Unlocking Accurate Time Synchronization with PTM and TGP on Intel Hardware

Table of Contents

1. Introduction
2. Overview of PTM and TGP
3. Importance of Precisely Synchronized Time
4. Challenges in Time Synchronization
5. How 1588 Achieves Accuracy
6. Introduction to PTM
   • What is PTM?
   • PTM in PCIE Standard
   • Hardware Protocol of PTM
7. Benefits and Use of PTM
8. Using PTM for CPU Time and System Time Synchronization
9. Accuracy of PTM in Different Scenarios
10. Using PTM with POSIX Clock G Time Calls
11. Ground Truth Verification with TGP
12. How TGP Ensures Time Synchronization Accuracy
13. Current Availability of Silicon, Firmware, and Software Support for PTM and TGP
14. Steps for Deployment and Usage of PTM and TGP
    • Steps for OEMs and ODMs
    • Steps for Vendors
    • Steps for End Users
15. Conclusion

Introduction

In today's interconnected world, precise time synchronization is crucial for various applications, including distributed databases, manufacturing, and even self-driving cars. However, achieving accurate time synchronization can be challenging, especially when it comes to transferring time from the Ethernet hardware to the running CPU. To address this issue, two important technologies come into play: PTM (Precision Time Measurement) and TGP (True Ground Truth Verification). In this article, we will delve into the details of PTM and TGP, their significance, and how they enable precise time synchronization. We will also discuss the availability of silicon, firmware, and software support for PTM and TGP, as well as the steps for deploying and using these technologies.

Overview of PTM and TGP

PTM, or Precision Time Measurement, is an optional feature of the PCIE (Peripheral Component Interconnect Express) standard. It is included in the latest client and zone processors, as well as many Ethernet adapters. PTM addresses the challenge of accurately transferring time from the Ethernet hardware to the CPU. It captures snapshots of the PTP (Precision Time Protocol) time and the system time, allowing for a simple subtraction to determine the difference between CPU time and the time on the NIC (Network Interface Card). This enables the discipline of time accessed by CPU applications.

TGP, or True Ground Truth Verification, is used to ensure accurate time synchronization by comparing the pulse per Second from the server's system clock and the pulse per second from the NIC. This comparison can be done using an oscilloscope or logic analyzer, providing a reference for verifying the accuracy of the synchronized time.

Importance of Precisely Synchronized Time

Precisely synchronized time is crucial for a wide range of applications. For example, in distributed databases, accurate time synchronization ensures consistency and reliability in data replication across multiple nodes. In manufacturing, synchronized time enables precise coordination of processes and ensures smooth operation. Even self-driving cars rely on synchronized time for various tasks, such as sensor Fusion and decision-making. In all these applications, the software consumes time and requires access to a shared common sense of time for Scheduling and ordering. Thus, the accurate and precise synchronization of time is of utmost importance.

Challenges in Time Synchronization

Although the Precision Time Protocol (PTP) achieves excellent accuracy using the Ethernet hardware and packets, transferring time from the Ethernet hardware to the running CPU can introduce inaccuracies. The jitter of the operating system, software, and traffic congestion can cause significant errors compared to state-of-the-art PTP or other synchronization protocols. These inaccuracies can range from hundreds to thousands of nanoseconds. This poses a challenge for achieving precise time synchronization in various applications.

How 1588 Achieves Accuracy

1588 is a protocol that achieves accuracy in time synchronization by utilizing the Ethernet hardware and packets. It provides synchronization to a time of authority and ensures that software can Consume time for various purposes. However, transferring time from the Ethernet hardware to the running CPU can introduce inaccuracies and errors due to various factors. This is where PTM comes into play.

Introduction to PTM

What is PTM?

PTM, or Precision Time Measurement, is a hardware protocol that is part of the PCIE standard. It enables the capture of snapshots of the PTP time and system time, allowing for accurate time transfer from the Ethernet hardware to the CPU. PTM is included in the most recent client and zone processors, as well as many Ethernet adapters.

