Enabling Floating-Point Support in ARM Compiler
To enable floating-point support in ARM Compiler (armcc) for embedded projects, you need to focus on three main areas: compiler options, runtime library selection, and ensuring hardware supports the floating-point operations you intend to use.
Compiler Options
To enable floating-point operations in your code, you often need to configure compiler options. Here are some key options you need to consider:
-mfpu Option: This option specifies the floating-point hardware to be used. For example, if your ARM processor supports the VFPv4-D16 floating-point unit, use:
```markdown
-mfpu=vfpv4-d16
```
-mfloat-abi Option: This option specifies the floating-point ABI (application binary interface) to be used. The two common settings are:
```markdown
-mfloat-abi=soft # Use software floating-point operations
-mfloat-abi=hard # Use hardware floating-point operations
```
Choose hard if your hardware supports it for better performance.
Selecting the Appropriate Floating-Point Libraries
In most cases, you need to link against appropriate libraries that match your floating-point ABI settings. ARM Compiler provides runtime support libraries that are optimized for hard and soft floating-point operations. Ensure your linker configuration reflects these.
Linker Flags: In your project settings, link against the correct libraries. For hard-float ABI, it generally involves specifying libraries like:
```markdown
-larm_cortexM_math_hard
```
For soft-float, the compiler uses different libraries, so this is typically automatic when you specify the ABI correctly.
Ensuring Hardware Support
Double-check that the target ARM microcontroller has the required floating-point unit (FPU). Not all ARM cores, especially those in lower-end Cortex-M series, have an FPU. If your chip has an FPU:
Reference the Datasheet/Reference Manual: Ensure you understand the capabilities and initialization requirements of the FPU.
FPU Initialization: Before using floating-point operations, especially in a real-time operating system (RTOS) environment, initialize the FPU if needed by setting the correct system control block (SCB) register settings as per your microcontroller's specifications.
Example code for initializing FPU on a Cortex-M4 based device:
#include "stm32f4xx.h" // Example for STM32F4
void FPU_Init(void) {
SCB->CPACR |= ((3UL << 10*2) | // Set CP10 Full Access (FPU)
(3UL << 11*2)); // Set CP11 Full Access (FPU)
__DSB(); // Data Synchronization Barrier
__ISB(); // Instruction Synchronization Barrier
}
Testing and Optimization
Once you have configured your toolchain and project settings:
- Validation: Write tests to validate floating-point operations in your application.
- Performance Optimization: Use profiling to ensure your application achieves expected performance. Verify both software and hardware paths are used as intended.
- Debugging: Utilize debugging tools to trace floating-point operations step by step. ARM provides trace and debugging tools that can be integrated into some IDEs.
By carefully setting up compiler options, linking the correct libraries, and ensuring proper hardware configuration and initialization, you'll enable efficient use of floating-point operations in your ARM embedded projects. Be sure to refer to ARM's official documentation for additional details specific to your version of the toolchain.
