Designers Can Synchronize Clocks Without External Oscillators Thanks to IEEE 158...

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Designers Can Synchronize Clocks Without External Oscillators Thanks to IEEE 1588

December 12, 2020 by Antonio Anzaldua Jr.

Updates to the IEEE 1588 standard protocol map out a low-cost method for synchronizing distributed clocks.

The Institute of Electrical and Electronics Engineers (IEEE) has approved a standard protocol to synchronize independent clocks running on a shared network. This will, in hopes, allow designers to perform accurate and precise measurements on control systems across a broad range of applications.

Designers that are involved in test and measurement for industrial automation or mobile communications can face challenges around maintaining synchronized data collection from multiple devices. Modern electronics that are separated by distance or have frequency rates varying over time and temperature will cause propagation delays that lead to unsynchronized timing clocks.

IEEE has established a protocol that allows devices to periodically exchange data while adjusting their local timing sources to match each other—regardless of distance, temperature, and physical factors.  

History of IEEE 1588

In 2002, the protocol standard IEEE 1588 was approved to help designers avoid faults in frequency sources that vary in rates, which would desynchronize devices’ clocks. It is a cost-effective solution for local systems requiring accuracies beyond network time protocol (NTP) and global positioning system (GPS); these systems would require external NTP and GPS receivers at each node, adding to the bill of materials.

The communication mechanism of IEEE 1588
The communication mechanism of IEEE 1588. Image used courtesy of Wikimedia Commons

Six New Amendments

The IEEE 1588 has released six amendments to prior protocols. The additions aim to ensure accuracy and precision in the sub-microsecond range—and in devices with minimal network and local computing resources:

  • 1st amendment: Enhancements for best master clock algorithms (BMCA) 
  • 2nd amendment: Addition of precision time protocol (PTP)
  • 3rd amendment: Clarification of terminology 
  • 4th amendment: Guidelines for selecting and operating a key management system
  • 5th amendment: MIB and YANG data models
  • 6th amendment: Enhancements for latency and/or asymmetry calibration 
Illustration of the PTP protocol
Illustration of the PTP protocol. Image used courtesy of Silicon Labs

Each amendment guides developers on establishing the collection and transfer of data through synchronized clocks of different precision, resolution, and stability capabilities. The foundation of the IEEE 1588 is the PTP, a protocol that synchronizes clocks based on a simple shared network that can be achieved via ethernet connections. 

The protocol utilizes the BMCA, an algorithm that compares data between each clock in the shared network to identify the clock of the highest quality and deems it the grandmaster. The grandmaster sets the tone by choosing a frequency rate that all other clocks will adjust to match, causing synchronization that lets data transfer smoothly.

If the grandmaster is removed, altered, or exhibits sub-par quality, the BMCA provides a way for the remaining clocks to determine the next in line clock to lead as the grandmaster.

Ways of Implementing IEEE 1588 Protocol 

It is very common for devices to have external oscillators in order to maintain synchronized clocks. The problem with having independent devices rely on dedicated oscillators is that each oscillator could be facing different operating conditions that impact the clocks’ ability to stay synchronized.

There are various developers implementing IEEE 1588 standard protocol into their devices to make this easier for designers.

ADI's New Processor Implements IEEE 1588

Analog Devices (ADI), for instance, has rolled out a low-power Blackfin processor with advanced embedded connectivity. This 32-bit core processor is driven by a 3-phase pulse-width modulator (PWM) generation unit that implements the IEEE 1588 standard protocol, giving design engineers the freedom to choose any physical layer.

ADI also says its ADSP-BF518 offers firmware protection along with performance diagnostic software to quicken the debugging process. Image used courtesy of Analog Devices

Embedded-system designers may experience specific challenges with systems that have voice over internet protocol (VoIP), the option to place phone calls over an internet connection. The hurdle comes with finding the right processing unit that can implement a low channel count VoIP solution, yet be able to handle video, music, imaging, and system controls.

In most cases, the designer will need two separate processing cores. ADI claims its ADSP-BF518 allows voice and video signal processing concurrent through one core processor. 

SiLabs' IEEE 1588 Modules

Silicon Labs (SiLabs) has also kept the IEEE 1588 protocol in mind with its recent ClockBuilder Pro software tool, a step-by-step tool that gives designers the power to customize clock parameters for generators, jitter attenuators, buffers, and oscillator products. The device provides real-time feedback on the overall performance of the clocks in the network. SiLabs also says it smooths communication with external evaluation boards. 

SiLabs’ M88-256
SiLabs’ M88-256 is a high-precision gateway clock that has an operating temperature range of -40 to +85 degrees celsius. Image used courtesy of Silicon Labs

SiLabs also offers IEEE 1588 modules that provide clock synchronization via single and dual ports of an ethernet connection. The M88-256 implements the IEEE 1588 protocol with 256 controllable clocks that will identify and synchronize to a grandmaster.

A Low-Cost Way to Synchronize Clocks

The IEEE 1588 standard specifies requirements for mapping out a low-cost method for synchronizing distributed clocks.

Even though hardware support is not well defined in the protocol, there are various developers manufacturing hardware-assisted devices that abide by the standard. Designers will have more options to achieve the highest level of synchronization precision in the coming years. 

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