Pi Zi Heng Embedded: ARM Cortex-M Files (2) - Link File (.icf)

　　At this point, a basic linker file is done. Isn’t it so easy?

Extra 1: Custom section

　　For those who have read this far with patience, Pi Ziheng must give a big reward. The previous part is about how to deal with the system default segment, so is it possible to customize the segment in the code? Imagine that you have such a requirement, you need to open a 1KB updateable data area in your application, you want to specify this data area to the address range of 0x18000 - 0x183ff, you need to define a 4-byte read-only config block constant in the application to point to the first address of this updateable data area (this config block will only be updated by an external debugger or bootloader), how to do it?

// In the C file

/////////////////////////////////////////////////////

// Use the @ operator to specify the variable myConfigBlock[4] to be placed in the custom .myBuffer section

const uint8_t myConfigBlock[4] @ ".myBuffer" = {0x00, 0x01, 0x02, 0x03};

// Linker file

/////////////////////////////////////////////////////

// Customize the specified mySection_region and put .myBuffer into this region

define region mySection_region = mem:[from 0x0x18000 to 0x183ff];

place at start of mySection_region { readonly section .myBuffer };

　　The above has achieved the goal of putting constants in the code into a custom segment? So how do you put functions in the code into a custom segment? Read on

// In the C file

/////////////////////////////////////////////////////

// Use #pragma location to specify the function myFunction() to be placed in the custom .myTask section

#pragma location = ".myTask"

void myFunction(void)

{

    __NOP();

}

// Linker file

/////////////////////////////////////////////////////

// Put .myTask into mySection_region

place in mySection_region { readonly section .myTask };

　　It seems that the work is done. There is one last thing to note. If myConfigBlock is not referenced in the code, the IDE may ignore this variable when linking (IDE thinks it is useless, so it optimizes it). So how can I force the IDE to link myConfigBlock? IAR has left a backdoor. In the Keep symbols input box in options->Linker->Input tab, fill in the object name you want to force link (note that it is the object name in the code, not the custom segment name in the linker file).

Note: For more details about the extra content, please refer to the Pragma directives section in the IAR SystemsEmbedded Workbench xxxarmdocEWARM_DevelopmentGuide.ENU.pdf document in the IAR software installation directory.