Added initial version of the ptp docs.

Author: antongit

reference/best-practice/ptp.md

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+# Synchronizing machines to the High Precision Clock
+
+Starting from Windows10 (build) window's System Time can be synchronized to a High Precision Time Sourse that uses [PTP](https://de.wikipedia.org/wiki/Precision_Time_Protocol) (Precision Time Protocol). PTP is more precise that NTP (Network Time Protocol), which is used normally by Windows to keep its time in sync.
+
+## Overview:
+
+There should be at least one PTP Source in your LAN Network. In case there are many, they agee upon each other who the `Grandmaster` is. Clients sync their time to one of the sources.
+
+## Configuration of a client
+
+Configuring PTP on the system takes several steps:
+
+1. To check if your system has this dll: `C:\Windows\System32\ptpprov.dll`.
+1. Check if one of your LAN cards (Wi-Fi won't work) support PTP: 
+    1. Navigate to `View Network Connections > Right Click > Properties > Configure > Advanced`
+    1. Look for `PTP Protocol Timestamp` and enable it. Some network cards doesn't support it at all.
+    1. If the system has several cards, the one with PTP Enabled should be assigned as preffered one, in order to be picked by a time service: in the `Properties` of the Network Adapter: `Internet Protocol Version 4 (TCP/IPv4) > Properties > Advanced` turn off `Automatic metric` and set it to a value, smaller than for the other cards. 
+1. Run registry file (link), it sets several keys:
+    1. A key `PtpClient` (Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\w32time\TimeProviders\PtpClient) with some subkeys is added, as described [here](). **Note**, you have to replace PtpMasters with the IP(s) of your ptp time providers.
+    2. Some subkeys under a `Config` key (Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\w32time\TimeProviders\PtpClient) are updated according to [Configuring Systems for High Accuracy](https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/configuring-systems-for-high-accuracy).
+    1. Ntp providers will be disabled (your normal default time server), only PtpClient remains enabled.
+1. Enable Inbound and Outbound UDP Ports 219,220 in Windows Firewall. These are used by the PTP protocol.
+
+When the configuration is ready:
+
+1. Start `Command Line` as Adminitrator
+1. Restart the time service: `net stop w32time`, `net start w32time`.
+1. Make sure that the service starts automatically on start (check `System Services`).
+1. Run `w32tm /query /configuration`, you should see PtPClient in the list.
+1. Run `w32tm /query /status /verbose` to see the status of the sync. If `Source` says `Local CMOS Clock` the system still doesn't sync to the PTP.
+
+It takes some time until the client and server done their agreements, after that periodically checking `w32tm /query /status /verbose` will give you hints how many seconds ago the system was synced etc.
+
+## Configuration of a Server (Ptp Time Source)
+
+Although there are special hardware PTP Sources, PTP Source Service can run from on a simple Raspberry Pi 5 (Network Card on the earlier versions doesn't support PTP). And if a real high precision time is needed, a GPS receiver could be added to the Raspberry Pi.
+
+These articles describe how to setup and run PTP Service on Linux:
+
+- [Nanosecond accurate PTP server](https://austinsnerdythings.com/2025/02/18/nanosecond-accurate-ptp-server-grandmaster-and-client-tutorial-for-raspberry-pi/)
+- [Windows Subsystem for Linux for testing Windows 10 PTP Client](https://techcommunity.microsoft.com/blog/networkingblog/windows-subsystem-for-linux-for-testing-windows-10-ptp-client/389181)
+
+
+## Unicast and Multicast scenarios
+
+...