Central processing units, or CPUs, are used in the technology we use every day, from smartphones, to laptop computers, to wearables. These processors allow these devices to carry out instructions and tasks in order for it to perform its designated function. While there are different types of processors used in the devices used today, ARM processors have quickly become some of the most widely used, with up to billions of ARM-based devices produced each year. So, what exactly is an ARM processor and how does it differ from other processors used in embedded systems? In this article, we’ll provide background on the ARM processor, its comparison to other processor types, and some of its advantages and disadvantages.

What is a CPU?

CPUs are essentially the brains of an embedded system where it uses specific instructions, or an instruction set, to move data between registers and memory or to perform certain calculations as required. These days, most computing devices are likely to have either a processor using the x86 design, like Intel processors, or the ARM design used in Android/Apple smartphones or tablets. ARM CPUs are also being increasingly implemented into laptop computers as they continue to evolve.

Photo by Sergei Starostin from Pexels

Background of ARM Processors

ARM processors were first designed and introduced by ARM Holdings plc which was founded in 1990 by Acorn Computers, Apple, and VLSI Technology. Initially, ARM stood for Acorn RISC Machine but was later changed to Advanced RISC Machine. ARM Ltd develops the ARM architecture and licenses the IP to allow its licensees/partners/customers to subsequently build and sell the chip within their own designs/products, such as system-on-chip or system-on-modules designs. This is a different approach to other CPU manufacturers such as Intel or AMD that design and manufacture their own chips.

RISC vs CISC

As stated within its name, ARM processors are considered to be RISC based, or Reduced Instruction Set Computer. RISC machines are an alternative to CISC machines, or Complex Instruction Set Computer.

Unlike CISC-based processors, such as Intel x86 or AMD x86-64 microchips, which focus on reducing the number of instructions per program directly upon memory, RISC-based architecture focuses on reducing the complexity of instructions and executes them within a cycle at a high clock speed. This means that the same instruction executed on a CISC architecture might take several instructions to execute on a RISC machine.

In simpler terms, RISC emphasizes efficiency in cycles per instruction and CISC emphasizes efficiency in instructions per program, therefore RISC machines may be considered to be more efficient.

However, between CISC- and RISC-based CPU architecture, there is no processor that is considered to be superior in terms of design or function. Depending on the application, one may be better suited for certain uses.

Uses Cases: Mobile vs Laptop

ARM processors are commonly found in devices like mobiles phones while Intel processors are often used in larger devices like laptop or desktop computers. Because ARM is RISC based, the architecture requires fewer transistors which helps to improve cost, power consumption, and produces lower heat. Additionally, unlike computers which often prioritize performance, smartphones tend to benefit from the longer battery life and lower heat dissipation ARM provides. Also, ARM processors rely on software for performance while Intel processors rely on hardware. Again, as ARM processors evolve, they are being expanded into more and more applications, with computers being one.

What are the Advantages and Disadvantages of ARM Processors?

There are multiple advantages as to why device manufacturers would choose to implement ARM processors within their product.

Advantages

ARM processors are affordable to create and typically don’t require expensive equipment to do so. ARM processors are often ideal for lower cost devices such as mobile phones.

Due to its RISC design, which has a less complex architecture, ARM processors are simpler in design and are often much more compact. This allows the processors to be implemented in smaller devices. This is a benefit to the growing consumer demands for more handheld and portable devices.

ARM processors also operate using low power requirements and consume less power compared to other processors due to its RISC architecture design. This is also due to its ability to run only one cycle to execute a command, reducing functions.

Additionally, ARM processors consume less battery due to its single-cycle computing set; therefore, ARM processors have a better battery life. This is also often ideal for mobiles devices that are often used without a power connection, unlike laptop computers.

ARM processors also generate less heat, allowing devices like the smartphone or tablet to be thinner and be constantly held by the user.

Disadvantages

• ARM is not compatible with x86 programs like Windows OS.
• The speeds are limited in some processors.
• The simpler instruction set may be inadequate for heavier workloads.
• ARM has a limited calculation capacity.
• Performance depends on the ability of the programmer to execute properly and often require highly skilled programmers.

Testing and Development using ARM-based Devices

Total Phase offers various debugging and development tools that allow users to test their embedded system devices as well as monitor the bus for any errors or inconsistencies.

Our I2C and SPI host adapters allow users to emulate master or slave devices. Users can emulate a master device such as a CPU to test slave behavior or can be used as a slave device to test the validity of the master and its commands. Depending on the project requirements, Total Phase offers several host adapter options:

The Aardvark I2C/SPI Host Adapter is a general-purpose host adapter that can act as an I2C or SPI master or slave device, making it an easy and cost-effective way to prototype. It can support I2C master and slave speeds up to 800 kHz, SPI master speeds up to 8 MHz, and SPI slave speeds up to 4 MHz.

The Cheetah SPI Host Adapter is a high-speed SPI adapter that is capable of communicating over SPI at up to 40+ MHz. The Cheetah adapter is specifically designed to communicate with high-speed, SPI-based flash memory.

The Promira Serial Platform is our most advanced serial device that operates at higher-speeds, includes integrated level shifting, and offers more GPIO and slave select options compared to other host adapters. As an I2C master and slave, this device can support up to 3.4 MHz, and as an SPI master can support up to 80 MHz and up to 20 MHz as an SPI slave.

The Beagle I2C/SPI Protocol Analyzer allows users to gain insight into the I2C and SPI bus by displaying data exchanges, errors, and other pertinent bus information in real time. This tool can non-intrusively monitor I2C traffic up 4 MHz and SPI traffic up to 24 MHz.

These tools are interfaced through a host computer using software that is supported on Windows, Mac, and Linux machines. We also offer royalty-free APIs so users can use these devises in various environments. Along with Windows, Mac, and Linux APIs, Total Phase offers ARM APIs for our products that allow users to interface our tools on ARM machines, including the popular Raspberry Pi.

To learn how to interface with one of our tools using the ARM API please see our video:

Interfacing with the Aardvark I2C/SPI Host Adapter Using a Raspberry Pi ARM System

For any additional questions on how our tools can support your own projects, please email at us sales@totalphase.com.