Understanding Section Placement Issues
In ARM Linker, section placement issues often arise when the memory map specified doesn't align with the actual needs of your firmware binary or when the allocations specified in the scatter file conflict with each other. Misplaced sections can lead to inefficient use of memory or runtime errors, making it imperative to resolve these issues effectively.
Identifying the Problematic Sections
Check for Warnings and Errors: The ARM Linker will often provide warnings or errors related to section placement that can give clues about what's wrong. Reviewing these messages can help you pinpoint the root cause.
Utilize Map Files: Generate a map file using ARM Linker to get a comprehensive view of how sections are placed. This file can show where each section resides in memory, aiding in identifying any overlaps or misalignments.
Analyzing Scatter Files
Review the Scatter File: The scatter file acts as a blueprint for placing code and data into different memory sections. Ensure that this file accurately reflects the architecture's address space and the memory layout you are targeting.
Example Scatter File: Here's a basic outline of how a scatter file might look:
LR_IROM1 0x08000000 0x00080000 { ; load region size_region
ER_IROM1 0x08000000 0x00080000 { ; load address = execution address
*.o (RESET, +First) ; Initial entry point
*(InRoot$$Sections) ; All unassigned sections
}
ER_IRAM1 0x20000000 0x00020000 {
*.o (+RO)
*(+RW +ZI)
}
}
- Ensure Memory Regions are Correct: Double-check the definitions of memory regions like ROM and RAM in your scatter file. Misdefining these can lead to incorrect placements.
Adjusting Section Attributes
- Customize Attributes: Modify the section attributes in the source code or header files using
#pragma directives or section attributes to ensure they align with your scatter file allocations.
int var1 __attribute__((section("my_section"))) = 0;
- Use
#pragma to Control Placement: In some cases, using #pragma directly in the code can be useful:
#pragma arm section code="my_code_section", rodata="my_rodata_section"
Resolving Overlaps and Conflicts
Adjust Base Addresses and Sizes: In cases of overlap, consider adjusting the base addresses or sizes of sections to resolve conflicts. Base addresses should align with the memory boundaries and should be appropriately non-overlapping.
Reallocate or Resize Sections: If certain sections are too large to fit in their designated space, consider either reallocating them to another memory section or reducing their size (if feasible).
Optimizing the Memory Configuration
Optimize for Usage: Ensure that the most frequently accessed sections, such as interrupt vectors, are placed in fast access memory areas, like SRAM, for optimized performance. This might involve adjusting your scatter file to prioritize these sections.
Memory Protection Units (MPUs): If your microcontroller supports it, use MPUs to protect certain regions of memory, ensuring that your sections are correctly placed within protected or non-protected areas, as required.
Testing and Verification
Rebuild and Test: After making adjustments, rebuild the project and thoroughly test the firmware to ensure that the changes resolved the placement issues without introducing new ones.
Use Debugger: Employ a debugger to step through code execution in memory, confirming whether sections reside in the expected locations.
By carefully tailoring your scatter file, adjusting section attributes, and verifying with map files, you can effectively resolve section placement issues in ARM Linker for firmware binaries. Such meticulous strategies ensure efficient memory usage and robust firmware operation.
