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lwip-contrib-mac/apps/sntp/sntp.c

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/**
* @file
* SNTP client module
*
* This is simple "SNTP" client for the lwIP raw API.
* It is a minimal implementation of SNTPv4 as specified in RFC 4330.
*
* For a list of some public NTP servers, see this link :
* http://support.ntp.org/bin/view/Servers/NTPPoolServers
*
* @todo:
* - set/change servers at runtime
* - complete SNTP_CHECK_RESPONSE checks 3 and 4
* - support broadcast/multicast mode?
*/
/*
* 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: Simon Goldschmidt (lwIP raw API part)
*/
#include "lwip/opt.h"
#include "sntp.h"
#include "lwip/timers.h"
#include "lwip/udp.h"
#include "lwip/dns.h"
#include "lwip/ip_addr.h"
#include "lwip/pbuf.h"
#include <string.h>
#include <time.h>
#if LWIP_UDP
/**
* SNTP_DEBUG: Enable debugging for SNTP.
*/
#ifndef SNTP_DEBUG
#define SNTP_DEBUG LWIP_DBG_OFF
#endif
/** SNTP server port */
#ifndef SNTP_PORT
#define SNTP_PORT 123
#endif
/** Set this to 1 to allow SNTP_SERVER_ADDRESS to be a DNS name */
#ifndef SNTP_SERVER_DNS
#define SNTP_SERVER_DNS 0
#endif
/** Set this to 1 to support more than one server */
#ifndef SNTP_SUPPORT_MULTIPLE_SERVERS
#define SNTP_SUPPORT_MULTIPLE_SERVERS 0
#endif
/** \def SNTP_SERVER_ADDRESS
* \brief SNTP server address:
* - as IPv4 address in "u32_t" format
* - as a DNS name if SNTP_SERVER_DNS is set to 1
* May contain multiple server names (e.g. "pool.ntp.org","second.time.server")
*/
#ifndef SNTP_SERVER_ADDRESS
#if SNTP_SERVER_DNS
#define SNTP_SERVER_ADDRESS "pool.ntp.org"
#else
#define SNTP_SERVER_ADDRESS "213.161.194.93" /* pool.ntp.org */
#endif
#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 LI, 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.
*/
#ifndef SNTP_CHECK_RESPONSE
#define SNTP_CHECK_RESPONSE 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.
*/
#ifndef SNTP_STARTUP_DELAY
#define SNTP_STARTUP_DELAY 0
#endif
/** SNTP receive timeout - in milliseconds
* Also used as retry timeout - this shouldn't be too low.
* Default is 3 seconds.
*/
#ifndef SNTP_RECV_TIMEOUT
#define SNTP_RECV_TIMEOUT 3000
#endif
/** SNTP update delay - in milliseconds
* Default is 1 hour.
*/
#ifndef SNTP_UPDATE_DELAY
#define SNTP_UPDATE_DELAY 3600000
#endif
#if (SNTP_UPDATE_DELAY < 15000) && !SNTP_SUPPRESS_DELAY_CHECK
#error "SNTPv4 RFC 4330 enforces a minimum update time of 15 seconds!"
#endif
/** SNTP macro to change system time and/or the update the RTC clock */
#ifndef SNTP_SET_SYSTEM_TIME
#define SNTP_SET_SYSTEM_TIME(sec) ((void)sec)
#endif
/** SNTP macro to change system time including microseconds */
#ifdef SNTP_SET_SYSTEM_TIME_US
#define SNTP_CALC_TIME_US 1
#define SNTP_RECEIVE_TIME_SIZE 2
#else
#define SNTP_SET_SYSTEM_TIME_US(sec, us)
#define SNTP_CALC_TIME_US 0
#define SNTP_RECEIVE_TIME_SIZE 1
#endif
/** SNTP macro to get system time, used with SNTP_CHECK_RESPONSE >= 2
* to send in request and compare in response.
*/
#ifndef SNTP_GET_SYSTEM_TIME
#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.
*/
#ifndef SNTP_RETRY_TIMEOUT
#define SNTP_RETRY_TIMEOUT SNTP_RECV_TIMEOUT
#endif
/** Maximum retry timeout (in milliseconds). */
#ifndef SNTP_RETRY_TIMEOUT_MAX
#define SNTP_RETRY_TIMEOUT_MAX (SNTP_RETRY_TIMEOUT * 10)
#endif
/** Increase retry timeout with every retry sent
* Default is on to conform to RFC.
