What is Thumb code?

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. Thumb, therefore, makes the ARM7TDMI core ideally suited to embedded applications with restricted memory bandwidth, where code density and footprint is important.

What is Thumb programming model?

The Thumb instruction set is a subset of the ARM instruction set, re-encoded to 16 bits. It supports higher code density and systems with memory data buses that are 16 bits wide or narrower. Thumb-2 is a major enhancement to the Thumb Instruction Set Architecture (ISA).

What are Thumb-2 instructions?

Thumb-2 is a superset of the Thumb instruction set. Thumb-2 introduces 32-bit instructions that are intermixed with the 16-bit instructions. The Thumb-2 instruction set covers almost all the functionality of the ARM instruction set. Thumb-2 is backwards compatible with the ARMv6 Thumb instruction set.

What is Thumb architecture?

Thumb-2 is an enhancement to the 16-bit Thumb Instruction Set Architecture (ISA). It adds 32-bit instructions that can be freely intermixed with 16-bit instructions in a program. The additional 32-bit instructions enable Thumb-2 to cover the functionality of the ARM instruction set.

Why Thumb instruction set is called Thumb?

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.

Where and why is Thumb mode used?

Thumb mode allows for code to be smaller, and can potentially be faster if the target has slow memory.

How do I switch to Thumb 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.

How do I switch from Thumb to ARM mode?

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 the purpose of the Thumb instruction set?

The Thumb instruction set provides most of the functionality required in a typical application. Arithmetic and logical operations, load/store data movements, and conditional and unconditional branches are supported.

What is the difference between ARM and Thumb mode?

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. The Thumb instruction set provides better code density, at the expense of performance.

Which instruction can be used to jump to Thumb code from ARM state?

These directives do not change the instruction set state of the processor. To do this, you must use an appropriate instruction, for example BX or BLX to change between ARM and Thumb states when performing a branch.

Is the Thumb instruction set the same as arm?

Before the introduction of 32-bit Thumb instructions, the Thumb instruction set was limited to a restricted subset of the functionality of the ARM instruction set. Almost all Thumb instructions were 16-bit. Together, the 32-bit and 16-bit Thumb instructions provide functionality that is almost identical to that of the ARM instruction set.

Can a 32 bit instruction be executed on a thumb?

Every Thumb instruction could instead be executed via the equivalent 32-bit ARM instruction. However, not all ARM instructions are available in the Thumb subset; for example, there’s no way to access status or coprocessor registers.

Are there 16 bit or 32 bit ARM instruction sets?

The availability of both 16-bit Thumb and 32-bit ARM instruction sets gives designers the flexibility to emphasize performance or code size on a subroutine level, according to the requirements of their applications.

How big is Thumb code compared to ARM code?

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. Thumb, therefore, makes the ARM7TDMI core ideally suited to embedded applications with restricted memory bandwidth, where code density and footprint is important.