Embedded System Architecture

Embedded System:-

     Embedded System is the combination of Hardware and Software. Embedded System consists of hardware components like,

     ·  Processor

     ·  Peripherals

     ·  Controllers

     ·  Buses

Processor:-

     ·  Processor is the heart of the Embedded Systems

     ·  Processor controls the Embedded Device

     ·  Ex:- 8085, 8086

Peripherals:-

     ·   Any Embedded System that interact with the outside world need some form of peripheral devices.

     ·   A peripheral device performs input and output functions for the chip.

     ·   Ex:- Timer, ADC, UART, SPI, I2C, CAN and WDT

Controllers:-

There are 2 types of controllers

    1. Memory Controllers

    2. Interrupt Controllers

Memory Controllers:-

    ·  Memory Controllers connect different types of memory to the bus.

    ·  On Reset, Memory controllers are initialized.

    ·  Ex:-  In ARM Platform, the different types of memory like Flash, RAM, EEPROM, DRAM are connected to memory controllers.

Memory:-

     An Embedded System consists some form of memory to store and execute programs.

Cache:-

     It is the memory device, which places in between CPU Core and Main Memory.

Interrupt Controllers:-

     An Interrupt Controller provides programmable software to determine which peripheral or device can interrupt the processor.

Buses:-

     Buses are used to communicate between the different parts of the device.

     In ARM Processor, AMBA is on-chip internal bus is used to connect the processor and peripherals together.

There are 2 types of Buses,

1.  AHB Bus

2.  VPB Bus

      ·  A Bus has two architecture levels. The First is a physical level that covers the electrical characteristics and the bus width (16, 32 and 64 bits).

      ·  The Second level deals with the Protocol.

Embedded System Software Components:-

Initialization Code:-

    ·  Initialization Code is the first code executed on the board.

    ·  It sets up the minimal parts of the board and give the control to an operating system.

    ·  There are different tasks are done in 3 Phases :

1.  Initial Hardware Design

2.  Diagnostics

3.  Booting

Initial Hardware Design:-

    ·  It initializes the CPU Clock

    ·  It initializes the Memory

    ·  It initializes the stack pointers for all the modes

    ·  It gives the basic branch instructions for all the interrupts and exceptions

   ·   It remaps the memory

Diagnostics:-

     The primary purpose of Diagnostic code is fault identification and isolation.

Booting:-

     Booting involves loading an operating system and give the control to an Operating System.

Firmware:-

     A System may require firmware support to boot an operating system.

     Firmware is an important part of an embedded system in which the first code is ported and executed on a new platform.

     There are 2 popular industry standard firmware packages for ARM based systems.

        1.  ARM Firmware Suit

        2.  Red Hat’s Red Boot

     The firmware is deeply embedded low level software that provides an interface between the hardware and the operating system.

     It resides in the ROM and executes when power is applied to the embedded hardware system.

Device Drivers:-

    The Device Drivers provide a consistent software interface to the peripherals on the hardware device.

    The HAL (Hardware Abstraction Layer) software communicates with the specific hardware peripherals called a Device Driver.

    A Device Driver provides a standard application programming interface (API) to read and write to a specific peripherals like USB, UART, CAN, SPI etc.

    We can send the commands through a Command Line Interpreter (CLI) to target platform.

    For Embedded Systems, the CLI is commonly controlled through a Host terminal application.

Operating System:-

    The Operating System provides an Infrastructure to control applications and manage hardware resources.

Operating System organizes the System Resources :

    ·  Peripherals

    ·  Memory

Operating System classified into two types :

     1.  RTOS (Real Time Operating System)

     2.  GPOS (General Purpose Operating System)

RTOS:-

     ·   RTOS provides guaranteed response times to an events.    

     ·   Systems running on RTOS generally don’t have Secondary Storage.

GPOS:-

     ·  It requires memory management unit and it has secondary storage

     ·  Ex:- Linux, Windows

Embedded Operating System:-

     ·  The initialization sets up the variables, data structures and hardware devices by the operating system.

     ·  All interrupts and exceptions require a handler. For unused interrupts and exceptions a dummy handler must be installed.

     ·  A periodic timer is required for pre-emptive operating system.

     ·  A scheduler is an algorithm that schedules the tasks to execute.

    ·   A context switch saves the state of the current task and loads the state of the next task.




  Article by:-

   Venkatesh Enjam
   Project Engineer - 1
   CDAC R & D
   Bangalore 

      

posted data:- 05/02/2014