What is thumb mode in ARM processor?
About ARM and Thumb Mode ARM instructions are 32 bits wide, and Thumb instructions are 16 wide. Thumb mode allows for code to be smaller, and can potentially be faster if the target has slow memory. Please consult documentation from your MCU vendor, or documentation from ARM, for additional information.
How do I switch from thumb to ARM mode?
To change between ARM and Thumb states, you must switch the assembler mode to produce the correct opcodes using ARM or THUMB directives. To generate ThumbEE code, use THUMBX . Assembler code using CODE32 and CODE16 can still be assembled by the assembler, but you are recommended to use ARM and THUMB for new code.
What is thumb in assembly language?
The THUMB directive instructs the assembler to interpret subsequent instructions as Thumb instructions, using the UAL syntax.
Is your thumb or ARM faster?
Thumb is not half as efficient as ARM, it is more like 10-15% more instructions to do the same thing as ARM.
What is the difference between Thumb and thumb2?
Thumb-2 is an enhancement to the 16-bit Thumb instruction set. The most important difference between the Thumb-2 instruction set and the ARM instruction set is that most 32-bit Thumb instructions are unconditional, whereas most ARM instructions can be conditional.
What is Thumb mode operation?
The Thumb instruction set consists of 16-bit instructions that act as a compact shorthand for a subset of the 32-bit instructions of the standard ARM. When it’s operating in the Thumb state , the processor simply expands the smaller shorthand instructions fetched from memory into their 32-bit equivalents.
What is the use of Cpsr?
The Linux/ARM embedded platform ARM v6/v7 maintains a status register called the CPSR (current program status register) that holds four status bits, negative (N), zero (Z), carry (C), and overflow (O). These bits can be used for conditional execution of subsequent instructions.
What is BLX instruction?
The BLX instruction copies the address of the next instruction into LR ( R14 , the link register). The BLX instruction can change the instruction set. BLX label always changes the instruction set. It changes a processor in ARM state to Thumb state, or a processor in Thumb state to ARM state.
What is thumb mode operation?
What is ARM instruction set and Thumb instruction set?
2.2 ARM, Thumb, and ThumbEE instruction sets ARM instructions are 32 bits wide. Thumb instructions are 16 or 32-bits wide. The ARM instruction set is a set of 32-bit instructions providing a comprehensive range of operations. ARMv4T and later define a 16-bit instruction set called Thumb.
Why do people have Thumb arms?
Thumb therefore offers a long branch range, powerful arithmetic operations, and a large address space. Thumb code is typically 65% of the size of ARM code, and provides 160% of the performance of ARM code when running from a 16-bit memory system.
What are the advantages of Thumb instruction set?
Summary of the Thumb Advantage Excellent code density The Thumb instruction set gives excellent code density compared to both 32-bit cores and the 8 and 16-bit processors commonly used in embedded applications. Memory size and system costs are thereby reduced.
