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ARM Processor Instruction Set Architectureask ARM

The ARM processor architecture provides support for the 32-bit ARM and 16-bit Thumb® Instruction Set Architectures (ISAs) along with architecture extensions to provide support for Java acceleration (Jazelle™), security (TrustZone™), Intelligent Energy Manager (IEM), SIMD, and NEONTM technologies.

The ARM ISA is constantly improving to meet the increasing demands of leading edge applications developers, while retaining the backwards compatibility necessary to protect investment in software development.

Architecture Diagram

The oldest version of the processor architecture supported today. All previous versions are now obsolete. Implementations include some members of the ARM7™ processor family and Intel StrongARM® processors. ARMv4 can be considered a 32-bit ISA operating in a 32-bit address space.

The ARMv4T processor architecture added the 16-bit Thumb® instruction set which enabled compilers to generate more compact code (memory savings of up to 35% over the equivalent 32-bit code), while retaining all the benefits of a 32-bit system.

In 1999, the ARMv5TE processor architecture introduced improvements to the Thumb architecture, along with ARM ‘Enhanced’ DSP (digital signal processing) instruction set extensions to the ARM ISA.

The Thumb changes added a few new instructions along with improvements to Thumb/ARM interworking, greatly improving compiler capabilities and the ability to mix and match ARM versus Thumb routines to balance code size and performance.

The enhanced DSP instructions include support for saturated arithmetic, and provide up to 70% performance improvement for audio DSP applications. Many systems require the flexibility of a microcontroller combined with the data-processing capability of a DSP, historically forcing designers to compromise performance with cost, or adopt complex multi processor strategies. The ‘E’ instruction set extensions were designed to provide a DSP capability in a general purpose CPU, resulting in improved performance and flexibility.

In 2000, the ARMv5TEJ processor architecture added the Jazelle® technology extension to support Java acceleration technology, which is particularly suited to small memory footprint designs. Jazelle technology’s acceleration of Java bytecodes provides significantly higher performance than a software-only based Java Virtual Machine (JVM), accelerating Java execution by 8x and providing an 80% reduction in power consumption compared to a non Java-accelerated core. This functionality gives platform developers increased freedom to run Java code alongside established operating systems (OS) and applications on an ARM processor.

The ARMv6 processor architecture, announced in 2001, features improvements in many areas covering the memory system, improved exception handling and better support for multiprocessing environments. ARMv6 also includes media instructions to support Single Instruction Multiple Data (SIMD) software execution. The SIMD extensions are optimized for a broad range of software applications including video and audio codecs, where the extensions increase performance by up to four times. In addition Thumb-2 and TrustZone® technologies were introduced as variants of the ARMv6 architecture. The first implementation of the ARMv6 architecture was the ARM1136J(F)-STM processor announced in Spring 2002, followed by the ARM1156T2(F)-STM and the ARM1176JZ(F)-STM processors in 2003.

The ARMv7 processor architecture lies below the CortexTM family of processors and defines three distinct processor profiles: the A profile for sophisticated, virtual memory-based OS and user applications; the R profile for real-time systems; and the M profile optimized for microcontroller and low-cost applications.

All ARMv7 architecture profiles implement Thumb® -2 technology which is built on the foundation of the ARM industry-leading Thumb code compression technology, while retaining complete code compatibility with existing ARM solutions. The ARMv7 architecture also includes the NEON™ technology extensions to increase DSP and media processing throughput by up to 400 percent, and offers improved floating point support to address the needs of next generation 3D graphics and games physics, as well as traditional embedded control applications.

NEON Media Acceleration Technology
ARM NEON technology is an architecture option with the ARMv7A architecture and is designed to address the demands of next generation high-performance, media intense, low power mobile handheld devices. NEON technology is a 64/128-bit hybrid SIMD architecture, developed by ARM to accelerate the performance of multimedia and signal processing applications including video encode/decode, 3D graphics, speech processing, compressed audio decoding, image processing, telephony and sound synthesis.

Vector Floating Point (VFP)
Vector Floating Point (VFP) coprocessor support is an architecture option. The VFP architecture supports single and double precision floating point arithmetic, and is fully IEEE 754 compliant with suitable software library support. The VFP architecture also includes a fully deterministic ‘Run fast Mode’.

Provision of a hardware floating point is essential for many applications, and can be used as part of a System on Chip (SoC) design flow using technical computing tools (eg MatLab® and MATRIXx®) to directly model the system and derive the application code. The vector processing capability of the ARM VFP can be used to increase performance of imaging applications such as scaling, 2D and 3D transforms, font generation, and digital filters.

ARM currently has VFP support for the ARM9™, ARM10™ and ARM11™ processor families:
 VFP9-S™ and VFP10™. Additional VFP options, VFPv3, were introduced with the ARMv7 architecture.

ARM TrustZone
The ARM TrustZone extensions provide hardware support for two separate address spaces, such that code executing in the non-secure world cannot gain access to any address space marked as secure. A new monitor mode supports transition between the two worlds.
The technology provides a secure environment for system features such as key management and/or authentication mechanisms enabled by an open OS. The protection provided by the technology is necessary for consumer privacy and extending a range of services, such as mobile banking and multimedia entertainment, to widespread consumer adoption and use.

Thumb-2 Technology
ARM and Thumb code each execute in their own processor state. Thumb-2 core technology adds a mixed mode capability, defining a new set of 32-bit instructions that execute alongside traditional 16-bit instructions in Thumb state. This reduces, or can remove, the need for balancing ARM and Thumb code in a system, providing ‘ARM levels of performance’ with ‘Thumb code density’.

Thumb-2 technology builds on the success of Thumb technology, adding to ARM’s strengths as the leading supplier of low power, high performance processors and systems, supply cost effective and timely solutions across a wide range of market segments.

Other Related Technologies
In addition to the above technologies, several other system technologies with their own architecture provisions are available from ARM.

Debug and Trace 
ARM's debug and trace tools enable system developers to quickly debug real-time software, and to trace instruction execution and associated program data at full core speed. The debug and trace offering includes host based tools along with components such as EmbeddedICE, Embedded Trace Macrocell (ETM™), and the latest CoreSight™ technology, which form part of a modern SoC.

The AMBA® protocol is an open standard, on-chip bus specification that details a strategy for the interconnection and management of functional blocks that makes up a System-on-Chip (SoC). It facilitates "right-first-time" development of embedded processors with one or more CPU/signal processors and multiple peripherals. The AMBA protocol enhances a reusable design methodology by defining a common backbone for SoC modules. 

ARM Intelligent Energy Manager
ARM Intelligent Energy Manager (IEMTM) technology implements advanced algorithms to optimally balance processor workload and energy consumption, while maximizing system responsiveness to meet end-user performance expectations. The Intelligent Energy Manager technology works with the OS and applications running on the mobile phone to dynamically adjust the required CPU performance level through a standard programmer's model.

See Also
 ARM Media Extensions>> 
 The Thumb Architecture Extension>> 
 ARM DSP Instruction Set Extensions>> 
 TrustZone Technology Overview>> 
 ARMv7 Architecture>> (698Kb .pdf) 
 ARM DSP-Enhanced Extensions>>
(94KB .pdf)
 ARM Architecture Version 6 (v6) White Paper>>
(87KB .pdf)
 Improving ARM Code Density and Performance>>
(36KB .pdf)


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