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+/**
+ * @file
+ * SNTP client options list
+ */
+
+/*
+ * Copyright (c) 2007-2009 Frédéric Bernon, Simon Goldschmidt
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Frédéric Bernon, Simon Goldschmidt
+ *
+ */
+#ifndef LWIP_HDR_APPS_SNTP_OPTS_H
+#define LWIP_HDR_APPS_SNTP_OPTS_H
+
+#include "lwip/opt.h"
+#include "lwip/prot/iana.h"
+
+/**
+ * @defgroup sntp_opts Options
+ * @ingroup sntp
+ * @{
+ */
+
+/** SNTP macro to change system time in seconds
+ * Define SNTP_SET_SYSTEM_TIME_US(sec, us) to set the time in microseconds
+ * instead of this one if you need the additional precision. Alternatively,
+ * define SNTP_SET_SYSTEM_TIME_NTP(sec, frac) in order to work with native
+ * NTP timestamps instead.
+ */
+#if !defined SNTP_SET_SYSTEM_TIME || defined __DOXYGEN__
+#define SNTP_SET_SYSTEM_TIME(sec) LWIP_UNUSED_ARG(sec)
+#endif
+
+/** The maximum number of SNTP servers that can be set */
+#if !defined SNTP_MAX_SERVERS || defined __DOXYGEN__
+#define SNTP_MAX_SERVERS LWIP_DHCP_MAX_NTP_SERVERS
+#endif
+
+/** Set this to 1 to implement the callback function called by dhcp when
+ * NTP servers are received. */
+#if !defined SNTP_GET_SERVERS_FROM_DHCP || defined __DOXYGEN__
+#define SNTP_GET_SERVERS_FROM_DHCP LWIP_DHCP_GET_NTP_SRV
+#endif
+
+/** Set this to 1 to support DNS names (or IP address strings) to set sntp servers
+ * One server address/name can be defined as default if SNTP_SERVER_DNS == 1:
+ * \#define SNTP_SERVER_ADDRESS "pool.ntp.org"
+ */
+#if !defined SNTP_SERVER_DNS || defined __DOXYGEN__
+#define SNTP_SERVER_DNS 0
+#endif
+
+/**
+ * SNTP_DEBUG: Enable debugging for SNTP.
+ */
+#if !defined SNTP_DEBUG || defined __DOXYGEN__
+#define SNTP_DEBUG LWIP_DBG_OFF
+#endif
+
+/** SNTP server port */
+#if !defined SNTP_PORT || defined __DOXYGEN__
+#define SNTP_PORT LWIP_IANA_PORT_SNTP
+#endif
+
+/** Sanity check:
+ * Define this to
+ * - 0 to turn off sanity checks (default; smaller code)
+ * - >= 1 to check address and port of the response packet to ensure the
+ * response comes from the server we sent the request to.
+ * - >= 2 to check returned Originate Timestamp against Transmit Timestamp
+ * sent to the server (to ensure response to older request).
+ * - >= 3 @todo: discard reply if any of the VN, Stratum, or Transmit Timestamp
+ * fields is 0 or the Mode field is not 4 (unicast) or 5 (broadcast).
+ * - >= 4 @todo: to check that the Root Delay and Root Dispersion fields are each
+ * greater than or equal to 0 and less than infinity, where infinity is
+ * currently a cozy number like one second. This check avoids using a
+ * server whose synchronization source has expired for a very long time.
+ */
+#if !defined SNTP_CHECK_RESPONSE || defined __DOXYGEN__
+#define SNTP_CHECK_RESPONSE 0
+#endif
+
+/** Enable round-trip delay compensation.
+ * Compensate for the round-trip delay by calculating the clock offset from
+ * the originate, receive, transmit and destination timestamps, as per RFC.
+ *
+ * The calculation requires compiler support for 64-bit integers. Also, either
+ * SNTP_SET_SYSTEM_TIME_US or SNTP_SET_SYSTEM_TIME_NTP has to be implemented
+ * for setting the system clock with sub-second precision. Likewise, either
+ * SNTP_GET_SYSTEM_TIME or SNTP_GET_SYSTEM_TIME_NTP needs to be implemented
+ * with sub-second precision.
