Identify the Cause of the Multiple Definition Error
- Multiple definition errors typically occur when the same identifier is defined more than once in your program. This usually happens when multiple translation units or object files each contain a definition of the same function or variable.
- In the context of embedded systems using the SysTick timer, `SysTick_Handler` might be defined in multiple files, or it might be included inappropriately via a header.
Check the Startup Code
- Your startup code or hardware abstraction library might be providing a default definition of `SysTick_Handler`. Ensure you are not unintentionally defining it again in your application code.
- Commonly, the `SysTick_Handler` is part of the interrupt vector table in assembly or in a C/C++ file dedicated to initialization. Locate this file to understand how `SysTick_Handler` is being defined and modify it if necessary.
Utilize Weak Symbols
- If the `SysTick_Handler` is defined as a weak symbol in the startup file, you can create your own definition to override this weak definition. Ensure your function prototype matches exactly with the weakly defined handler.
extern "C" void SysTick_Handler(void) __attribute__((weak));
extern "C" void SysTick_Handler(void) {
// Handle SysTick interrupt
}
Guard Against Multiple Definitions in Code
- Use `#ifndef`, `#define`, and `#endif` preprocessor directives to ensure `SysTick_Handler` is not defined multiple times across your project. This is effective particularly when dealing with header files.
#ifndef SYSTICK_HANDLER_H
#define SYSTICK_HANDLER_H
extern "C" void SysTick_Handler(void);
#endif // SYSTICK_HANDLER_H
Use Namespace to Avoid Collision
- If `SysTick_Handler` is defined across different modules, using C++ namespaces can help prevent naming conflicts. Define your handler within a specific namespace.
namespace MyFirmware {
extern "C" void SysTick_Handler() {
// Custom handler code
}
}
// Usage in code
using namespace MyFirmware;
Linking Options and Debugging
- When linking, use the linker options to inspect where definitions are being pulled from. Tools like `nm` or `objdump` can help analyze object files to see multiple definitions.
- Run these tools from the command line to view symbol tables and find where `SysTick_Handler` is being defined.
nm my_project.elf | grep SysTick_Handler
Consolidate and Refactor
- If your project has grown complex, consolidate your interrupt handlers into a unified file location or module. Keeping all ISR (Interrupt Service Routines) in a single file can greatly reduce the risk of multiple definitions.