PTM in PCIE Standard

PTM is an optional feature of the PCIE standard. It runs inband over PCIE and simultaneously captures the snapshots of the PTP time and system time. By utilizing the PCIE interface and hardware, PTM provides a reliable and accurate means of transferring time to the CPU.

Hardware Protocol of PTM

PTM utilizes the hardware protocol of the PCIE standard to transfer time from the Ethernet hardware to the running CPU. This hardware-based process minimizes inaccuracies caused by jitter, OS software, and traffic congestion. With PTM, the CPU time and the time on the NIC can be accurately synchronized, allowing for precise time access by CPU applications.

Benefits and Use of PTM

PTM offers several benefits in achieving accurate time synchronization. By capturing snapshots of the PTP time and system time, PTM minimizes inaccuracies and errors that can be introduced during time transfer. It provides a cross-timestamp that can be used to calculate the difference between CPU time and NIC time. This enables the discipline of time accessed by CPU applications, ensuring accurate scheduling and ordering.

The use of PTM is not limited to specific applications or industries. It can be utilized in any Scenario where precise and synchronized time is required. Whether it's distributed databases, manufacturing processes, or self-driving cars, PTM can play a crucial role in achieving accurate time synchronization.

Using PTM for CPU Time and System Time Synchronization

With PTM enabled, the system can bring accurate time into the NIC, which in turn brings accurate time into the CPU and the entire system. This allows applications to access precise time through POSIX (Portable Operating System Interface) clock G time calls, such as clock real time. The beauty of PTM is that as long as the system is enabled with PTM, application programmers can benefit from precise timing without additional software interventions.

By using standard POSIX clock G time calls, applications can easily access the disciplined time provided by PTM. This simplifies the process of using accurate time in various applications and reduces the need for custom time synchronization solutions.

Accuracy of PTM in Different Scenarios

The accuracy of PTM can vary depending on system load and other factors that can induce inaccuracies. In scenarios without PTM, where time transfer relies on software-based methods, significant errors can occur, ranging from hundreds to thousands of nanoseconds. However, with PTM, both idle and loaded scenarios can achieve errors similar to state-of-the-art PTP distribution, hovering around zero AIS (Absolute Internal Synchronization).

This demonstrates the effectiveness of PTM in achieving accurate time synchronization, even in scenarios with system load and other potential inaccuracies. With PTM, precise timing can be achieved, enabling applications to operate with synchronized and reliable time.

Ground Truth Verification with TGP

To ensure the accuracy of time synchronization, TGP, or True Ground Truth Verification, comes into play. TGP involves comparing the pulse per second from the server's system clock and the pulse per second from the NIC. This comparison can be done using an oscilloscope or logic analyzer, providing a reference for verifying the accuracy of the synchronized time.

TGP serves as a crucial step in ensuring that the time being used by the system is accurate and synchronized with the reference clock. By comparing the pulses per second, any discrepancies can be identified and addressed, improving the overall accuracy of time synchronization.

How TGP Ensures Time Synchronization Accuracy

TGP enables the verification and accuracy of time synchronization by comparing the pulses per second from the server's system clock and the NIC. This comparison helps identify any deviations or errors in the synchronized time. By using an oscilloscope or logic analyzer to analyze the pulse waveforms, the ground truth of the time synchronization can be confirmed.

The availability of TGP provides a reliable and objective means of verifying time synchronization accuracy. It ensures that the time being consumed by the software and applications is precisely synchronized, allowing for consistent and reliable operation.

Current Availability of Silicon, Firmware, and Software Support for PTM and TGP

Both silicon and firmware vendors have started enabling support for PTM and TGP in their products. Intel, for example, has been supporting these technologies since 2020, and many of their recent processors and Ethernet adapters include PTM and TGP support. Firmware vendors, such as AMI (American Megatrends Inc.), have also made efforts to expose PTM and TGP options in their firmware.

Software support for PTM and TGP is also available, particularly in the Linux kernel and related packages like PTP4L and PHC2SYS. Using a new enough version of the Linux kernel and the required software packages, applications can access the benefits of PTM and TGP for accurate time synchronization.