*/
#ifndef SNTP_RETRY_TIMEOUT_EXP
#define SNTP_RETRY_TIMEOUT_EXP 1
#endif
/* the various debug levels for this file */
#define SNTP_DEBUG_TRACE (SNTP_DEBUG | LWIP_DBG_TRACE)
#define SNTP_DEBUG_STATE (SNTP_DEBUG | LWIP_DBG_STATE)
#define SNTP_DEBUG_WARN (SNTP_DEBUG | LWIP_DBG_LEVEL_WARNING)
#define SNTP_DEBUG_WARN_STATE (SNTP_DEBUG | LWIP_DBG_LEVEL_WARNING | LWIP_DBG_STATE)
#define SNTP_DEBUG_SERIOUS (SNTP_DEBUG | LWIP_DBG_LEVEL_SERIOUS)
#define SNTP_ERR_KOD 1
/* SNTP protocol defines */
#define SNTP_MSG_LEN 48
#define SNTP_OFFSET_LI_VN_MODE 0
#define SNTP_LI_MASK 0xC0
#define SNTP_LI_NO_WARNING 0x00
#define SNTP_LI_LAST_MINUTE_61_SEC 0x01
#define SNTP_LI_LAST_MINUTE_59_SEC 0x02
#define SNTP_LI_ALARM_CONDITION 0x03 /* (clock not synchronized) */
#define SNTP_VERSION_MASK 0x38
#define SNTP_VERSION (4/* NTP Version 4*/<<3)
#define SNTP_MODE_MASK 0x07
#define SNTP_MODE_CLIENT 0x03
#define SNTP_MODE_SERVER 0x04
#define SNTP_MODE_BROADCAST 0x05
#define SNTP_OFFSET_STRATUM 1
#define SNTP_STRATUM_KOD 0x00
#define SNTP_OFFSET_ORIGINATE_TIME 24
#define SNTP_OFFSET_RECEIVE_TIME 32
#define SNTP_OFFSET_TRANSMIT_TIME 40
/* number of seconds between 1900 and 1970 */
#define DIFF_SEC_1900_1970 (2208988800UL)
/**
* SNTP packet format (without optional fields)
* Timestamps are coded as 64 bits:
* - 32 bits seconds since Jan 01, 1970, 00:00
* - 32 bits seconds fraction (0-padded)
* For future use, if the MSB in the seconds part is set, seconds are based
* on Feb 07, 2036, 06:28:16.
*/
#ifdef PACK_STRUCT_USE_INCLUDES
# include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
struct sntp_msg {
PACK_STRUCT_FIELD(u8_t li_vn_mode);
PACK_STRUCT_FIELD(u8_t stratum);
PACK_STRUCT_FIELD(u8_t poll);
PACK_STRUCT_FIELD(u8_t precision);
PACK_STRUCT_FIELD(u32_t root_delay);
PACK_STRUCT_FIELD(u32_t root_dispersion);
PACK_STRUCT_FIELD(u32_t reference_identifier);
PACK_STRUCT_FIELD(u32_t reference_timestamp[2]);
PACK_STRUCT_FIELD(u32_t originate_timestamp[2]);
PACK_STRUCT_FIELD(u32_t receive_timestamp[2]);
PACK_STRUCT_FIELD(u32_t transmit_timestamp[2]);
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
# include "arch/epstruct.h"
#endif
/* function prototypes */
static void sntp_request(void *arg);
/** The UDP pcb used by the SNTP client */
static struct udp_pcb* sntp_pcb;
/** Addresses of servers */
static char* sntp_server_addresses[] = {SNTP_SERVER_ADDRESS};
#if SNTP_SUPPORT_MULTIPLE_SERVERS
/** The currently used server (initialized to 0) */
static u8_t sntp_current_server;
static u8_t sntp_num_servers = sizeof(sntp_server_addresses)/sizeof(char*);
#else /* SNTP_SUPPORT_MULTIPLE_SERVERS */
#define sntp_current_server 0
#endif /* SNTP_SUPPORT_MULTIPLE_SERVERS */
#if SNTP_RETRY_TIMEOUT_EXP
#define SNTP_RESET_RETRY_TIMEOUT() sntp_retry_timeout = SNTP_RETRY_TIMEOUT
/** Retry time, initialized with SNTP_RETRY_TIMEOUT and doubled with each retry. */
static u32_t sntp_retry_timeout;
#else /* SNTP_RETRY_TIMEOUT_EXP */
#define SNTP_RESET_RETRY_TIMEOUT()
#define sntp_retry_timeout SNTP_RETRY_TIMEOUT
#endif /* SNTP_RETRY_TIMEOUT_EXP */
#if SNTP_CHECK_RESPONSE >= 1
/** Saves the last server address to compare with response */
static ip_addr_t sntp_last_server_address;
#endif /* SNTP_CHECK_RESPONSE >= 1 */
#if SNTP_CHECK_RESPONSE >= 2
/** Saves the last timestamp sent (which is sent back by the server)
* to compare against in response */
static u32_t sntp_last_timestamp_sent[2];
#endif /* SNTP_CHECK_RESPONSE >= 2 */
/**
* SNTP processing of received timestamp
*/
static void
sntp_process(u32_t *receive_timestamp)
{
/* convert SNTP time (1900-based) to unix GMT time (1970-based)
* @todo: if MSB is 1, SNTP time is 2036-based!
