busy_wait.h

/*
 * Copyright (C) 2024 ML!PA Consulting GmbH
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */
 
#pragma once
 
#include <stdint.h>
#include "periph_conf.h"
#include "time_units.h"
 
#ifdef __cplusplus
extern "C" {
#endif
 
#ifndef CPU_CYCLES_PER_LOOP
#define CPU_CYCLES_PER_LOOP 3
#endif
 
static inline void busy_wait(unsigned loops)
{
    while (loops) {
        /* This empty inline assembly should be enough to convince the
         * compiler that the loop cannot be optimized out. Tested with
         * GCC 12.2 and clang 16.0.0 successfully. */
        __asm__ __volatile__ (
            ""
            : /* no outputs */
            : /* no inputs */
            : /* no clobbers */
        );
        loops--;
    }
}
 
static inline void busy_wait_us(unsigned usec)
{
    unsigned loops = ((uint64_t)usec * CLOCK_CORECLOCK)
                   / (US_PER_SEC * CPU_CYCLES_PER_LOOP);
    busy_wait(loops);
}
 
#ifdef __cplusplus
}
#endif