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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

When to use scatter-loading

7.1.2 When to use scatter-loading

Scatter-loading is usually required for implementing embedded systems because these use ROM, RAM, and memory-mapped peripherals.

Situations where scatter-loading is either required or very useful:
Complex memory maps
Code and data that must be placed into many distinct areas of memory require detailed instructions on where to place the sections in the memory space.
Different types of memory
Many systems contain a variety of physical memory devices such as flash, ROM, SDRAM, and fast SRAM. A scatter-loading description can match the code and data with the most appropriate type of memory. For example, interrupt code might be placed into fast SRAM to improve interrupt response time but infrequently-used configuration information might be placed into slower flash memory.
Memory-mapped peripherals
The scatter-loading description can place a data section at a precise address in the memory map so that memory mapped peripherals can be accessed.
Functions at a constant location
A function can be placed at the same location in memory even though the surrounding application has been modified and recompiled. This is useful for jump table implementation.
Using symbols to identify the heap and stack
Symbols can be defined for the heap and stack location when the application is linked.
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