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Linker User Guide

Preface Overview of the Linker Linking Models Supported by armlink Image Structure and Generation Linker Optimization Features Getting Image Details Accessing and Managing Symbols with armlink Scatter-loading Features The scatter-loading mechanism Overview of scatter-loading When to use scatter-loading Linker-defined symbols that are not defined when s Specifying stack and heap using the scatter file Scatter-loading command-line options Scatter-loading images with a simple memory map Scatter-loading images with a complex memory map Scatter file with link to bit-band objects Root execution regions Root execution region and the initial entry point Root execution regions and the ABSOLUTE attribute Root execution regions and the FIXED attribute Methods of placing functions and data at specific Placement of code and data with __attribute__((sec Placement of __at sections at a specific address Restrictions on placing __at sections Automatic placement of __at sections Manual placement of __at sections Placement of a key in flash memory with an __at se Mapping a structure over a peripheral register wit Example of how to explicitly place a named section Placement of unassigned sections with the .ANY mod Placement rules when using multiple .ANY selectors Command-line options for controlling the placement Prioritization of .ANY sections Specify the maximum region size permitted for plac Examples of using placement algorithms for .ANY se Example of next_fit algorithm showing behavior of Examples of using sorting algorithms for .ANY sect Behavior when .ANY sections overflow because of li Placement of veneer input sections in a scatter fi Placement of sections with overlays Reserving an empty region Placement of ARM C and C++ library code Specifying ARM standard C and C++ libraries in a s 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 Creation of regions on page boundaries Overalignment of execution regions and input secti Preprocessing of a scatter file Example of using expression evaluation in a scatte Equivalent scatter-loading descriptions for simple Command-line options for creating simple images Type 1 image, one load region and contiguous execu Type 2 image, one load region and non-contiguous e Type 3 image, multiple load regions and non-contig How the linker resolves multiple matches when proc How the linker resolves path names when processing Scatter file to ELF mapping Scatter File Syntax Linker Command-line Options Linker Steering File Command Reference Via File Syntax

Placement of a key in flash memory with an __at section

7.2.10 Placement of a key in flash memory with an __at section

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.

Placement of the flash key variable in C or C++ code

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

Manual placement of flash execution regions

The following example shows a fragment of a scatter file with manual placement of the flash execution region:
ER_FLASH 0x8000 0x2000
{
  *(+RW)
  *(.ARM.__at_0x8000) ; key
}
Use the linker command-line option --no_autoat to enable manual placement.

Automatic placement of flash execution regions

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.
LR1 0x0
{
  ER_FLASH 0x8000 0x2000
  {
    *(+RO)                   ; other code and read-only data, the
                             ; __at section is automatically selected
  }
  ER2 0x4000
  {
    *(+RW +ZI)               ; .ARM.__at_0x4000 is selected by +RW
  }
}
Related reference
Non-ConfidentialPDF file icon PDF versionARM DUI0377H
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