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1 1 : /* 2 : * Copyright (c) 2023 Zephyr Project 3 : * 4 : * SPDX-License-Identifier: Apache-2.0 5 : */ 6 : 7 : /** 8 : * @file 9 : * @brief Representation of nanosecond resolution elapsed time and timestamps in 10 : * the network stack. 11 : * 12 : * Inspired by 13 : * https://github.com/torvalds/linux/blob/master/include/linux/ktime.h and 14 : * https://github.com/torvalds/linux/blob/master/[tools/]include/linux/time64.h 15 : * 16 : * @defgroup net_time Network time representation. 17 : * @since 3.5 18 : * @version 0.1.0 19 : * @ingroup networking 20 : * @{ 21 : */ 22 : 23 : #ifndef ZEPHYR_INCLUDE_NET_NET_TIME_H_ 24 : #define ZEPHYR_INCLUDE_NET_NET_TIME_H_ 25 : 26 : /* Include required for NSEC_PER_* constants. */ 27 : #include <zephyr/sys_clock.h> 28 : 29 : #ifdef __cplusplus 30 : extern "C" { 31 : #endif 32 : 33 : /** 34 : * @brief Any occurrence of net_time_t specifies a concept of nanosecond 35 : * resolution scalar time span, future (positive) or past (negative) relative 36 : * time or absolute timestamp referred to some local network uptime reference 37 : * clock that does not wrap during uptime and is - in a certain, well-defined 38 : * sense - common to all local network interfaces, sometimes even to remote 39 : * interfaces on the same network. 40 : * 41 : * This type is EXPERIMENTAL. Usage is currently restricted to representation of 42 : * time within the network subsystem. 43 : * 44 : * @details Timed network protocols (PTP, TDMA, ...) usually require several 45 : * local or remote interfaces to share a common notion of elapsed time within 46 : * well-defined tolerances. Network uptime therefore differs from time 47 : * represented by a single hardware counter peripheral in that it will need to 48 : * be represented in several distinct hardware peripherals with different 49 : * frequencies, accuracy and precision. To co-operate, these hardware counters 50 : * will have to be "syntonized" or "disciplined" (i.e. frequency and phase 51 : * locked) with respect to a common local or remote network reference time 52 : * signal. Be aware that while syntonized clocks share the same frequency and 53 : * phase, they do not usually share the same epoch (zero-point). 54 : * 55 : * This also explains why network time, if represented as a cycle value of some 56 : * specific hardware counter, will never be "precise" but only can be "good 57 : * enough" with respect to the tolerances (resolution, drift, jitter) required 58 : * by a given network protocol. All counter peripherals involved in a timed 59 : * network protocol must comply with these tolerances. 60 : * 61 : * Please use specific cycle/tick counter values rather than net_time_t whenever 62 : * possible especially when referring to the kernel system clock or values of 63 : * any single counter peripheral. 64 : * 65 : * net_time_t cannot represent general clocks referred to an arbitrary epoch as 66 : * it only covers roughly +/- ~290 years. It also cannot be used to represent 67 : * time according to a more complex timescale (e.g. including leap seconds, time 68 : * adjustments, complex calendars or time zones). In these cases you may use 69 : * @ref timespec (C11, POSIX.1-2001), @ref timeval (POSIX.1-2001) or broken down 70 : * time as in @ref tm (C90). The advantage of net_time_t over these structured 71 : * time representations is lower memory footprint, faster and simpler scalar 72 : * arithmetic and easier conversion from/to low-level hardware counter values. 73 : * Also net_time_t can be used in the network stack as well as in applications 74 : * while POSIX concepts cannot. Converting net_time_t from/to structured time 75 : * representations is possible in a limited way but - except for @ref timespec - 76 : * requires concepts that must be implemented by higher-level APIs. Utility 77 : * functions converting from/to @ref timespec will be provided as part of the 78 : * net_time_t API as and when needed. 79 : * 80 : * If you want to represent more coarse grained scalar time in network 81 : * applications, use @ref time_t (C99, POSIX.1-2001) which is specified to 82 : * represent seconds or @ref suseconds_t (POSIX.1-2001) for microsecond 83 : * resolution. Kernel @ref k_ticks_t and cycles (both specific to Zephyr) have 84 : * an unspecified resolution but are useful to represent kernel timer values and 85 : * implement high resolution spinning. 86 : * 87 : * If you need even finer grained time resolution, you may want to look at 88 : * (g)PTP concepts, see @ref net_ptp_extended_time. 89 : * 90 : * The reason why we don't use int64_t directly to represent scalar nanosecond 91 : * resolution times in the network stack is that it has been shown in the past 92 : * that fields using generic type will often not be used correctly (e.g. with 93 : * the wrong resolution or to represent underspecified concepts of time with 94 : * unclear syntonization semantics). 95 : * 96 : * Any API that exposes or consumes net_time_t values SHALL ensure that it 97 : * maintains the specified contract including all protocol specific tolerances 98 : * and therefore clients can rely on common semantics of this type. This makes 99 : * times coming from different hardware peripherals and even from different 100 : * network nodes comparable within well-defined limits and therefore net_time_t 101 : * is the ideal intermediate building block for timed network protocols. 102 : */ 103 1 : typedef int64_t net_time_t; 104 : 105 : /** The largest positive time value that can be represented by net_time_t */ 106 1 : #define NET_TIME_MAX INT64_MAX 107 : 108 : /** The smallest negative time value that can be represented by net_time_t */ 109 1 : #define NET_TIME_MIN INT64_MIN 110 : 111 : /** The largest positive number of seconds that can be safely represented by net_time_t */ 112 1 : #define NET_TIME_SEC_MAX (NET_TIME_MAX / NSEC_PER_SEC) 113 : 114 : /** The smallest negative number of seconds that can be safely represented by net_time_t */ 115 1 : #define NET_TIME_SEC_MIN (NET_TIME_MIN / NSEC_PER_SEC) 116 : 117 : #ifdef __cplusplus 118 : } 119 : #endif 120 : 121 : /** 122 : * @} 123 : */ 124 : 125 : #endif /* ZEPHYR_INCLUDE_NET_NET_TIME_H_ */