+ *
+ * Although not strictly required, it makes sense to combine this option with
+ * SNTP_CHECK_RESPONSE >= 2 for sanity-checking of the received timestamps.
+ * Also, in order for the round-trip calculation to work, the difference
+ * between the local clock and the NTP server clock must not be larger than
+ * about 34 years. If that limit is exceeded, the implementation will fall back
+ * to setting the clock without compensation. In order to ensure that the local
+ * clock is always within the permitted range for compensation, even at first
+ * try, it may be necessary to store at least the current year in non-volatile
+ * memory.
+ */
+#if !defined SNTP_COMP_ROUNDTRIP || defined __DOXYGEN__
+#define SNTP_COMP_ROUNDTRIP 0
+#endif
+
+/** According to the RFC, this shall be a random delay
+ * between 1 and 5 minutes (in milliseconds) to prevent load peaks.
+ * This can be defined to a random generation function,
+ * which must return the delay in milliseconds as u32_t.
+ * Turned off by default.
+ */
+#if !defined SNTP_STARTUP_DELAY || defined __DOXYGEN__
+#ifdef LWIP_RAND
+#define SNTP_STARTUP_DELAY 1
+#else
+#define SNTP_STARTUP_DELAY 0
+#endif
+#endif
+
+/** If you want the startup delay to be a function, define this
+ * to a function (including the brackets) and define SNTP_STARTUP_DELAY to 1.
+ */
+#if !defined SNTP_STARTUP_DELAY_FUNC || defined __DOXYGEN__
+#define SNTP_STARTUP_DELAY_FUNC (LWIP_RAND() % 5000)
+#endif
+
+/** SNTP receive timeout - in milliseconds
+ * Also used as retry timeout - this shouldn't be too low.
+ * Default is 15 seconds. Must not be beolw 15 seconds by specification (i.e. 15000)
+ */
+#if !defined SNTP_RECV_TIMEOUT || defined __DOXYGEN__
+#define SNTP_RECV_TIMEOUT 15000
+#endif
+
+/** SNTP update delay - in milliseconds
+ * Default is 1 hour. Must not be beolw 60 seconds by specification (i.e. 60000)
+ */
+#if !defined SNTP_UPDATE_DELAY || defined __DOXYGEN__
+#define SNTP_UPDATE_DELAY 3600000
+#endif
+
+/** SNTP macro to get system time, used with SNTP_CHECK_RESPONSE >= 2
+ * to send in request and compare in response. Also used for round-trip
+ * delay compensation if SNTP_COMP_ROUNDTRIP != 0.
+ * Alternatively, define SNTP_GET_SYSTEM_TIME_NTP(sec, frac) in order to
+ * work with native NTP timestamps instead.
+ */
+#if !defined SNTP_GET_SYSTEM_TIME || defined __DOXYGEN__
+#define SNTP_GET_SYSTEM_TIME(sec, us) do { (sec) = 0; (us) = 0; } while(0)
+#endif
+
+/** Default retry timeout (in milliseconds) if the response
+ * received is invalid.
+ * This is doubled with each retry until SNTP_RETRY_TIMEOUT_MAX is reached.
+ */
+#if !defined SNTP_RETRY_TIMEOUT || defined __DOXYGEN__
+#define SNTP_RETRY_TIMEOUT SNTP_RECV_TIMEOUT
+#endif
+
+/** Maximum retry timeout (in milliseconds). */
+#if !defined SNTP_RETRY_TIMEOUT_MAX || defined __DOXYGEN__
+#define SNTP_RETRY_TIMEOUT_MAX (SNTP_RETRY_TIMEOUT * 10)
+#endif
+
+/** Increase retry timeout with every retry sent
+ * Default is on to conform to RFC.
+ */
+#if !defined SNTP_RETRY_TIMEOUT_EXP || defined __DOXYGEN__
+#define SNTP_RETRY_TIMEOUT_EXP 1
+#endif
+
+/** Keep a reachability shift register per server
+ * Default is on to conform to RFC.
+ */
+#if !defined SNTP_MONITOR_SERVER_REACHABILITY || defined __DOXYGEN__
+#define SNTP_MONITOR_SERVER_REACHABILITY 1
+#endif
+
+/**
+ * @}
+ */
+
+#endif /* LWIP_HDR_APPS_SNTP_OPTS_H */