STM32 function profiling using the cycle counter

STM32 clock counter profiling.h

// Quick and dirty profiler for STM32 devices with the DWT cycle counter
// Computes the percentage of processor time spent in a function.  Best suited for functions that are called routinely.
// Can be used in mixed C/C++ code. 

// profile.h
#pragma once

inline uint32_t perfCounter() {
    return DWT->CYCCNT;
}


#define PROFILE_VALUE(name) name##_percent

#ifdef __cplusplus

#define PROFILE_DECLARE(name) \
    extern "C" { \
        float name##_percent; \
    }

#define PROFILE_USE(name) \
    extern "C" float name##_percent;

#else

#define PROFILE_DECLARE(name) \
    float name##_percent; \
    

#define PROFILE_USE(name) \
    float name##_percent;

#endif


#define PROFILE_PERCENT(name, x) {\
    static uint32_t name##_prev = 0; \
    uint32_t before = perfCounter(); \
    (x); \
    uint32_t after = perfCounter(); \
    uint32_t duration = (after-before); \
    name##_percent = (duration*100)/(after - name##_prev); \
    name##_prev = after; \
}


/*
 * How to use
 *
 * In the code to be profiled, declare the profiling tag in global scope:
 *
 * PROFILE_DECLARE(my_function)
 * 
 * The name you choose is up to you, but easiest if it is named after the function you are profiling. 
 * 
 * Wrap the call to `my_function` in PROFILE_PERCENT
 *
 * Before:
 *   ...
 *   my_function(1,2,3);
 *   ...
 *
 * After:
 *
 * PROFILE_PERCENT(my_function(1,2,3));
 *
 * To retrieve the profile percentage value, add code to your main app, e.g. an Arduino sketch.
 *
 * #include <profile.h>
 * PROFILE_USE(my_function);
 *
 * Then use `PROFILE_VALUE(my_function)` to retrieve the current profiled percentage, as a float. E.g. 
 *
 * Serial.print("my_function takes ");
 * Serial.print(PROFILE_VALUE(my_function));
 * Serial.print(" percent");
 *
 * The profiler is best suited to functions that run regularly. The profiler determines the percentage of MCU time 
 * spent inside the function compared to the time spent outside the function.
 */