Understand the Linker Script
The foundation of optimizing linker settings starts with understanding and potentially customizing the linker script. The linker script defines how sections are allocated in memory and can provide opportunities for optimization.
Examine the default linker script used by ARM Linker. Navigate to the script and look for ways to adjust memory allocation.
Customize memory regions to ensure critical sections are placed in faster memory or aligned optimally. Example:
```ld
MEMORY
{
FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 256K
RAM (rwx) : ORIGIN = 0x20000000, LENGTH = 64K
}
SECTIONS
{
.text : {
*(.text)
_(.text._)
} > FLASH
.bss : {
*(.bss)
_(.bss._)
} > RAM
}
```
Eliminate Redundant Code and Data
Minimize unnecessary code and data to reduce the firmware size, leading to faster loading times.
Utilize ARM Compiler's optimization flags to eliminate unused code:
```shell
armcc --optimize --remove_unused_sections
```
Use linker flags to remove unused sections from the final binary:
```shell
--gc-sections
```
Consider refactoring your code to avoid global data and reduce reliance on static variables, especially large ones.
Enable Compression
Applying compression can significantly reduce firmware size, which will reduce load times.
Use ARM Linker to apply basic compression techniques. For example, apply --compress option combined with proper decompression logic in your firmware.
```shell
armlink --compress myFirmware.o -o myFirmware.axf
```
Be mindful of the trade-off between decompression time and load time. Test different algorithms for the best performance in your context.
Optimize Peripheral Initialization
Fine-tuning the order and method of peripheral initialization can also help in reducing load times.
Start critical system peripherals first and delay the initialization of non-essential peripherals. Use lazy initialization where possible. For example:
```c
void initCriticalPeripherals() {
// Initialize peripherals needed at startup
}
void startNonCriticalPeripherals() {
// Initialize peripherals only when needed
}
```
Look into simplifying peripheral clocks and further tuning PLL settings, if applicable, to reduce start-up delay.
Data Alignment and Cache Utilization
Choose the right alignment for data and leverage cache where possible.
Align data to exploit cache line filling and instruction prefetching, if applicable. Example of aligning a buffer:
```c
**attribute**((aligned(8))) uint8_t buffer[256];
```
Investigate and enable prefetch buffers and instruction cache within the ARM architecture to speed up access times dramatically.
Profile and Analyze
Profiler tools can give insights into bottlenecks and areas of improvement.
- Use ARM’s profiling tools to analyze which part of your code and memory is contributing to load times.
- Identify function hot spots and optimize or refactor them. ARM provides tools like the gprof profiler to visualize these metrics.
By implementing these strategies, firmware developers can achieve optimal linker settings using ARM Linker to alleviate load times, contributing to efficient and fast firmware execution on ARM architecture.
