The PTP Clock Manager for Linux (pcm4l) is designed as a high-performance clock recovery solution for packet-based time/phase/frequency synchronization. The pcm4l software includes the
features required to meet the ITU-T Telecom packet equipment clock recommendations, including a
packet clock state machine. In complex networks with partially unknown packet delays, typical in telecom applications, pcm4l offers patented filter algorithms that help to improve synchronization accuracy with time/phase accuracy of under 1 microsecond and frequency accuracy of under 16 parts-per-billion (ppb). In networks with full IEEE 1588 support that are made up of Boundary Clock (BC) or Transparent Clock (TC) nodes, the pcm4l offers an outlier detection algorithm,
used in conjunction with the Renesas ITU-T G.8273.2 hardware filter, which helps to improve
synchronization accuracy with time/phase accuracy of under 5ns filtered (provisional Class D). These tight requirements dictate the use of timing hardware for the synthesis of the physical clock.
The adaptive servo is implemented in software running on a host processor that controls the PTP
Hardware Clock (PHC). The IEEE 1588 protocol also runs on a host processor but does not need to be colocated with pcm4l (i.e., a different processor). The pcm4l architecture and interfaces makes it ideal for open-source architectures, such as White Box hardware and O-RAN. For more information about the PTP Clock Manager, see the pcm4l product page.

Features
▪ Filters the effects of high Packet Delay Variation
(PDV) per G.8273.4 or G.8263
▪ Calibrates for asymmetry when an external local
time reference is available per G.8273.4 APTS
▪ Software provided as clear C code, ready for Linux
distributions
• Runs on Linux kernel v3.0 and higher, using the
PTP Hardware Clock Infrastructure for clock
control
• Dramatically simplifies software integration and
debugging
▪ Support for IEEE1588-2019 Slave Event
Monitoring channel to allow for a timestamp
interface to an external PTP stack
▪ Full PTP clock state machine per ITU-T G.8275.1
Appendix V and G.8275.2 Appendix IV

Applications
▪ Wireless infrastructure for 4.5G and 5G network
equipment
▪ Phase/time synchronization with full timing support
from the network per ITU-T G.8275.1
• Telecom Boundary Clocks (T-BCs) and Telecom
Time Slave Clocks (T-TSCs) according to ITU-T
G.8273.2 for Full Timing Support (FTS) networks
▪ Phase/time synchronization with assisted or partial
timing support from the network per ITU-T
G.8275.2
• Telecom Boundary Clocks (T-BCs) and Telecom
Time Slave Clocks (T-TSCs) according to ITU-T
G.8273.4 for Assisted Partial Timing Support
(APTS) or Partial Timing Support (PTS)
networks