I just ported some NTP stuff from an old program.
Querying an NTP server is surprisingly easy: just send it a 48 byte UDP packet with the first byte = 27 and the rest of them 0.
The NTP server should return your 48 byte packet updated with the last 16 bytes set to two 64-bit timestamps, being when it (i) received your request and (ii) soon-after sent its response.
My code "returns" 4 timestamps NTPTimeStamp(1) thru NTPTimeStamp(4), matching T1..T4 of this command-line utility:
https://kb.meinbergglobal.com/kb/public_utilitiy_programs/ntptest_-_check_ntp_server
except that my timestamps are in Java ticks (ms since 1970) for easy use with DateTime formatting etc.
I did this example with B4J but the same principles work in B4A (as in: I've run similar code successfully there too).
Querying an NTP server is surprisingly easy: just send it a 48 byte UDP packet with the first byte = 27 and the rest of them 0.
The NTP server should return your 48 byte packet updated with the last 16 bytes set to two 64-bit timestamps, being when it (i) received your request and (ii) soon-after sent its response.
My code "returns" 4 timestamps NTPTimeStamp(1) thru NTPTimeStamp(4), matching T1..T4 of this command-line utility:
https://kb.meinbergglobal.com/kb/public_utilitiy_programs/ntptest_-_check_ntp_server
except that my timestamps are in Java ticks (ms since 1970) for easy use with DateTime formatting etc.
I did this example with B4J but the same principles work in B4A (as in: I've run similar code successfully there too).
B4X:
#Region Project Attributes
#MainFormWidth: 300
#MainFormHeight: 300
#End Region
Sub Process_Globals
Private fx As JFX
Private MainForm As Form
Private xui As XUI
Private Button1 As B4XView
Dim UDPSocket1 As UDPSocket
Dim NTPPort As Int = 123
Dim NTP1970 As Long = ((1970 - 1900) * 365 + 17).As(Long) * 86400
Dim NTPTimeStamp(5) As Double 'to match T1..T4 of Meinberg NTPTEST utility
End Sub
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
MainForm.RootPane.LoadLayout("Layout1")
MainForm.Show
UDPSocket1.Initialize("UDP", NTPPort, 8000)
End Sub
Sub SendNtpRequest(NTPServerName As String)
Dim data(48) As Byte
data(0) = 27
Dim Packet As UDPPacket
Packet.Initialize(data, NTPServerName, NTPPort)
NTPTimeStamp(4) = 0 'so can tell if received reply
NTPTimeStamp(1) = DateTime.Now
UDPSocket1.Send(Packet)
End Sub
Sub UDP_PacketArrived (Packet As UDPPacket)
If Packet.Length < 48 Then Return
NTPTimeStamp(4) = DateTime.Now
Dim StartFrom As Int = Packet.Offset + 32
For ServerTimeStamp = 2 To 3
Dim Temp As Long = 0
For I = StartFrom To StartFrom + 6 '7 bytes (32 bits seconds + 24 bits fraction)
Temp = Bit.ShiftLeftLong(Temp, 8) + Bit.And(Packet.Data(I), 0xFF)
Next
Dim NTPSeconds As Double = Temp / 0x1000000 'shift binary point 24 bits left
Dim JavaTicks As Double = (NTPSeconds - NTP1970) * 1000
NTPTimeStamp(ServerTimeStamp) = JavaTicks
StartFrom = StartFrom + 8 'next 64-bit timestamp
Next
End Sub
Sub Button1_Click
Dim NTPServerName As String = "au.pool.ntp.org"
SendNtpRequest(NTPServerName)
Sleep(2000)
If NTPTimeStamp(4) = 0 Then
Log("No reply from " & NTPServerName)
Return
End If
Log(NTPServerName)
For I = 1 To 4
Log("T" & I & " = " & NumberFormat2(NTPTimeStamp(I), 1, 3, 3, False))
Next
Dim LocalTimeMiddle As Double = (NTPTimeStamp(1) + NTPTimeStamp(4)) / 2
Dim ServerTimeMiddle As Double= (NTPTimeStamp(2) + NTPTimeStamp(3)) / 2
Dim DeviceToNTPOffset As Double = ServerTimeMiddle - LocalTimeMiddle
If DeviceToNTPOffset < 0 Then
Dim Direction As String = "ahead of"
Else
Dim Direction As String = "behind"
End If
Log( _
"Device clock is " & _
NumberFormat2(Abs(DeviceToNTPOffset), 1, 1, 1, False) & _
" ms " & Direction & " NTP server time (roundtrip " & _
NumberFormat2(NTPTimeStamp(4) - NTPTimeStamp(1), 1, 1, 1, False) & _
" ms)" _
)
DateTime.TimeFormat = "hh:mm:ss.SSS"
Dim N As Long = DateTime.Now
Log("Device clock = " & DateTime.Time(N))
Log("NTP clock = " & DateTime.Time(N + DeviceToNTPOffset))
End Sub
Last edited:
