tick_conversion.h
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/*
* Copyright (C) 2016 Eistec AB
*
* 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.
*/
/**
* @ingroup sys_xtimer
*
* @{
* @file
* @brief xtimer tick <-> seconds conversions for different values of XTIMER_HZ
* @author Joakim Nohlgård <joakim.nohlgard@eistec.se>
*/
#ifndef XTIMER_TICK_CONVERSION_H
#define XTIMER_TICK_CONVERSION_H
#ifndef XTIMER_H
#error "Do not include this file directly! Use xtimer.h instead"
#endif
#include "div.h"
#ifdef __cplusplus
extern "C" {
#endif
/* Some optimizations for common timer frequencies */
#if (XTIMER_SHIFT != 0)
#if (XTIMER_HZ % 15625 != 0)
#error XTIMER_HZ must be a multiple of 15625 (5^6) when using XTIMER_SHIFT
#endif
#if (XTIMER_HZ > 1000000ul)
#if (XTIMER_HZ != (1000000ul << XTIMER_SHIFT))
#error XTIMER_HZ != (1000000ul << XTIMER_SHIFT)
#endif
/* XTIMER_HZ is a power-of-two multiple of 1 MHz */
/* e.g. cc2538 uses a 16 MHz timer */
inline static uint32_t _xtimer_ticks_from_usec(uint32_t usec) {
return (usec << XTIMER_SHIFT); /* multiply by power of two */
}
inline static uint64_t _xtimer_ticks_from_usec64(uint64_t usec) {
return (usec << XTIMER_SHIFT); /* multiply by power of two */
}
inline static uint32_t _xtimer_usec_from_ticks(uint32_t ticks) {
return (ticks >> XTIMER_SHIFT); /* divide by power of two */
}
inline static uint64_t _xtimer_usec_from_ticks64(uint64_t ticks) {
return (ticks >> XTIMER_SHIFT); /* divide by power of two */
}
#else /* !(XTIMER_HZ > 1000000ul) */
#if ((XTIMER_HZ << XTIMER_SHIFT) != 1000000ul)
#error (XTIMER_HZ << XTIMER_SHIFT) != 1000000ul
#endif
/* 1 MHz is a power-of-two multiple of XTIMER_HZ */
/* e.g. ATmega2560 uses a 250 kHz timer */
inline static uint32_t _xtimer_ticks_from_usec(uint32_t usec) {
return (usec >> XTIMER_SHIFT); /* divide by power of two */
}
inline static uint64_t _xtimer_ticks_from_usec64(uint64_t usec) {
return (usec >> XTIMER_SHIFT); /* divide by power of two */
}
inline static uint32_t _xtimer_usec_from_ticks(uint32_t ticks) {
return (ticks << XTIMER_SHIFT); /* multiply by power of two */
}
inline static uint64_t _xtimer_usec_from_ticks64(uint64_t ticks) {
return (ticks << XTIMER_SHIFT); /* multiply by power of two */
}
#endif /* defined(XTIMER_SHIFT) && (XTIMER_SHIFT != 0) */
#elif XTIMER_HZ == (1000000ul)
/* This is the most straightforward as the xtimer API is based around
* microseconds for representing time values. */
inline static uint32_t _xtimer_usec_from_ticks(uint32_t ticks) {
return ticks; /* no-op */
}
inline static uint64_t _xtimer_usec_from_ticks64(uint64_t ticks) {
return ticks; /* no-op */
}
inline static uint32_t _xtimer_ticks_from_usec(uint32_t usec) {
return usec; /* no-op */
}
inline static uint64_t _xtimer_ticks_from_usec64(uint64_t usec) {
return usec; /* no-op */
}
#elif XTIMER_HZ == (32768ul)
/* This is a common frequency for RTC crystals. We use the fact that the
* greatest common divisor between 32768 and 1000000 is 64, so instead of
* multiplying by the fraction (32768 / 1000000), we will instead use
* (512 / 15625), which reduces the truncation caused by the integer widths */
inline static uint32_t _xtimer_ticks_from_usec(uint32_t usec) {
return div_u32_by_15625div512(usec);
}
inline static uint64_t _xtimer_ticks_from_usec64(uint64_t usec) {
return div_u64_by_15625div512(usec);
}
inline static uint32_t _xtimer_usec_from_ticks(uint32_t ticks) {
/* return (usec * 15625) / 512; */
/* Using 64 bit multiplication to avoid truncating the top 9 bits */
uint64_t usec = (uint64_t)ticks * 15625ul;
return (usec >> 9); /* equivalent to (usec / 512) */
}
inline static uint64_t _xtimer_usec_from_ticks64(uint64_t ticks) {
/* return (usec * 15625) / 512; */
uint64_t usec = (uint64_t)ticks * 15625ul;
return (usec >> 9); /* equivalent to (usec / 512) */
}
#else
/* No matching implementation found, try to give meaningful error messages */
#if ((XTIMER_HZ % 15625) == 0)
#error Unsupported hardware timer frequency (XTIMER_HZ), missing XTIMER_SHIFT in board.h? See xtimer.h documentation for more info
#else
#error Unknown hardware timer frequency (XTIMER_HZ), check board.h and/or add an implementation in sys/include/xtimer/tick_conversion.h
#endif
#endif
#ifdef __cplusplus
}
#endif
#endif /* XTIMER_TICK_CONVERSION_H */