Microprocessors designed for embedded systems offer limited processing power and features compared to the processors for computers. Microprocessors can be divided in to two types; RISC (Reduced instruction set computing) and, the opposite of it, CISC (Complex instruction set computing). Microprocessors for embedded systems are based on RISC mostly because RISC chips require far fewer transistors to perform the core logic compared to the CISC architecture. Smaller circuitry results in lesser area and energy consumption and this is the reason for the popularity and domination of RISC microprocessors in mobile and embedded devices market. Some of the top microprocessor families for embedded systems will be discussed here.
ARM (Advanced RISC Machine) is the most popular family of microprocessors in embedded systems market, based on the RISC instruction set architecture. Approximately 90% of all embedded 32-bit RISC processors belongs to the ARM family. Widely used ARM processor families are the ARM7, ARM9, ARM11 and Cortex, with ARM7TDMI being the most popular. The heart of Apple products, the A4 and A5 processors are also based on the ARM core. ARM family is basically 32-bit but there is also one other ARM architecture, known as Thumb, which supports 16-bit instructions. ARM microprocessors can perform multiple operations simultaneously due to the usage of multi stage pipelining and thus improving the processing speed. ARM microprocessors also offer rapid context switching as they have separate register banks for each mode of operation.
Texas Instruments bases many of their System on Chips on ARM architecture: OMAP4460, AM3517, DM3730, AM3703, AM3505. All the chips are based on ARM Cortex A-8, expect for the OMAP4460, which is designed over ARM Cortex A-9.
Another widely used RISC based embedded processor family is the PowerPC which was created jointly by IBM, Motorola and Apple. PowerPC architecture is an open standard and is based on IBM’s earlier POWER architecture. PowerPC family was actually designed for desktop computers and had been used considerably in Apple Macintosh computers, but they have also achieved popularity in embedded systems market. This is evident by the division of operating systems supported on PowerPC that some of them work on PowerPC based desktop computers and some work on PowerPC based embedded systems.
MIPS, formerly an acronym for Microprocessor without Interlocked Pipeline Stages, is also a RISC based 32- & 64-bit microprocessor family for embedded systems. MIPS is one of the first RISC architecture based processor families. It is not that famous as the ARM and PowerPC families but still has a good presence in networking equipments market like routers and residential gateways. Embedded MIPS processors have very low power consumption. MIPS I, MIPS II, MIPS III, MIPS IV, MIPS V, MIPS32, and MIPS64, all are instruction sets for MIPS family.
The AM3505 of Texas Instruments (TI) is a sister microprocessor of AM3517, both belonging to the Sitara family of ARM core based microprocessor units (MPU’s). Both AM3505 and AM3517 are similar except for the absence of an OpenGL graphics engine subsystem in AM3505 which is used for 3D graphics acceleration suitable for gaming applications. AM3505 and AM3517 were released by TI primarily to target industrial applications but both have also found good use in average consumer applications as well ranging from personal handheld multimedia & data management gadgets like smartphones, to large scale home & commercial automation solutions.
With power consumption of less than 1 milli Watt, AM3505 can be used in battery powered portable products. Like the AM3517, AM3505 is also based on the ARM Cortex A8 core which offers a considerable performance advantage over the ARM9 core which is used in other Sitara family MPU’s. This microprocessor is architecturally similar to the OMAP35xx application processors from TI except of the absence of a digital signal processor (DSP) module for HD (high definition) quality video processing. Despite the absence of a DSP, it is capable of processing HD video signals but with limited functionality. As mentioned above, 3D graphics processing module is also absent in this microprocessor, hence unable to produce same quality effects and visuals as possible through AM3517. Apart from this, AM3505 offers many other video related processing features like multiple concurrent image manipulation which is commonly known as “picture in picture”. Although it may be a disadvantage for not providing a DSP and the graphics accelerator subsystem, it is affects the cost reduction of chip which is further decreased by the usage of DDR2 memory in this MPU. This might trade off this disadvantage in the eyes of some electrical engineers.
Due to its target market, AM 3505 comes with industry focused connectivity features like PHY (physical layer) functionality in USB On The Go (OTG), dual USB host, an advanced CAN controller and EMAC. Major requirements for devices with industry targeted applications are the ruggedness and endurance against temperature and mechanical extremes of an industrial environment, to which it complies. AM3505 has usage mostly in applications requiring video displays because of the presence of its vast array of video signal capture and output features, making it an appropriate choice for embedded systems requiring a HMI (Human Machine Interface) or information and entertainment video output. AM3505 offers lots of peripherals and connectivity interfaces some of which include different types of timers, multiple serial ports, interfaces for removable storage media like SD card, 186 general purpose input output (GPIO) pins for customized application circuitry, JTAG test interface, etc. All major high level and real time operating systems like Linux, Windows Embedded & CE and Android, are supported by the AM3505.