*/
time_t t = (ntohl(receive_timestamp[0]) - DIFF_SEC_1900_1970);
#if SNTP_CALC_TIME_US
u32_t us = ntohl(receive_timestamp[1]) / 4295;
SNTP_SET_SYSTEM_TIME_US(t, us);
/* display local time from GMT time */
LWIP_DEBUGF(SNTP_DEBUG_TRACE, ("sntp_process: %s, %"U32_F" us", ctime(&t), us));
#else /* SNTP_CALC_TIME_US */
/* change system time and/or the update the RTC clock */
SNTP_SET_SYSTEM_TIME(t);
/* display local time from GMT time */
LWIP_DEBUGF(SNTP_DEBUG_TRACE, ("sntp_process: %s", ctime(&t)));
#endif /* SNTP_CALC_TIME_US */
}
/**
* Initialize request struct to be sent to server.
*/
static void
sntp_initialize_request(struct sntp_msg *req)
{
memset(req, 0, SNTP_MSG_LEN);
req->li_vn_mode = SNTP_LI_NO_WARNING | SNTP_VERSION | SNTP_MODE_CLIENT;
#if SNTP_CHECK_RESPONSE >= 2
{
u32_t sntp_time_sec, sntp_time_us;
/* fill in transmit timestamp and save it in 'sntp_last_timestamp_sent' */
SNTP_GET_SYSTEM_TIME(sntp_time_sec, sntp_time_us);
sntp_last_timestamp_sent[0] = htonl(sntp_time_sec + DIFF_SEC_1900_1970);
req->transmit_timestamp[0] = sntp_last_timestamp_sent[0];
/* we send/save us instead of fraction to be faster... */
sntp_last_timestamp_sent[1] = htonl(sntp_time_us);
req->transmit_timestamp[1] = sntp_last_timestamp_sent[1];
}
#endif /* SNTP_CHECK_RESPONSE >= 2 */
}
/**
* Retry: send a new request (and increase retry timeout).
*
* @param arg is unused (only necessary to conform to sys_timeout)
*/
static void
sntp_retry(void* arg)
{
LWIP_UNUSED_ARG(arg);
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_retry: Next request will be sent in %"U32_F" ms\n",
sntp_retry_timeout));
/* set up a timer to send a retry and increase the retry delay */
sys_timeout(sntp_retry_timeout, sntp_request, NULL);
#if SNTP_RETRY_TIMEOUT_EXP
{
u32_t new_retry_timeout;
/* increase the timeout for next retry */
new_retry_timeout = sntp_retry_timeout << 1;
/* limit to maximum timeout and prevent overflow */
if ((new_retry_timeout <= SNTP_RETRY_TIMEOUT_MAX) &&
(new_retry_timeout > sntp_retry_timeout)) {
sntp_retry_timeout = new_retry_timeout;
}
}
#endif /* SNTP_RETRY_TIMEOUT_EXP */
}
#if SNTP_SUPPORT_MULTIPLE_SERVERS
/**
* If Kiss-of-Death is received (or another packet parsing error),
* try the next server or retry the current server and increase the retry
* timeout if only one server is available.
