R31DS0087EU0101 Rev.1.01

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Sep.28.21

pcm4l Datasheet

The PCM supports various means to stabilize the frequency and/or time of the local PTP clock. This can be by

physical layer assistance (i.e., SyncE) as used by the G.8275.1 Profile (and optional for the G.8275.2 Profile) or

local GNSS assistance as used by the G.8275.2 Profile for APTS (and optionally being consider with G.8275.1

Profile as well).

The Renesas software simplifies the complex process of integrating packet-based timing for network

synchronization into a larger system. Separating the 1588 protocol from the clock recovery allows the user to use

readily available PTP stacks for the protocol, to use the existing Linux kernel socket options and PTP clock

infrastructure for time stamp and clock correction routing within the kernel, and to use different vendors (and

drivers) for each of the 1588 system components.

An example of such a PTP stack is Linux PTP, or ptp4l. The ptp4l software already implements the IEEE 1588-

2008 standard, including supporting some industry 1588 Profiles, and uses the Linux kernel PTP infrastructure to

access hardware for retrieving local hardware (HW) timestamps and clock control. Many CPU/SoC vendors

already provide kernel driver support for the HW-based PTP timestamper, and may even provide a driver for the

PTP Hardware Clock (PHC) to control its PTP clock. The ptp4l software also supports a simple Proportional-

Integral (PI) filter along with a servo and stage machine. However, this PI-filter was not designed to support the

PDV that could be experienced on PTP timing packets when using the ITU-T G.8265.1 or G.8275.2 Profiles. A

much more sophisticated adaptive algorithm would be needed to do packet selection and filtering. This is where

the Renesas PCM fits in.

As of LinuxPTP v3.0, a new Slave Event Monitoring channel, per IEEE 1588-2019, was added to ptp4l to allow for

an external filter/servo to take control of the PTP clock. The Renesas pcm4l software also supports the Slave

Event Monitoring channel as part of its PTP Stack Adaptor, and is discussed further in the following sections.

Looking at the pcm4l directory structure in Figure 3, the core software (idtCore\) comprises four component

modules: Reference Tracker(s), Reference Tracker Supervisor, APTS Supervisor, and Local PTP Clock State

Machine. Customers are not expected to modify the core software component modules. The PCM software

communicates to the PTP stack via the PTP Stack Adaptor (ptpStack\). The following sections provide more

details.

The system software component (idtSystem) contains all the adaptors and adaption code. This should not be

modified, as they have already been updated for Linux.