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What features does ARM provide?

British multinational semiconductor and software design company, ARM Holdings plc, offers complete solutions that are essential for the manufacturing process, but the company does not manufacture ICs. Moreover, it provides software development tools under the brand Keil and RealView. It also provides ARM architecture licensing for the companies that want to manufacture ARM-based CPUs or ‘system-on-chip’ products.

The ARM architecture is a simple hardware design allowing things to be left off the chip. It helps in creating small die-sized chip which helps in considerably reducing the cost. Its low cost, simple pipeline construction and the freedom to put the design point where the designer finds it suitable for low-power consumption adds onto the benefits it provides for embedded applications.

Fig. 1: Format of the CPSR and the SPSR (source: ARM reference manual)
Fig. 1: Format of the CPSR and the SPSR (source: ARM reference manual)

ARM allows an instruction set called ‘Thumb’, which compresses 32-bit instructions to 16 bits, enabling programs to be coded much more densely than standard RISC instruction sets. Processors enabled to execute ‘Thumb’ also allow 32-bit instructions to run on the same hence allowing 16-bit and 32-bit instructions to mix together without affecting the performance, maintaining powerful computing capabilities.

Fig. 2: General registers and program counter modes (source: http://aelmahmoudy.users.sourceforge.net/electronix /arm/chapter3.htm)
Fig. 2: General registers and program counter modes (source: http://aelmahmoudy.users.sourceforge.net/electronix
/arm/chapter3.htm)

ARM designs and licences intellectual property (IP) instead of manufacturing the chips. Two types of licences that ARM provides are ‘implementation licence’ and ‘architecture licence.’ Implementation licence provides information to design integrated circuit containing the ARM core. The architecture licence enables the licencees to design their own processor with ARM instruction set architecture.

ARM cores are simple compared to other processors since it can be manufactured with few transistors. ARM is a 32-bit instruction set architecture. Today, many embedded applications like smartphones, set-top boxes, digital televisions and digital cameras use an ARM processor due to their cost-effectiveness and low-power consumption. ARM architecture is compatible with all four major operating systems, i.e., Symbian OS, Palm OS, Windows and Android OS.

Fig. 3: An optimised ARM smartphone block diagram
Fig. 3: An optimised ARM smartphone block diagram

The instruction sets in ARM processor are classified as ARM instruction set, Thumb instruction set and Jazelle mode. ARM mode is a standard 32-bit instruction set. Thumb instruction set is a 16-bit compressed form that provides better performance than complex instruction set computers (CISCs). Jazelle DBX (direct bytecode eXecution) allows some ARM processor to execute Java bytecode.

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