*
* @param arg is unused (only necessary to conform to sys_timeout)
*/
static void
sntp_try_next_server(void* arg)
{
LWIP_UNUSED_ARG(arg);
if (sntp_num_servers > 1) {
/* new server: reset retry timeout */
SNTP_RESET_RETRY_TIMEOUT();
sntp_current_server++;
if (sntp_current_server >= sntp_num_servers) {
sntp_current_server = 0;
}
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_try_next_server: Sending request to server %"U16_F"\n",
(u16_t)sntp_current_server));
/* instantly send a request to the next server */
sntp_request(NULL);
} else {
sntp_retry(NULL);
}
}
#else /* SNTP_SUPPORT_MULTIPLE_SERVERS */
/* Always retry on error if only one server is supported */
#define sntp_try_next_server sntp_retry
#endif /* SNTP_SUPPORT_MULTIPLE_SERVERS */
/** UDP recv callback for the sntp pcb */
static void
sntp_recv(void *arg, struct udp_pcb* pcb, struct pbuf *p, ip_addr_t *addr, u16_t port)
{
u8_t mode;
u8_t stratum;
u32_t receive_timestamp[SNTP_RECEIVE_TIME_SIZE];
err_t err;
LWIP_UNUSED_ARG(arg);
LWIP_UNUSED_ARG(pcb);
/* packet received: stop retry timeout */
sys_untimeout(sntp_try_next_server, NULL);
sys_untimeout(sntp_request, NULL);
err = ERR_ARG;
#if SNTP_CHECK_RESPONSE >= 1
/* check server address and port */
if (ip_addr_cmp(addr, &sntp_last_server_address) &&
(port == SNTP_PORT))
#else /* SNTP_CHECK_RESPONSE >= 1 */
LWIP_UNUSED_ARG(addr);
LWIP_UNUSED_ARG(port);
#endif /* SNTP_CHECK_RESPONSE >= 1 */
{
/* process the response */
if (p->tot_len == SNTP_MSG_LEN) {
pbuf_copy_partial(p, &mode, 1, SNTP_OFFSET_LI_VN_MODE);
mode &= SNTP_MODE_MASK;
/* if this is a SNTP response... */
if ((mode == SNTP_MODE_SERVER) ||
(mode == SNTP_MODE_BROADCAST)) {
pbuf_copy_partial(p, &stratum, 1, SNTP_OFFSET_STRATUM);
if (stratum == SNTP_STRATUM_KOD) {
/* Kiss-of-death packet. Use another server or increase UPDATE_DELAY. */
err = SNTP_ERR_KOD;
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_recv: Received Kiss-of-Death\n"));
} else {
#if SNTP_CHECK_RESPONSE >= 2
/* check originate_timetamp against sntp_last_timestamp_sent */
u32_t originate_timestamp[2];
pbuf_copy_partial(p, &originate_timestamp, 8, SNTP_OFFSET_ORIGINATE_TIME);
if ((originate_timestamp[0] != sntp_last_timestamp_sent[0]) ||
(originate_timestamp[1] != sntp_last_timestamp_sent[1]))
{
LWIP_DEBUGF(SNTP_DEBUG_WARN, ("sntp_recv: Invalid originate timestamp in response\n"));
} else
#endif /* SNTP_CHECK_RESPONSE >= 2 */
/* @todo: add code for SNTP_CHECK_RESPONSE >= 3 and >= 4 here */
{
/* correct answer */
err = ERR_OK;
pbuf_copy_partial(p, &receive_timestamp, SNTP_RECEIVE_TIME_SIZE * 4, SNTP_OFFSET_RECEIVE_TIME);
}
}
} else {
LWIP_DEBUGF(SNTP_DEBUG_WARN, ("sntp_recv: Invalid mode in response: %"U16_F"\n", (u16_t)mode));
}
} else {
LWIP_DEBUGF(SNTP_DEBUG_WARN, ("sntp_recv: Invalid packet length: %"U16_F"\n", p->tot_len));
}
}
pbuf_free(p);
if (err == ERR_OK) {
/* Correct response, reset retry timeout */
SNTP_RESET_RETRY_TIMEOUT();
sntp_process(receive_timestamp);
/* Set up timeout for next request */
sys_timeout((u32_t)SNTP_UPDATE_DELAY, sntp_request, NULL);
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_recv: Scheduled next time request: %"U32_F" ms\n",
(u32_t)SNTP_UPDATE_DELAY));
} else if (err == SNTP_ERR_KOD) {
/* Kiss-of-death packet. Use another server or increase UPDATE_DELAY. */
sntp_try_next_server(NULL);
} else {
/* another error, try the same server again */
sntp_retry(NULL);
}
}
/** Actually send an sntp request to a server.
