ARM Cortex-M33 FPU Configuration Errors and CMSIS DSP Library Function Redefinition
When working with ARM Cortex-M33 microcontrollers, such as the Silicon Labs EFR32MG21, developers often leverage the CMSIS DSP library to implement digital signal processing (DSP) functionalities. However, integrating the CMSIS DSP library with the ARM Cortex-M33 core can lead to two common issues: function redefinition errors in the arm_math.h header file and FPU configuration errors during compilation. These issues arise due to incorrect or incomplete macro definitions, mismatched compiler settings, and improper handling of the ARM Cortex-M33’s Floating Point Unit (FPU). This guide provides a detailed analysis of these issues, their root causes, and step-by-step solutions to resolve them.
FPU Configuration Errors and CMSIS DSP Library Function Redefinition
FPU Configuration Errors
The ARM Cortex-M33 core supports an optional Floating Point Unit (FPU), which accelerates floating-point operations. The CMSIS DSP library relies on the FPU for efficient execution of DSP algorithms. However, if the FPU is not properly configured or if the compiler generates FPU instructions for a device without an FPU, the following error occurs:
#error "Compiler generates FPU instructions for a device without an FPU (check __FPU_PRESENT)"
This error indicates a mismatch between the compiler’s FPU settings and the target microcontroller’s hardware capabilities.
CMSIS DSP Library Function Redefinition
The CMSIS DSP library uses conditional compilation to include or exclude specific functions based on the target ARM core and its features. If the required macros are not defined or are incorrectly defined, the compiler may encounter redefinition errors for functions in the arm_math.h header file. For example:
error: redefinition of 'arm_fir_init_f32'
This issue typically arises when multiple instances of the same function are included due to conflicting macro definitions or improper inclusion of the arm_math.h header file.
Root Causes: Incorrect Macro Definitions and Compiler Settings
Missing or Incorrect Macro Definitions
The CMSIS DSP library relies on several macros to determine the target ARM core, FPU presence, and DSP capabilities. These macros include:
ARM_MATH_CM33: Indicates the use of an ARM Cortex-M33 core.__FPU_PRESENT: Indicates the presence of an FPU.ARM_MATH_DSP: Enables DSP-specific optimizations.ARM_MATH_ARMV8MML: Specifies the ARMv8-M Mainline architecture with DSP extensions.
If these macros are not defined or are incorrectly defined, the CMSIS DSP library may fail to compile or generate redefinition errors.
Mismatched Compiler FPU Settings
The compiler must be configured to generate FPU instructions if the target microcontroller includes an FPU. This configuration is typically controlled by compiler flags such as -mfpu=fpv5-sp-d16 for single-precision FPUs or -mfloat-abi=hard for hardware floating-point support. If these flags are not set or are set incorrectly, the compiler may generate FPU instructions for a device without an FPU, leading to the aforementioned error.
Improper Inclusion of arm_math.h
The arm_math.h header file includes conditional compilation directives to include or exclude specific functions based on the target ARM core and its features. If this header file is included multiple times or if the required macros are not defined before its inclusion, the compiler may encounter redefinition errors.
Resolving FPU Configuration Errors and CMSIS DSP Library Redefinition Issues
Step 1: Verify and Define Required Macros
Ensure that the following macros are defined in your project:
#define ARM_MATH_CM33 // Indicates the use of an ARM Cortex-M33 core
#define __FPU_PRESENT 1 // Indicates the presence of an FPU
#define ARM_MATH_DSP // Enables DSP-specific optimizations
#define ARM_MATH_ARMV8MML // Specifies the ARMv8-M Mainline architecture with DSP extensions
These macros should be defined before including the arm_math.h header file. For example:
#define ARM_MATH_CM33
#define __FPU_PRESENT 1
#define ARM_MATH_DSP
#define ARM_MATH_ARMV8MML
#include "arm_math.h"
Step 2: Configure Compiler FPU Settings
Ensure that the compiler is configured to generate FPU instructions if the target microcontroller includes an FPU. For example, in GCC or Clang, add the following flags to your compiler settings:
-mfpu=fpv5-sp-d16 -mfloat-abi=hard
These flags enable single-precision FPU instructions and hardware floating-point support, respectively. Verify that these settings match the capabilities of your target microcontroller.
Step 3: Check for Multiple Inclusions of arm_math.h
Ensure that the arm_math.h header file is included only once in your project. Use include guards or the #pragma once directive to prevent multiple inclusions. For example:
#ifndef ARM_MATH_H
#define ARM_MATH_H
#include "arm_math.h"
#endif
Step 4: Validate FPU Presence and Configuration
Verify that the target microcontroller includes an FPU by checking its datasheet or reference manual. For example, the Silicon Labs EFR32MG21 microcontroller includes a single-precision FPU. Ensure that the __FPU_PRESENT macro is defined correctly based on the target hardware.
Step 5: Debugging and Testing
After applying the above steps, rebuild your project and test the CMSIS DSP library functionalities. If the issues persist, enable verbose compiler output to identify any remaining configuration errors or mismatched settings.
Summary of Key Points
| Issue | Root Cause | Solution |
|---|---|---|
| FPU configuration error | Mismatched compiler FPU settings | Define __FPU_PRESENT and set compiler flags |
| Function redefinition errors | Missing or incorrect macro definitions | Define ARM_MATH_CM33, ARM_MATH_DSP, etc. |
Multiple inclusions of arm_math.h |
Improper header file inclusion | Use include guards or #pragma once |
By following these steps, you can resolve FPU configuration errors and CMSIS DSP library function redefinition issues when working with ARM Cortex-M33 microcontrollers. Proper macro definitions, compiler settings, and header file management are critical to ensuring a successful integration of the CMSIS DSP library.
