Embedded Systems

What is an embedded system?

Characteristics of an embedded system

  • Contains a processing engine, such as a general-purpose microprocessor.

  • Typically designed for a specific application or purpose.

  • Includes a single (or no) user interface.

  • Often is resource-limited. For example, it might have a small memory footprint and no hard drive.

  • Might have power limitations, such as requirements to operate from batteries.

  • Not typically used as a general-purpose computing platform.

  • General has application software built in, not user-selected.

  • Ships with all intended application hardware and software pre-integrated.

  • Often is intended for applications without human intervention.

What is a microcontroller, microprocessor, SoC, and SoM?

  • Microprocessor

  • Microcontroller

  • SoC (System on Chip)

  • SoM (System on Module)

Basic processor architecture

The ones most often found in embedded devices are Arm, MIPS, PowerPC, RISC-V, and x86, each in 32 and 64-bit variants, all with memory management units (MMU).

Bootloaders

A bootloader is a program in charge of initializing critical computer resources, such as program memory, and loading the OS into the memory. It serves as a bridge between the firmware and the operating system, ensuring th system is properly configured to begin execution of higher-level software.

How does the bootloader loads the OS/Program?

  1. Power-On / Reset: after the system is powered on or reset, the processor starts executing code from a predefined memory location, usually set by the hardware.

  2. Execution of bootloader: the firmware locates and hands over control to the bootloader, typically residing in non-volatile storage (e.g., flash memory or ROM).

  3. Hardware initialization: the bootloader initializes critical hardware, including memory controllers, I/O devices, and other peripherals.

  4. Operating system image location: the bootloader locates the operating system image, which could be stored in local storage (HDD, SSD, eMMC) or a remote server (via network boot).

  5. OS loading: the bootloader loads the OS image into RAM, preparing it for execution.

  6. Control handover: the bootloader passes control to the OS kernel, along with necessary system configuration data.

Types of bootloaders:

  • Stage-1 Bootloader: A minimal bootloader that loads a more complex Stage-2 bootloader. Commonly used in multi-stage boot processes.

  • Stage-2 Bootloader: A more feature-complete bootloader that initializes more hardware and loads the operating system. Examples include GRUB or LILO.

  • Primary Bootloader: Resides in the first sector of the boot device (e.g., MBR) and initiates the OS loading process.

  • Secondary Bootloader: Used in systems requiring additional steps to load the OS, often containing more advanced capabilities.

  • Network Bootloader: Supports booting the system over a network using protocols like PXE (Preboot Execution Environment).

Examples:

  • GRUB (GNU GRUB): A widely used bootloader for Linux and other operating systems.

  • LILO (Linux Loader): An older Linux bootloader, now largely replaced by GRUB.

  • UEFI Boot Manager: Used in systems with Unified Extensible Firmware Interface.

  • U-Boot: A versatile bootloader for embedded systems.

  • Windows Boot Manager: The default bootloader for Microsoft Windows operating systems.

Tasks of a bootloader:

  • Initialize Critical Hardware: Configure SDRAM controller, I/O controllers, graphics controllers, and other essential components.

  • Prepare System Memory: Initialize and map system memory to prepare for OS loading.

  • Allocate Resources: Manage resources like memory and interrupt circuits for peripheral devices.

  • Locate OS Image: Find the operating system image in storage or over a network.

  • Load OS Kernel: Load the OS kernel and pass control to it, along with essential configuration data such as:

    • Total memory size
    • Processor clock rates
    • Peripheral configuration (e.g., serial port settings)

Bare metal programming

Infinite for loop.

OS and RTOS concepts

Difference between an OS and RTOS:

  • OS (Operating System)

  • RTOS (Real-Time Operating System)

Examples: FreeRTOS, QNX, VxWorks What is DMA?

Direct Memory Acess

Timers

Time-Based - Hardware timers are key components of most microcontrollers. In addition to measuring the passage of time - for example, providing an alarm at regular intervals - timers are used to generate and decode complex pulse trains. A common use is generating a pulse-width modulated signal for motor speed control.

What is a watchdog timer?

Synchronization techniques

Mutex vs Semaphores

Synchronization techniques among threads by IBM.

Object Oriented Programming in C - check this link http://vger.kernel.org/lkml/#s15-3

Toolchains

  • Native: this toolchain runs on the same type of system (sometimes the actual system) as the program it generates.

  • Cross: this toolchain runs on a different type of system than the target, allowing the development to be done on a fast desktop PC and then loaded onto the embedded target for testing. This process is known as cross-compiling.

Cross-Compiling

There are some common build systems, including the following:

  • Pure Makefiles, where the toolchain is usually controlled by the make variable CROSS_COMPILE

  • The GNU build system known as Autotools

  • CMake (https://cmake.org)

Autotools and makefiles are needed to build a basic embedded Linux system. CMake is cross-plaform.

Schematic basics

How to read and understand schematics?

Hardware Debugging tools, Oscilloscope, Multimeter, Logic Analyzer, JTAG

Debugging

Debugging.

Communication Interfaces / Devices

Embedded Peripherals / Interfaces:

  • I2C - synchronous serial interface
  • GPIO
  • Analog - ADC, DAC
  • USB
  • SPI - synchronous serial interface - (complex) LCD, SD flash memory card, (simple) EEPROM)

External Communication Interfaces / Devices:

  • CAN
  • LIN
  • Ethernet
  • Wi-Fi
  • Bluetooth
  • GPS
  • UART

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