Understanding Linker Script Role
A linker script in MPLAB X is a script that controls the memory layout of the application, specifying where the different sections of code and data are placed in physical memory. When dealing with custom peripherals, it's essential to understand how to adjust or create a linker script that meets the requirements of your custom hardware design.
Identify the Error Messages
Linker script errors often manifest in error messages during the build process. These messages might include information about undefined symbols, section placement errors, or memory overflows. Carefully examine these messages to understand what aspect of the linker script requires attention.
Evaluate the Default Linker Script
Before making changes, understand the default linker script provided by MPLAB X for your specific microcontroller. These scripts are typically found in the compiler's lkr
folder. Familiarize yourself with the syntax and sections such as .text
, .data
, and .bss
.
Create or Modify a Linker Script for Custom Peripherals
Sometimes, the default linker script might not accommodate your custom peripheral's requirements, and modifications are necessary:
Copy the default linker script into your project directory to make customized changes, which prevents altering global settings.
Adjust memory regions to incorporate your peripheral's address range. Use the MEMORY
directive to define these ranges. For example:
```plaintext
MEMORY
{
ROM (rx) : ORIGIN = 0x000000, LENGTH = 0x10000
RAM (rw) : ORIGIN = 0x800000, LENGTH = 0x2000
CUSTOM_IO (rw) : ORIGIN = 0x900000, LENGTH = 0x1000
}
```
Map Custom Peripheral Data Sections
Identify where your custom peripheral needs to reside in memory and map its data sections to these addresses. Use the SECTIONS
command to specify section placement. For example, if your custom I/O device uses special data regions:
```plaintext
SECTIONS
{
.custom_data :
{
KEEP(*(.custom_data))
} > CUSTOM_IO
}
<b>Resolve Undefined Symbols or References</b>
If encountering undefined symbols, ensure that all necessary objects and libraries are included in the project:
- Confirm that the `.c` or assembly files related to custom peripherals are added to the project.
- If external libraries are essential, include them by right-clicking `Libraries` in MPLAB X and adding the appropriate `.a` or `.lib` files.
- Use conditional compilation directives in code to check the availability of certain features or dependencies specific to your hardware.
<b>Optimize and Test Memory Utilization</b>
After making changes, evaluate memory usage:
- Use the map file generated by MPLAB X after the build process to identify memory utilization and ensure sections are fitting within the designated memory regions.
- If memory conflicts arise, re-evaluate allocations in your linker script and restructure sections.
<b>Debugging and Validation</b>
Once changes to the linker script are completed, thoroughly test your application:
- Utilize breakpoints and watch windows in MPLAB X to validate if the data is correctly read from and written to the custom peripheral's memory regions.
- Implement unit tests for peripheral communications, ensuring all pathways function under edge cases.
<b>Document and Version Control Changes</b>
As you modify linker scripts, keep a detailed log of changes, and consider using version control systems like Git to track changes. This practice can facilitate collaborative firmware development and assistance for future reference.
By carefully analyzing error messages, understanding memory layouts, and methodically applying changes, you can effectively tackle linker script errors in MPLAB X for custom peripherals.