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Linker User Guide

Conventions and feedback Overview of the linker Linking models supported by armlink Image structure and generation Using linker optimizations Getting information about images Accessing and managing symbols with armlink Using scatter files About scatter-loading When to use scatter-loading Scatter-loading command-line option Images with a simple memory map Images with a complex memory map Linker-defined symbols that are not defined when s Specifying stack and heap using the scatter file What is a root region? Creating root execution regions Using the FIXED attribute to create root regions Placing functions and data at specific addresses Placing a named section explicitly using scatter-l Placing unassigned sections with the .ANY module s Examples of using placement algorithms for .ANY se Example of next_fit algorithm showing behavior of Examples of using sorting algorithms for .ANY sect Selecting veneer input sections in scatter-loading Using __attribute__((section("name"))) t Using __at sections to place sections at a specifi Restrictions on placing __at sections Automatic placement of __at sections Manual placement of __at sections Placing a key in flash memory using __at Placing a structure over a peripheral register usi Placement of sections with overlays About placing ARM C and C++ library code Example of placing code in a root region Example of placing ARM C library code Example of placing ARM C++ library code Example of placing ARM library helper functions Reserving an empty region About creating regions on page boundaries Overalignment of execution regions and input secti Using preprocessing commands in a scatter file Expression evaluation in scatter files Using expression evaluation in a scatter file to a Equivalent scatter-loading descriptions for simple Type 1 image, one load region and contiguous execu Type 2 image, one load region and non-contiguous e Type 3 image, two load regions and non-contiguous Scatter file to ELF mapping

Placing a key in flash memory using __at

Placing a key in flash memory using __at

Some flash devices require a key to be written to an address to activate certain features. An __at section provides a simple method of writing a value to a specific address.

Assuming a device has flash memory from 0x8000 to 0x10000 and a key is required in address 0x8000. To do this with an __at section, you must declare a variable so that the compiler can generate a section called .ARM.__at_0x8000.

Example 24. Placement of the flash key variable in C or C++ code

// place flash_key in a section called .ARM.__at_0x8000
long flash_key __attribute__((section(".ARM.__at_0x8000")));

The following example shows a scatter file with manual placement of the flash execution region:

Example 25. Manual placement of flash execution regions

ER_FLASH 0x8000 0x2000
{
    *(+RO)
    *(.ARM.__at_0x8000) ; key
}

Use the linker command-line option --no_autoat to enable manual placement.

The following example shows a scatter file with automatic placement of the flash execution region. Use the linker command-line option --autoat to enable automatic placement.

Example 26. Automatic placement of flash execution regions

ER_FLASH 0x8000 0x2000
{
    *(+RO)               ; other code and read-only data, the
                         ; __at section is automatically selected
}

Copyright © 2007-2008, 2011-2012 ARM. All rights reserved.ARM DUI 0377D
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