Embedded Systems

Additional software components In addition to the core operating system, many embedded systems have additional upper-layer software components. These components consist of networking protocol stacks like CAN, TCP/IP, FTP, HTTP, and HTTPS, and also included storage capabilities like FAT and flash memory management systems. If the embedded device has audio and video capabilities, then the appropriate drivers and codecs will be present in the system. In the case of the monolithic kernels, many of these software layers are included. In the RTOS category, the availability of the additional software components depends upon the commercial offering. Hardware Hardware includes the chips, wires, circuit boards, buttons and displays. CPUs The most important chip is the central processing unit or CPU. This runs the software instructions. It can be a standard microprocessor or a microcontroller. Microcontro...

Preemptive multitasking or multi-threading In this type of system, a low-level piece of code switches between tasks or threads based on a timer (connected to an interrupt). This is the level at which the system is generally considered to have an "operating system" kernel. Depending on how much functionality is required, it introduces more or less of the complexities of managing multiple tasks running conceptually in parallel. As any code can potentially damage the data of another task (except in larger systems using an MMU) programs must be carefully designed and tested, and access to shared data must be controlled by some synchronization strategy, such as message queues, semaphores or a non-blocking synchronization scheme. Because of these complexities, it is common for organizations to use a real-time operating system (RTOS), allowing the application programmers to concentrate on device functionality rather than operating system...

High vs low volume For high volume systems such as portable music players or mobile phones, minimizing cost is usually the primary design consideration. Engineers typically select hardware that is just “good enough” to implement the necessary functions. For low-volume or prototype embedded systems, general purpose computers may be adapted by limiting the programs or by replacing the operating system with a real-time operating system. There are several different types of software architecture in common use. Simple control loop In this design, the software simply has a loop. The loop calls subroutines, each of which manages a part of the hardware or software. Hence it is called a simple control loop or control loop. Interrupt-controlled system Some embedded systems are predominantly controlled by interrupts. This means that tasks performed by the system are triggered by different kinds of events; an interrupt could be gen...

Debugging Embedded debugging may be performed at different levels, depending on the facilities available. The different metrics that characterize the different forms of embedded debugging are: does it slow down the main application, how close is the debugged system or application to the actual system or application, how expressive are the triggers that I can set for debugging (e.g., I want to inspect the memory when a particular program counter value is reached), and what can I inspect in the debugging process (such as, only memory, or memory and registers, etc.). From simplest to most sophisticated they can be roughly grouped into the following areas: Interactive resident debugging, using the simple shell provided by the embedded operating system (e.g. Forth and Basic) External debugging using logging or serial port output to trace operation using either a monitor in flash or using a debug server like the Remedy Debugger which even...

ASIC and FPGA solutions A common array of n configuration for very-high-volume embedded systems is the system on a chip (SoC) which contains a complete system consisting of multiple processors, multipliers, caches and interfaces on a single chip. SoCs can be implemented as an application-specific integrated circuit (ASIC) or using a field-programmable gate array (FPGA). Peripherals Serial Communication Interfaces (SCI): RS-232, RS-422, RS-485, etc.Embedded systems talk with the outside world via peripherals, such as: Synchronous Serial Communication Interface: I2C, SPI, SSC and ESSI (Enhanced Synchronous Serial Interface) Universal Serial Bus (USB) Multi Media Cards (SD cards, Compact Flash, etc.) Networks: Ethernet, LonWorks, etc. Fieldbuses: CAN-Bus, LIN-Bus, PROFIBUS, etc. Timers: PLL(s), Capture/Compare and Time Processing Units Discrete I...

Processors in embedded systems Embedded processors can be broken into two broad categories. Ordinary microprocessors (μP) use separate integrated circuits for memory and peripherals. Microcontrollers (μC) have on-chip peripherals, thus reducing power consumption, size and cost. In contrast to the personal computer market, many different basic CPU architectures are used, since software is custom-developed for an application and is not a commodity product installed by the end user. Both Von Neumann as well as various degrees of Harvard architectures are used. RISC as well as non-RISC processors are found. Word lengths vary from 4-bit to 64-bits and beyond, although the most typical remain 8/16-bit. Most architectures come in a large number of different variants and shapes, many of which are also manufactured by several different companies. Numerous microcontrollers have been developed for embedded systems use. General-purpose microproc...