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Occasional incorrect time returned by NTP

Discussion in 'Programming/Internet' started by techkilljoy, Oct 8, 2018.

  1. techkilljoy

    techkilljoy Guest

    I have an Uno with CC3000 wifi shield and am trying to use the sntp.h library to get NTP time. I have been experimenting with a modified version of the ntpTest code from the library which fetches the time every minute. In the serial monitor I get the correct time MOST of the time. However at random intervals, the time will display 3 hours and 14 minutes ahead of the current MST time.

    the SNTP client constructor looks like this:

    sntp mysntp = sntp(NULL,"time.nist.gov", (short)(-7 * 60),(short)(-7 * 60), true);

    The time will display correctly for two to ten minutes and then display one of the erroneous times once then revert to correct time.

    EDIT Here is the pared down code from the Adafruit CC3000 WIFI shield ntpTest example. Note that the only reason I was getting the time so often was just teaching myself how it worked and I noticed this odd behavior. My intent was not to make an application that would, in the end, access NTP servers more than once per day.

    This is an example for the Adafruit CC3000 Wifi Breakout & Shield

    Designed specifically to work with the Adafruit WiFi products:
    ----> https://www.adafruit.com/products/1469

    Adafruit invests time and resources providing this open source code,
    please support Adafruit and open-source hardware by purchasing
    products from Adafruit!

    Written by Kevin Townsend & Limor Fried & Rick Lesniak for Adafruit Industries.
    BSD license, all text above must be included in any redistribution


    This example does a test of the SNTP (Simple Network Time Protocol) client:
    * Initialization
    * SSID Scan
    * AP connection
    * DHCP printout
    * SNTP time synchronization
    * Extract and print current time and date information


    #include <Adafruit_CC3000.h>
    #include <ccspi.h>
    #include <SPI.h>
    //#include "utility/NetTime.h"
    #include <string.h>
    #include "utility/debug.h"
    #include "sntp.h"

    // These are the interrupt and control pins
    #define ADAFRUIT_CC3000_IRQ 3 // MUST be an interrupt pin!
    // These can be any two pins
    #define ADAFRUIT_CC3000_VBAT 5
    #define ADAFRUIT_CC3000_CS 10
    // Use hardware SPI for the remaining pins
    // On an UNO, SCK = 13, MISO = 12, and MOSI = 11
    Adafruit_CC3000 cc3000 = Adafruit_CC3000(ADAFRUIT_CC3000_CS, ADAFRUIT_CC3000_IRQ, ADAFRUIT_CC3000_VBAT,
    SPI_CLOCK_DIVIDER); // you can change this clock speed but DI

    #define WLAN_SSID "CompsciWifi" // cannot be longer than 32 characters!
    #define WLAN_PASS "005276DA"

    //Arguments to SNTP client constructor:
    // 1 - Primary Network Time Server URL (can be NULL)
    // 2 - Secondary Network Time Server URL (also can be NULL)
    // 3 - Local UTC offset in minutes (US Eastern Time is UTC - 5:00
    // 4 - Local UTC offset in minutes for Daylight Savings Time (US Eastern DST is UTC - 4:00
    // 5 - Enable Daylight Savings Time adjustment (not implemented yet)
    //sntp mysntp = sntp(NULL, "time.nist.gov", (short)(-7 * 60), (short)(-7 * 60), true);
    sntp mysntp = sntp(NULL, "time-a.timefreq.bldrdoc.gov", (short)(-7 * 60), (short)(-7 * 60), true);

    // Type SNTP_Timestamp is 64-bit NTP time. High-order 32-bits is seconds since 1/1/1900
    // Low order 32-bits is fractional seconds
    SNTP_Timestamp_t now;

    // Type NetTime_t contains NTP time broken out to human-oriented values:
    // uint16_t millis; ///< Milliseconds after the second (0..999)
    // uint8_t sec; ///< Seconds after the minute (0..59)
    // uint8_t min; ///< Minutes after the hour (0..59)
    // uint8_t hour; ///< Hours since midnight (0..23)
    // uint8_t mday; ///< Day of the month (1..31)
    // uint8_t mon; ///< Months since January (0..11)
    // uint16_t year; ///< Year.
    // uint8_t wday; ///< Days since Sunday (0..6)
    // uint8_t yday; ///< Days since January 1 (0..365)
    // bool isdst; ///< Daylight savings time flag, currently not supported
    NetTime_t timeExtract;

