[hemmerling] AVR Microcontrollers Expertness 3/4 - Software Design for the Atmel Platform

Related pages:

• The Atmel AVR Family ( by Microchip Technology Inc. ) with Focus on ATxmega, ATmega, ATtiny and the Arduino / Freeduino Platform.
• The Arduino / Freeduino Platform with Atmel ATmega, Microchip PIC, ARM, Freescale Coldfire.
• Atmel ATmega, ATtiny, AT90 & ATmega ( by Microchip Technology Inc. ) on the Arduino / Freeduino Platform.
• Atmel ATxmega "XMEGA" ( by Microchip Technology Inc. ) - This page deals with software tools which are suitable both for ATxmega and for ATmega, ATtiny.

• Question: How to include “C” headers in a “C++” project ?
• Issue: Many C++ books don´t cover the topic .
• Solution:

  extern ( 
  #include "my_c_header.h" 
  )

• Recommended readling:
  • Microoft MSDN Library "Using extern to Specify Linkage".

• How To display a simple 128×32 logo ?
• Solution:
  • On the Windows / Linux host computer, Create a BW image using GIMP. Store it in the “XBM” format.
  • Write a little C program to convert it ( on the host Windows / Linux computer ) to a format native for the display.
• Recommended reading:
  • EN.Wikipedia "X BitMap" ( XBM ).

• Issue: AVR 8-bit CPUs work with 16-bit pointers.
  • In RAM, the 16-bit pointers limit access to 64K bytes.
  • In Flash, the 16-bit pointers limit access to 128K ( 64K words ).
  • However there are pointer extension registers ( RAMPZ ) that easily let you break these barriers.
• WinAVR GNU-C/C++:
  • Make yourself familiar with the -mrelax compiler (linker) option, which is necessary to compile and link projects with > 128 Kbytes Flash.
  • Read-only data arrays stored in Flash memory are limited to < 32 Kbytes size. Explanations:
    1. sizeof(int) = 2.
    2. The requirement that array indices are signed by definition (so expressions like “pointer[-1]” can work).
    3. The restriction that GCC wants to potentially allow byte access to all arrays/pointers.
• CodeVisionAVR:
  • The commercial HP Infotech "CodeVisionAVR Compiler" supports Flash access for memory of 256kb flash and greater, with its Medium and Large memory models.
• Limits:
• Recommended reading:
  • mikrocontroller.net, Thread "RAMPZ und AVR-GCC".
  • AVR Freaks Forum, Thread "How to use morepgmspace.h".
  • AVR Freaks Forum, Thread "128 KBytes Flash limit / barrier of AVR-GCC ?" #.
  • AVR C Runtime Library - Patches: patch #6352, Far pointer library.
  • AVR Libc - Frequently Asked Questions , section "On a device with more than 128 KiB of flash, how to make function pointers work?".

• OpenDirectory "Top: Computers: Hardware: Components: Processors: AVR.