Exploring embedded systems

Every computer system created to solve a particular problem as part of a larger system or device is an embedded system. Even your general-purpose PC or laptop contains many embedded systems. A keyboard, a hard drive, a network card, or a Wi-Fi module—each of these is an embedded system with a processor, often called a microcontroller, and its own software, often called firmware.

Let's now dive into the different features of an embedded system.

How are they different from desktop or web applications?

The most distinctive feature of embedded systems compared to desktops or servers is their tight coupling of hardware and software specialized to accomplish a particular task.

Embedded devices work in a wide range of physical and environmental conditions. Most of them are not designed to work only in dedicated conditioned data centers or offices. They have to be functional in uncontrollable environments, often without any supervision and maintenance.

Since they are specialized, hardware requirements are precisely calculated to accomplish the task of being as cost-efficient as possible. As a result, the software aims to utilize 100% of the available resources with minimal or no reserves.

The hardware of embedded systems is much more differentiated compared to regular desktops and servers. The design of each system is individual. They may require very specific CPUs and schematics that connect them to memory and peripheral hardware.

Embedded systems are designed to communicate with peripheral hardware. A major part of an embedded program is checking the status, reading input, sending data, or controlling the external device. It is common for an embedded system to not have a user interface. This makes development, debugging, and diagnostics much more difficult compared to doing the same on traditional desktop or web applications.

Types of embedded systems

Embedded systems span a wide range of use cases and technologies—from powerful systems used for autonomous driving or large-scale storage systems to tiny microcontrollers used to control light bulbs or LED displays. 

Based on the level of integration and specialization of hardware, embedded systems can roughly be divided into the following categories:

• Microcontrollers (MCUs)
• A System on Chip (SoC)  
• Application-Specific Integrated Circuits (ASICs) 
• Field Programmable Gate Arrays (FPGAs)

Microcontrollers

MCUs are general-purpose integrated circuits designed for embedded applications. A single MCU chip typically contains one or more CPUs, memory, and programmable input/output peripherals. Their design allows them to interface directly with sensors or actuators without adding any additional components.

MCUs are widely used in automobile engine control systems, medical devices, remote controls, office machines, appliances, power tools, and toys.

Their CPUs vary from simple 8-bit processors to the more complex 32-bit and even 64-bit processors. 

Lots of MCUs exist; the most common ones nowadays are the following:

• The Intel MCS-51 or 8051 MCU.
• AVR by Atmel
• The Programmable Interface Controller (PIC) from Microchip Technology
• Various ARM-based MCUs

System on Chip

An SoC is an integrated circuit that combines all the electronic circuits and parts needed to solve a particular class of problem on a single chip.

It may contain digital, analog, or mixed-signal functions, depending on the application. The integration of most electronic parts in a single chip gives two major benefits: miniaturization and low power consumption. Compared to a less-integrated hardware design, an SoC requires significantly less power. The optimization of power consumption on the hardware and software levels allows it to create systems that can work for days, months, and even years on a battery without an external power source. Often, it also integrates radio frequency signal processing, which, along with its compact physical size, makes it an ideal solution for mobile applications. Besides that, SoCs are commonly used in the automotive industry, in wearable electronics, and in the Internet of Things (IoT):

Figure 1.1: A Raspberry Pi Model B+

A Raspberry Pi family of single-board computers is an example of a system based on the SoC design. Model B+ is built on top of a Broadcom BCM2837B0 SoC with an integrated quad-core 1.4 Hz ARM-based CPU, 1 GB memory, a network interface controller, and four Ethernet interfaces.

The board has four USB interfaces, a MicroSD card port to boot an operating system and store data, Ethernet and Wi-Fi network interfaces, HDMI video output, and a 40-pin GPIO header to connect custom peripheral hardware.

It is shipped with the Linux operating system and is an excellent choice for educational and DIY projects.

Application-specific integrated circuits

Application-specific integrated circuits, or ASICs, are integrated circuits customized by their manufactures for a particular use. The customization is an expensive process but allows them to meet the requirements that are often infeasible for solutions based on general-purpose hardware. For example, modern high-efficiency Bitcoin miners are usually built on top of specialized ASIC chips. 

To define the functionality of ASICs, hardware designers use one of the hardware description languages, such as Verilog or VHDL.

Field programmable gate arrays

Unlike SoCs, ASICs, and MCUs, field programmable gate arrays, or FPGAs, are semiconductor devices that can be reprogrammed on a hardware level after manufacturing. They are based around a matrix of configurable logic blocks (CLBs), which are connected via programmable interconnects. The interconnects can be programmed by developers to perform a specific function according to their requirements. The FPGA is programmed with a Hardware Definition Language (HDL). It allows the implementation of any combination of digital functions in order to process a massive amount of data very quickly and efficiently.