Embedded software is computersoftware, written to control machines or devices that are not typically thought of as computers, commonly known asembedded systems. It is typically specialized for the particularhardware that it runs on and has time and memory constraints.[1] This term is sometimes used interchangeably withfirmware.[2]
A precise and stable characteristic feature is that no or not all functions of embedded software are initiated/controlled via a humaninterface, but through machine-interfaces instead.[3]
Manufacturers build embedded software into the electronics ofcars, telephones, modems,robots, appliances, toys, security systems,pacemakers, televisions and set-top boxes, anddigital watches, for example.[4] This software can be very simple, such as lighting controls running on an8-bitmicrocontroller with a fewkilobytes of memory with the suitable level of processing complexity determined with a Probably Approximately Correct Computation framework[5] (a methodology based onrandomized algorithms). However, embedded software can become very sophisticated in applications such asrouters, optical network elements,airplanes,missiles, andprocess control systems.[6]
Unlike standard computers that generally use an operating systems such asmacOS,Windows orLinux, embedded software may use no operating system. When they do use one, a wide variety of operating systems can be chosen from, typically areal-time operating system. Code for embedded software is typically written inC orC++, but varioushigh-level programming languages, such asJava,Python andJavaScript, are now also in common use to target microcontrollers and embedded systems.[7]Assembly languages are often used too, especially in booting andinterrupt handling.Ada is used in some military and aviation projects.
Most consumers are familiar withapplication software that provide functionality on a computer. However embedded software is often less visible, but no less complicated. Unlike application software, embedded software has fixed hardware requirements and capabilities, and addition of third-party hardware or software is strictly controlled.
Embedded software needs to include all neededdevice drivers at manufacturing time, and the device drivers are written for the various hardware devices. These device drivers, called BSP (Board support package), form the layer of software containing hardware-specific drivers and other routines that allow a particular operating system (traditionally a real-time operating system, or RTOS) to function in a particular hardware environment (a computer or CPU card), integrated with the RTOS itself. The software is highly dependent on the CPU and specific chips chosen. Most embedded software engineers have at least a passing knowledge of readingschematics, and reading data sheets for components to determine usage of registers and communication system. Conversion betweendecimal,hexadecimal andbinary is useful as well as usingbit manipulation.[8]
Web applications are often used for managing hardware, although XML files and other output may be passed to a computer for display. File systems with folders are typically used, however SQL databases are often absent.
Software development requires use of across compiler, which runs on a computer but produces executable code for the target device. Debugging requires use of anin-circuit emulator, and debugging hardware such asJTAG orSWD debuggers. Software developers often have access to the complete kernel (OS) source code.
Size of the storage memory and RAM can vary significantly. Some systems run in 16 KB of Flash and 4 KB of RAM with a CPU operating at 8 MHz, other systems can rival contemporary computers.[9] These space requirements lead to more work being done in C orembedded C++, instead of C++. Interpreted languages likeBASIC (while e.g.Parallax Propeller can use compiled BASIC) andJava (Java ME Embedded 8.3[10] is available for e.g.ARM Cortex-M4,Cortex-M7 microcontrollers and olderARM11 used inRaspberry Pi andIntel Galileo Gen. 2) are not commonly used; while an implementation of the interpretedPython 3 language – MicroPython – is however available expressly for microcontroller use, e.g.32-bitARM-based (such as BBCmicro:bit) and16-bitPIC microcontrollers.
Communications between processors and between one processor and other components are essential. Besidesdirect memory addressing, hardware level common protocols includeI²C,SPI,serial ports,1-Wires,Ethernets, andUSB.
Communications protocols designed for use inembedded systems are available asclosed source from companies including InterNiche Technologies andCMX Systems.Open-source protocols stem fromuIP,lwip, and others.