*
* @param server_addr resolved IP address of the SNTP server
*/
static void
sntp_send_request(ip_addr_t *server_addr)
{
struct pbuf* p;
p = pbuf_alloc(PBUF_TRANSPORT, SNTP_MSG_LEN, PBUF_RAM);
if (p != NULL) {
struct sntp_msg *sntpmsg = (struct sntp_msg *)p->payload;
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_send_request: Sending request to server\n"));
/* initialize request message */
sntp_initialize_request(sntpmsg);
/* send request */
udp_sendto(sntp_pcb, p, server_addr, SNTP_PORT);
/* free the pbuf after sending it */
pbuf_free(p);
/* set up receive timeout: try next server or retry on timeout */
sys_timeout((u32_t)SNTP_RECV_TIMEOUT, sntp_try_next_server, NULL);
#if SNTP_CHECK_RESPONSE >= 1
/* save server address to verify it in sntp_recv */
ip_addr_set(&sntp_last_server_address, server_addr);
#endif /* SNTP_CHECK_RESPONSE >= 1 */
} else {
LWIP_DEBUGF(SNTP_DEBUG_SERIOUS, ("sntp_send_request: Out of memory, trying again in %"U32_F" ms\n",
(u32_t)SNTP_RETRY_TIMEOUT));
/* out of memory: set up a timer to send a retry */
sys_timeout((u32_t)SNTP_RETRY_TIMEOUT, sntp_request, NULL);
}
}
#if SNTP_SERVER_DNS
/**
* DNS found callback when using DNS names as server address.
*/
static void
sntp_dns_found(const char* hostname, ip_addr_t *ipaddr, void *arg)
{
LWIP_UNUSED_ARG(hostname);
LWIP_UNUSED_ARG(arg);
if (ipaddr != NULL) {
/* Address resolved, send request */
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_dns_found: Server address resolved, sending request\n"));
sntp_send_request(ipaddr);
} else {
/* DNS resolving failed -> try another server */
LWIP_DEBUGF(SNTP_DEBUG_WARN_STATE, ("sntp_dns_found: Failed to resolve server address resolved, trying next server\n"));
sntp_try_next_server(NULL);
}
}
#endif /* SNTP_SERVER_DNS */
/**
* Send out an sntp request.
*
* @param arg is unused (only necessary to conform to sys_timeout)
*/
static void
sntp_request(void *arg)
{
ip_addr_t sntp_server_address;
err_t err;
LWIP_UNUSED_ARG(arg);
/* initialize SNTP server address */
#if SNTP_SERVER_DNS
err = dns_gethostbyname(sntp_server_addresses[sntp_current_server], &sntp_server_address,
sntp_dns_found, NULL);
if (err == ERR_INPROGRESS) {
/* DNS request sent, wait for sntp_dns_found being called */
LWIP_DEBUGF(SNTP_DEBUG_STATE, ("sntp_request: Waiting for server address to be resolved.\n"));
return;
}
#else /* SNTP_SERVER_DNS */
err = ipaddr_aton(sntp_server_addresses[sntp_current_server], &sntp_server_address)
? ERR_OK : ERR_ARG;
#endif /* SNTP_SERVER_DNS */
if (err == ERR_OK) {
sntp_send_request(&sntp_server_address);
} else {
/* address conversion failed, try another server */
LWIP_DEBUGF(SNTP_DEBUG_WARN_STATE, ("sntp_request: Invalid server address, trying next server.\n"));
sys_timeout((u32_t)SNTP_RETRY_TIMEOUT, sntp_try_next_server, NULL);
}
}
/**
* Initialize this module.
* Send out request instantly or after SNTP_STARTUP_DELAY.
*/
void
sntp_init(void)
{
if (sntp_pcb == NULL) {
SNTP_RESET_RETRY_TIMEOUT();
sntp_pcb = udp_new();
LWIP_ASSERT("Failed to allocate udp pcb for sntp client", sntp_pcb != NULL);
if (sntp_pcb != NULL) {
udp_recv(sntp_pcb, sntp_recv, NULL);
#if SNTP_STARTUP_DELAY
sys_timeout((u32_t)SNTP_STARTUP_DELAY, sntp_request, NULL);
#else
sntp_request(NULL);
#endif
}
}
}
/**
* Stop this module.
*/
void
sntp_stop(void)
{
if (sntp_pcb != NULL) {
sys_untimeout(sntp_request, NULL);
udp_remove(sntp_pcb);
sntp_pcb = NULL;
}
}
#endif /* LWIP_UDP */
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