    #define pF(string_pointer) (reinterpret_cast<const __FlashStringHelper *>(pgm_read_word(string_pointer)))

    const prog_char janStr[] PROGMEM = "January";
    const prog_char febStr[] PROGMEM = "February";
    const prog_char marStr[] PROGMEM = "March";
    const prog_char aprStr[] PROGMEM = "April";
    const prog_char mayStr[] PROGMEM = "May";
    const prog_char junStr[] PROGMEM = "June";
    const prog_char julStr[] PROGMEM = "July";
    const prog_char augStr[] PROGMEM = "August";
    const prog_char sepStr[] PROGMEM = "September";
    const prog_char octStr[] PROGMEM = "October";
    const prog_char novStr[] PROGMEM = "November";
    const prog_char decStr[] PROGMEM = "December";

    PROGMEM const char* const monthStrs[] = { janStr, febStr, marStr, aprStr, mayStr, junStr,
    julStr, augStr, sepStr, octStr, novStr, decStr};

    const prog_char sunStr[] PROGMEM = "Sunday";
    const prog_char monStr[] PROGMEM = "Monday";
    const prog_char tueStr[] PROGMEM = "Tuesday";
    const prog_char wedStr[] PROGMEM = "Wednesday";
    const prog_char thuStr[] PROGMEM = "Thursday";
    const prog_char friStr[] PROGMEM = "Friday";
    const prog_char satStr[] PROGMEM = "Saturday";

    PROGMEM const char* const dayStrs[] = { sunStr, monStr, tueStr, wedStr,
    thuStr, friStr, satStr};

    @brief Sets up the HW and the CC3000 module (called automatically
    on startup)
    void setup(void)
    Serial.println(F("Hello, CC3000!\n"));

    //Serial.print("Free RAM: "); Serial.println(getFreeRam(), DEC);

    /* Initialise the module */
    Serial.println(F("\nInitialising the CC3000 ..."));
    if (!cc3000.begin())
    Serial.println(F("Unable to initialise the CC3000! Check your wiring?"));

    /* Optional: Update the Mac Address to a known value */
    uint8_t macAddress[6] = { 0x08, 0x00, 0x28, 0x01, 0x79, 0xB7 };
    if (!cc3000.setMacAddress(macAddress))
    Serial.println(F("Failed trying to update the MAC address"));

    /* Delete any old connection data on the module */
    Serial.println(F("\nDeleting old connection profiles"));
    if (!cc3000.deleteProfiles()) {

    /* Attempt to connect to an access point */
    char *ssid = WLAN_SSID; /* Max 32 chars */
    Serial.print(F("\nAttempting to connect to ")); Serial.println(ssid);

    /* NOTE: Secure connections are not available in 'Tiny' mode! */
    if (!cc3000.connectToAP(WLAN_SSID, WLAN_PASS, WLAN_SECURITY)) {


    /* Wait for DHCP to complete */
    Serial.println(F("Request DHCP"));
    while (!cc3000.checkDHCP())
    delay(100); // ToDo: Insert a DHCP timeout!

    if (mysntp.UpdateNTPTime())
    Serial.println(F("Current local time is:"));
    mysntp.ExtractNTPTime(mysntp.NTPGetTime(&now, true), &timeExtract);*/

    /*Serial.print(timeExtract.hour); Serial.print(F(":")); Serial.print(timeExtract.min); Serial.print(F(":"));Serial.print(timeExtract.sec); Serial.print(F("."));Serial.println(timeExtract.millis);
    Serial.print(pF(&dayStrs[timeExtract.wday])); Serial.print(F(", ")); Serial.print(pF(&monthStrs[timeExtract.mon])); Serial.print(F(" ")); Serial.print(timeExtract.mday); Serial.print(F(", "));Serial.println(timeExtract.year);
    Serial.println(timeExtract.yday + 1);

    /* You need to make sure to clean up after yourself or the CC3000 can freak out */
    /* the next time you try to connect ... */
    /*Serial.println(F("\n\nClosing the connection"));
    cc3000.disconnect(); */

    mysntp.ExtractNTPTime(mysntp.NTPGetTime(&now, true), &timeExtract);
    Serial.print(pF(&dayStrs[timeExtract.wday])); Serial.print(F(", ")); Serial.print(pF(&monthStrs[timeExtract.mon])); Serial.print(F(" ")); Serial.print(timeExtract.mday); Serial.print(F(", "));Serial.println(timeExtract.year);

    void loop(void)
    mysntp.ExtractNTPTime(mysntp.NTPGetTime(&now, true), &timeExtract);
    Serial.print(timeExtract.hour); Serial.print(F(":")); Serial.print(timeExtract.min);


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