Understand the Causes of Firmware Size Increase
Understanding why the firmware size increases when using the STM32 HAL is crucial. The HAL (Hardware Abstraction Layer) can substantially increase code size due to its comprehensive, generic code. This is designed to maximize hardware compatibility but can lead to non-optimized sections, unused functions, and extra debugging code. Before addressing the issue, identify which parts of the HAL or project contribute most to the size increase. Utilize compiler flags for listing symbols and sizes, such as -Xlinker --print-map.
Enable Compiler Optimizations
Harnessing compiler optimization flags can help decrease the size of your firmware. For instance, you can use:
-O2
This flag enables various optimizations for speed and size, although the final binary might not be as small as possible. For size-specific optimization, use:
-Os
This flag applies all -O2 optimizations plus those that reduce code size. Always test the build to ensure the device behaves correctly after optimization.
Reduce Unused HAL Modules
The HAL libraries are modular, meaning you don't need to include components that you don't use.
In stm32f4xx_hal_conf.h or equivalent configure file, comment out the unused HAL module macros. For instance, if you don't need ADC functionality, ensure the following macro is commented out:
```c
//#define HAL_ADC_MODULE_ENABLED
```
Similarly, review the CMSIS library and exclude unnecessary functions.
Leverage Link-Time Optimization (LTO)
Link-Time Optimization can substantially reduce the firmware size by removing unused functions and variables spread across different files.
To enable LTO, add the following to your makefile or compilation settings:
```
-flto
```
Be sure to recompile your entire project and check for any unexpected behavior, as LTO can sometimes cause unforeseen issues.
Minimize Use of Dynamic Memory
While STM32 applications typically don't rely heavily on dynamic memory due, you should still strive to minimize its usage in favor of static memory allocation. Static memory allocation not only saves size but also improves predictability and stability.
- Avoid functions like
malloc or free if possible.
- If dynamic allocation is necessary, ensure that you're not over-allocating or failing to free memory efficiently.
Disable Debugging and Assertions
Disabling the debugging infrastructure and runtime assertions in stm32f4xx_hal_conf.h can save space:
Use Custom Handlers and Drivers
If HAL-generated code is still too large after stripping unused parts, consider incorporating custom minimal drivers:
- Create a custom lightweight driver for your frequently used peripherals. Developing this aspect reduces dependency on large HAL libraries.
- Replace the HAL API calls in your application with calls to your custom drivers, ensuring these are tightly tailored to your needs.
Profile and Analyze
Before making changes, make sure to profile your application to better understand where improvements can be made:
- Utilize tools like
nm, size, or more advanced platforms like STM32CubeMonitor to assess the sections that contribute to larger firmware size.
- Consider investing time in analyzing the memory footprint using an RTOS-aware profiler if applicable.
Addressing a firmware size increase requires targeted strategies that balance optimization, functionality, performance, and code maintainability. By selectively applying these techniques, you can effectively manage firmware size while maintaining the integrity of your embedded project.
