ARM Compiler toolchain Using the Linker - ARM Information Center

8.23 Placing a key in flash memory using __at
8.23.1 See also
Using scatter files
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.
The following example shows a scatter file with manual placement of the flash execution
region:
ER_FLASH 0x8000 0x2000
{
*(+RO)
*(.ARM.__at_0x8000) ; key
}
Example 8-13 Manual placement of flash execution regions
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 8-14 Automatic placement of flash execution regions
ER_FLASH 0x8000 0x2000
{
*(+RO) ; other code and read-only data, the
; __at section is automatically selected
}
Tasks
• Placing sections with FIRST and LAST attributes on page 4-21
• Using __at sections to place sections at a specific address on page 8-37.
Concepts
• Automatic placement of __at sections on page 8-39
• Manual placement of __at sections on page 8-41.
Linker Reference:
• About execution region descriptions on page 4-8.
Reference
Linker Reference:
• --autoat, --no_autoat on page 2-17.
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