ARM MICROCONTROLLER

The ARM is a 32-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by ARM Limited. It was known as the Advanced RISC Machine, and before that as the Acorn RISC Machine. The ARM architecture is the most widely used 32-bit ISA in terms of numbers produced.[1][2] They were originally conceived as a processor for desktop personal computers by Acorn Computers, a market now dominated by the x86 family used by IBM PC compatible computers. But the relative simplicity of ARM processors made them suitable for low power applications. This has made them dominant in the mobile and embedded electronics market as relatively low cost and small microprocessors and microcontrollers.
As of 2007, about 98 percent of the more than a billion mobile phones sold each year use at least one ARM processor.[3] As of 2009, ARM processors account for approximately 90% of all embedded 32-bit RISC processors. ARM processors are used extensively in consumer electronics, including PDAs, mobile phones, iPods and other digital media and music players, hand-held game consoles, calculators and computer peripherals such as hard drives and routers.
The ARM architecture is licensable. Companies that are currently or formerly ARM licensees include Alcatel, Atmel, Broadcom, Cirrus Logic, Digital Equipment Corporation, Freescale, Intel (through DEC), LG, Marvell Technology Group, NEC, NVIDIA, NXP (previously Philips), Oki, Qualcomm, Samsung, Sharp, ST Microelectronics, Symbios Logic, Texas Instruments, VLSI Technology, Yamaha and ZiiLABS.
ARM processors are developed by ARM and by ARM licensees. Prominent examples of ARM Limited ARM processor families include the ARM7, ARM9, ARM11 and Cortex. Examples of ARM processors developed by major licensees include the DEC StrongARM, Freescale's i.MX, Marvell (formerly Intel) XScale, NVIDIA's Tegra, ST-Ericsson Nomadik, and Qualcomm's Snapdragon.

fter achieving some success with the BBC Micro computer, Acorn Computers Ltd considered how to move on from the relatively simple MOS Technology 6502 processor to address business markets like the one that would soon be dominated by the IBM PC, launched in 1981. The Acorn Business Computer (ABC) plan required a number of second processors to be made to work with the BBC Micro platform, but processors such as the Motorola 68000 and National Semiconductor 32016 were unsuitable, and the 6502 was not powerful enough for a graphics based user interface.
Acorn would need a new architecture, having tested all of the available processors and found them wanting. Acorn then seriously considered designing its own processor, and their engineers came across papers on the Berkeley RISC project. They felt it showed that if a class of graduate students could create a competitive 32-bit processor, then Acorn would have no problem. A trip to the Western Design Center in Phoenix showed Acorn engineers Steve Furber and Sophie Wilson that they did not need massive resources and state-of-the-art R&D facilities.
Wilson set about developing the instruction set, writing a simulation of the processor in BBC Basic that ran on a BBC Micro with a 6502 second processor. It convinced the Acorn engineers that they were on the right track. Before they could go any further, however, they would need more resources. It was time for Wilson to approach Acorn's CEO, Hermann Hauser, and explain what was afoot. Once the go-ahead had been given, a small team was put together to implement Wilson's model in hardware.
he official Acorn RISC Machine project started in October 1983. VLSI Technology, Inc were chosen as silicon partner, since they already supplied Acorn with ROMs and some custom chips. The design was led by Wilson and Furber, with a key design goal of achieving low-latency input/output (interrupt) handling like the MOS Technology 6502 used in Acorn's existing computer designs. The 6502's memory access architecture had allowed developers to produce fast machines without the use of costly direct memory access hardware. VLSI produced the first ARM silicon on 26 April 1985 – it worked first time and came to be known as ARM1 by April 1985.[4] The first "real" production systems named ARM2 were available the following year.
Its first practical application was as a second processor to the BBC Micro, where it was used to develop the simulation software to finish work on the support chips (VIDC, IOC, MEMC) and to speed up the operation of the CAD software used in developing ARM2. Wilson subsequently coded BBC Basic in ARM assembly language, and the in-depth knowledge obtained from designing the instruction set allowed the code to be very dense, making ARM BBC Basic an extremely good test for any ARM emulator. The original aim of a principally ARM-based computer was achieved in 1987 with the release of the Acorn Archimedes.
Such was the secrecy surrounding the ARM CPU project that when Olivetti were negotiating to take a controlling share of Acorn in 1985, they were not told about the development team until after the negotiations had been finalised. In 1992 Acorn once more won the Queen's Award for Technology for the ARM.
The ARM2 featured a 32-bit data bus, a 26-bit (64 Mbyte) address space and sixteen 32-bit registers. Program code had to lie within the first 64 Mbyte of the memory, as the program counter was limited to 26 bits because the top 6 bits of the 32-bit register served as status flags. The ARM2 was possibly the simplest useful 32-bit microprocessor in the world, with only 30,000 transistors (compare with Motorola's six-year older 68000 model with around 70,000 transistors). Much of this simplicity comes from not having microcode (which represents about one-quarter to one-third of the 68000) and, like most CPUs of the day, not including any cache. This simplicity led to its low power usage, while performing better than the Intel 80286.[5] A successor, ARM3, was produced with a 4KB cache, which further improved performance.
In the late 1980s Apple Computer and VLSI Technology started working with Acorn on newer versions of the ARM core. The work was so important that Acorn spun off the design team in 1990 into a new company called Advanced RISC Machines Ltd. For this reason, ARM is sometimes expanded as Advanced RISC Machine instead of Acorn RISC Machine. Advanced RISC Machines became ARM Ltd when its parent company, ARM Holdings plc, floated on the London Stock Exchange and NASDAQ in 1998.[6]
The new Apple-ARM work would eventually turn into the ARM6, first released in early 1992. Apple used the ARM6-based ARM 610 as the basis for their Apple Newton PDA. In 1994, Acorn used the ARM 610 as the main CPU in their Risc PC computers. DEC licensed the ARM6 architecture (which caused some confusion because they also produced Alpha microprocessors)[citation needed] and produced the StrongARM. At 233 MHz this CPU drew only 1 watt of power (more recent versions draw far less). This work was later passed to Intel as a part of a lawsuit settlement, and Intel took the opportunity to supplement their aging i960 line with the StrongARM. Intel later developed its own high performance implementation known as XScale which it has since sold to Marvell.
The ARM core has remained largely the same size throughout these changes. ARM2 had 30,000 transistors, while the ARM6 grew to only 35,000. ARM's business has always been to sell IP cores, which licensees use to create microcontrollers and CPUs based on this core. The most successful implementation has been the ARM7TDMI with hundreds of millions sold in almost every kind of microcontroller equipped device.[citation needed] The idea is that the Original Design Manufacturer combines the ARM core with a number of optional parts to produce a complete CPU, one that can be built on old semiconductor fabs and still deliver substantial performance at a low cost. Atmel Corp. has been a precursor design center in the ARM7TDMI-Based Embedded System.
ARM licensed about 1.6 billion cores in 2005. In 2005, about 1 billion ARM cores went into mobile phones.[7] As of January 2008, over 10 billion ARM cores have been built, and iSuppli predicts that 5 billion a year will ship in 2011.[8]
The common architecture supported on smartphones, personal digital assistants and other handheld devices is ARMv4. XScale and ARM926 processors are ARMv5TE, and are now more numerous in high-end devices than the StrongARM, ARM925T and ARM7TDMI based ARMv4 processors.
In 2009, some manufacturers introduced netbooks based on ARM architecture CPUs, in direct competition with netbooks based on Intel Atom.[9]