Steps for Deployment and Usage of PTM and TGP

To fully deploy and utilize PTM and TGP, collaboration among hardware manufacturers, firmware vendors, and end-users is necessary. The following steps Outline the actions required by each party:

Steps for OEMs and ODMs

OEMs (Original Equipment Manufacturers) and ODMs (Original Design Manufacturers) play a crucial role in the deployment of PTM and TGP. They need to ensure that PTM and TGP are enabled in their firmware and that the necessary options are exposed for configuration. Additionally, OEMs and ODMs need to make the TGP pins accessible for end-users. This involves collaborating with silicon vendors to support PTM and TGP features in Relevant devices, including PCIe switches.

Steps for Vendors

Vendors, including silicon vendors and firmware vendors, contribute to the availability and support of PTM and TGP. Silicon vendors should enable PTM and TGP features in their hardware, ensuring compatibility with the PCIE standard. Firmware vendors, on the other HAND, need to expose PTM and TGP options in their firmware, allowing end-users to enable and configure these features.

Steps for End Users

End users, such as system administrators and application developers, are responsible for utilizing PTM and TGP in their platforms and applications. They need to ensure they are using supported platforms and PCIe devices that have PTM and TGP support enabled. If their platforms do not have support, they should actively request it from their hardware vendors. By using PTM and TGP effectively, end users can achieve precise and accurate time synchronization in their applications.

Conclusion

The availability of PTM and TGP technologies offers a significant breakthrough in achieving precise and accurate time synchronization. PTM addresses the challenge of transferring time from the Ethernet hardware to the running CPU, ensuring minimal inaccuracies and errors. TGP provides ground truth verification and ensures the accuracy of time synchronization by comparing the pulses per second from the system clock and the NIC.

Although PTM and TGP support are already available in various silicon, firmware, and software products, widespread deployment requires collaboration among OEMs, ODMs, vendors, and end users. By following the steps outlined in this article, the industry can collectively harness the benefits of PTM and TGP for improved time synchronization in a variety of applications.

Note: All product names and trademarks Mentioned are the property of their respective owners.

Highlights

• PTM (Precision Time Measurement) and TGP (True Ground Truth Verification) address the challenge of accurate time synchronization.
• PTM enables the precise transfer of time from the Ethernet hardware to the CPU.
• TGP verifies the accuracy of time synchronization by comparing system clock pulses with NIC pulses.
• Precisely synchronized time is essential for distributed databases, manufacturing, and self-driving cars.
• PTM and TGP provide benefits such as improved accuracy and reliable time access for applications.

Frequently Asked Questions (FAQs)

Q: What is the purpose of PTM and TGP? PTM and TGP aim to achieve precise and accurate time synchronization in various applications. PTM enables the transfer of time from the Ethernet hardware to the CPU, minimizing inaccuracies. TGP verifies the accuracy of time synchronization by comparing system clock pulses with NIC pulses.

Q: Can PTM and TGP be used in any industry or application? Yes, PTM and TGP can be utilized in any scenario where precise time synchronization is required. They are applicable in industries such as distributed databases, manufacturing, and even self-driving cars.

Q: Does PTM require special hardware support? Yes, PTM relies on hardware support and is included in the latest client and zone processors, as well as many Ethernet adapters. It utilizes the PCIE standard for accurate time transfer.

Q: How can end-users deploy PTM and TGP in their systems? End-users should ensure they are using supported platforms and PCIe devices that have PTM and TGP support enabled. If their platforms do not have support, they should request it from their hardware vendors.

Q: What benefits does PTM offer for application developers? PTM provides application developers with easy access to precise timing through standard POSIX clock G time calls. This eliminates the need for custom time synchronization solutions and simplifies the process of using accurate time in applications.

Q: How can TGP be used to verify time synchronization accuracy? TGP compares the pulse per second from the server's system clock with the pulse per second from the NIC. By analyzing the pulse waveforms using an oscilloscope or logic analyzer, the ground truth of time synchronization accuracy can be confirmed.

Resources:

• PTP4L
• PHC2SYS