|
RTS IEEE 1588 Network Stack |
 User Documentation (2.81 MB)
The RTS IEEE 1588 Master and Slave software stack incorporates the full specification and functionality of the Precision Clock Synchronization Protocol for Networked Measurement and Control Systems (PTP).
Through PTP, multiple devices are automatically synchronized with the most accurate clock found in a packet-based network – typically Ethernet. The RTS protocol stack automatically determines the most accurate clock, otherwise known as the Grand Master Clock. During operation and after initial synchronization, the PTP real-time clocks are constantly adjusted by exchanging timing messages.
The RTS implementation uses statistical techniques to further reduce residual fluctuations. Because the RTS IEEE 1588 protocol stack supports the PTP hot-pluggable functionality requirement, devices may join or leave the network at any time.
The software is simple, administration free and requires minimal resources of host components or networks.
In the past, all implementations of the IEEE 1588 protocol requiring high accuracy also required hardware-implemented timestamping.
Typically hardware-implemented timestamping adds extra non-standard components and costs. The RTS implementation achieves accuracies of up to ± five microseconds using only common network interfaces, and does not require hardware-implemented timestamping.
The RTS IEEE 1588 Protocol Stack includes all servo algorithms, regulators, filters, PTP-Clock based on hardware timer and direct Timer access.
The RTS IEEE 1588 stack is fully tested and comes complete with documentation and an example implementation on VxWorks for x86. The RTS IEEE 1588 Software Protocol Stack is available in source code.
About the IEEE 1588 PTP Protocol
Packet based networks like Ethernet are inherently non-deterministic. In order to gain determinism, distributed real-time applications need to be decoupled by a deterministic abstraction layer. If all nodes are equipped with highly synchronized real-time clocks, determinism can be achieved.
Synchronized real-time clocks can be essential e.g. for applications in the world of
- Test and Measurement to provide synchronized time-stamps
- Industrial Automation to allow synchronized controls
- Simulation for real-time functionality
The IEEE 1588 has found broad acceptance and for Test and Measurement or Instrumentation, it has been specified for the new LXI Protocol (LAN-based GPIB successor).
The objectives of the IEEE 1588 Standard are
- Highly synchronized real-time clocks in components of a networked distributed measurement and control system
- Intended for relatively localized systems typical of industrial automation and test and measurement environments.
- Applicable to local area networks supporting multicast communications (including but not limited to Ethernet)
- Simple, administration free installation with support of hot-plugging
- Supports heterogeneous systems of clocks with varying precision, resolution and stability
- Minimal resource requirements on networks and host components.
IEEE 1588 therefore specifies
- a method to automatically segmenting a PTP network
- the characterization of PTP clocks
- the definition and control of the Master-Clock
- the synchronization of networked PTP Clocks
- the PTP Network Management Protocol
FunctionalityThe time base in a 1588 system is the time base of the Grand Master Clock. All other clocks synchronize (perhaps via boundary clocks) to this Grand Master Clock.
When powering up an IEEE 1588 network or when nodes are joining the network, the Grand Master Clock is determined automatically and via synchronization message passing all the real-time clocks start synchronization.
Synchronization messages are passed every two seconds to keep network resource usage at a minimum.
-
IEEE 1588 Functionality - click to enlarge In the so called Sync-Message, the master sends its current time to the slave where a time stamp is generated exactly when the message is received.
- The master then sends a follow-up message to the slave with the exact time when the original sync-message had been sent. The slave then corrects its local real-time clock to the clock of the master.
- In order to eliminate the real-time clock delay of the slave due to the time it took the packet to travel over the network, the slave sends a so called Delay-request message to the master and notes the exact sending time.
- The master then replies with the time-stamp when the Delay-request message was received. The slave can then compute the exact time of the master clock and finalize the synchronization.
- Further statistical methods are used to constantly adjust the real-time clock to correct for any residual fluctuations from the physical layer, network, repeaters and switches.
More information about the IEEE 1588 Standard can be found at the following URL:
http://ieee1588.nist.gov
|
|
IEEE 1588 Tools
