Page 40 - ARM Based Microcontroller Projects Using MBED

26 3. THE ARM MICROCONTROLLERS

In this venture, Apple invested by providing the cash, VLSI provided the necessary technol-
ogy tools, and Acorn provided the experienced design engineers. By the year ARM became a
£26.6 million company with net income of £2.9 million. In 1998 ARM, currently called ARM
Holdings, was listed on the London Stock Exchange and NASDAQ. In later years ARM
designed new processor architectures and sold the intellectual property rights as licenses
to the firms who wished to incorporate ARM designs in their own products. In 2016 SoftBank
bought ARM for $31 billion.
ARM has been designing 32-bit processors for over 20 years and in the last few years they
have also started to offer 64-bit designs. In actual fact ARM is a company specialized in de-
signing the processor architecture and they do not manufacture or sell processor chips. ARM
makes money by licensing their designs to chip manufacturers. The manufacturers use the
core ARM processors (e.g., the core CPU) and integrate with their own peripherals to end
up in a complete microcontroller chip. ARM is then given royalty fees for each chip
manufactured by the third-party companies. Companies that use ARM core processors in-
clude Apple, Atmel, Broadcom, Cypress Semiconductors, Freescale Semiconductors, Analog
Devices, Nvidia, NXP, Samsung Electronics, Texas Instruments, Qualcomm, Renesas, and
many others.
The ARM concept became so popular that in mobile applications in 2005, about 98% of all
mobile phones sold used at least one ARM processor. In 2011, the 32-bit ARM architecture
was the most widely used and most popular architecture used in mobile devices. Over 10 bil-
lion units were produces in 2013. The ARM architecture is known to offer the best MIPS to
Watts ratio as well as MIPS to $ ratio in the industry, and the smallest CPU size.
Many ARM cores have been designed over the years, such as the ARMv1, ARMv2, …,
ARMv8 and so on, ranging from 32-bits to 64-bits. The 32-bit ARMv7-A was the most widely
used architecture in mobile devices in 2011. This includes architectures such as Cortex-A5,
Cortex-A7, Cortex-A8, and so on. Lower performing cores have lower license fees than higher
performing cores. The ARMv6-M and ARMv7E-M are used in lower performance
microcontroller-based control and monitoring applications and these architectures include
Cortex-M0, Cortex-M0+, Cortex-M1, Cortex-M3, Cortex-M4, and Cortex-M7.

3.3 THE ARM PROCESSOR ARCHITECTURE

3.3.1 CICS and RISC
Basically there are two types computer designs as far as the CPU design is considered:
Complex Instruction Set Computer (CISC) and RISC. Traditionally all CPU designs were based
on CISC where the instruction set of these computers had many instructions. Many micropro-
cessors, including the 6502 were based on CISC where some instructions were executed in one
cycle and some others required several processor cycles to execute.
Most present day CPUs have limited instructions in their instructions sets and are therefore
called RISC. ARM processors use RISC-based designs and this is one of the reasons that they
are used widely, especially in mobile devices. Because of simpler designs the RISC processors
use less number of transistors and therefore reduced power consumption. These processors
execute one instruction per cycle and as a result these CPUs are fast, but they may need to