a short, commonly executed, sequence of instructions. It is typically,but not always, associated directly with one or more bytecodes or otherintermediate language elements.2-6 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E