Embedded C

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  • Why use C?
    • ‘C’ is a ‘mid-level’, with ‘high-level’ features (such as support for functions and modules) and ‘low-level’ features (such as good access to hardware via pointers)
    • It is efficient
    • Good, well-proven compilers are available for every embedded processor
  • What is Embedded 'C'?
    • Embedded C is an extension of the C language to support Embedded processors
    • The aim is to provide portability and access to common performance-increasing features of processors
    • The Embedded C specification for fixed-point, named address spaces, and named registers gives the programmer direct access to features in the target processor, thereby significantly improving the performance of applications
  • Regular/college-level 'C' programming is different from Embedded System Programming because:
    • An Embedded Micro has limited memory (ROM / RAM)
    • Memory Area is assigned a set of fixed locations for different purposes. ANSI C has no proper support for accessing such locations.
    • Execution Speed is very important for real-time applications created using these Micros. The Micros normally have 8 bit / 16-bit support and no floating-point execution unit is present, hence programming options are limited. Only advanced microcontrollers (PowerPC) provide support for floating-point arithmetic.
    • “Interrupt” service coding is not fully supported in standard C
    • Some micros do not provide stack support

  • A typical embedded system consists of the following major blocks
    • Start-up code
    • Boot Software
    • Application code – The actual software
    • Initialization 
    • Micro peripherals
    • Application
    • RTOS/Scheduler
    • Product Application
    • Interrupts

  • This is the start-up file for the NEC V850SJ2 using internal memory only. This program is using the ca850 assembly language. This start-up file will perform the following actions:
    • Setup default memory setup
    • Ensure all interrupt levels have been service
    • Initialize system Clock Module registers
    • Load base pointer registers tp, gp, sp, and ep
    • Load Mask Register
    • Clear RAM
    • call C Program main function

  • Why start-up code should decide whether to jump to boot software or application software?
    • Start-up checks the application software by calculating the application checksum
    • If the application is corrupted (checksum failure), the control stays in the boot
    • If the application is not corrupted, the control jumps to application

  • Why should the control stay in the boot, if the application checksum fails?
    • If the application code is corrupted, the embedded system can hang. None of the functionality will work.
    • Most of the embedded systems will have an option to re-program the application software.

  • Primary Boot loader
    • This is the most important part of the boot software
    • The communication stack specific routines are loaded at this segment of software

  • Secondary Boot loader
    • The major functionality of this segment is to facilitate reprogramming of the application
    • This part of the boot software has the software segments to erase and flash application
  • What is reprogramming?
    • Reprogramming is a process of re-flashing the application code
    • To achieve reprogramming, the key software blocks required includes:
    • Serial driver – software to communicate with an external programmer
    • Communication Manager – Maybe a vehicle bus protocol or software to decode the data
    • Flash driver – software to erase/write data into Flash
    • Boot software can be:
    • Programmed using specific tools (external flash programmer)
    • Reprogrammed using Boot Upgrader

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