Prerequisites, Limitations, and Unsupported Features

The Simulink® Real-Time™ implementation of PTP enforces specific requirements and limitations.

Prerequisites

  • PTP functionality is available only with a Speedgoat target computer. If you have not installed the Speedgoat library, attempting to build a real-time application with PTP causes a build error.

  • IEEE 1588 protocol support includes:

    • PTP over UDP is supported on Intel® 82574 Ethernet cards and Intel i210 Ethernet cards.

    • PTP over Ethernet is supported on Intel 82574 Ethernet cards.

    To check that you have the required card, start your target computer. In the Command Window, type:

    tg = slrt;
    getPCIInfo(tg, 'Ethernet')

    Check that you see an entry like this entry:

    Intel                    82574L
         Bus 5, Slot 0, IRQ 10
         Ethernet controller
         VendorID 0x8086, DeviceID 0x10d3, SubVendorID 0x15bd, 
               SubDeviceID 0x100a
         Released in: R2010a
         Notes: Intel 8254x Gigabit Ethernet series

Limitations

  • The PTP network card clock acts as PTP clock. Only one clock is allowed per node.

  • Run the model in Real-Time execution mode, not in Freerun mode or driven by an external interrupt. In the latter two cases, the PTP message transmission intervals can violate the PTP standard.

  • You can include only one PTP configuration block in a model. You can run only one real-time application on a target computer. If you have installed multiple PTP Ethernet cards on your target computer, you can use only one of them for PTP at a time. You can use the other PTP Ethernet cards for non-PTP purposes.

  • The PTP message transmission intervals (Announce interval, Sync interval, and Min delay or pdelay request interval) must be greater than the block sample time. Too small a message transmission interval causes a model update error.

  • Simulink Real-Time can transmit PTP messages only at a multiple of the block sample time. If a transmission interval is not a multiple of the block sample time, PTP transmits the messages at the nearest multiple to the specified transmission time. As a best practice, specify all transmission intervals as integral multiples of the block sample time.

  • The specification requires that a PTP node issue messages within ±30% of the message transmission intervals at least 90% of the time. To meet this requirement, specify message transmission intervals (Announce interval, Sync interval, and Min delay or pdelay request interval) at least three times the base sample time.

  • The following factors limit accuracy:

    • Network protocol stack delay fluctuation

    • Network technology component delay fluctuations (switches, routers)

    • Clock timestamp accuracy

    • Clock oscillator stability

    Use components that minimize these factors. For example, you can use a transparent or boundary PTP clock to increase synchronization accuracy.

    • A transparent PTP clock tracks the amount of time a PTP message takes to go through the device. It passes that information to nodes receiving the message.

    • A boundary PTP clock has multiple PTP ports that can act as a master clock or a slave clock.

  • Some systems require a PTP time source that is traceable to an International Atomic Time (TAI) clock, such as a GPS signal. To support traceability, acquire a third-party grandmaster PTP clock that provides this capability. In that case, a Simulink Real-Time target computer running PTP acts only as a slave clock.

Unsupported Features

  • Simulink Real-Time supports only PTP version 2, as defined in IEEE® Std 1588-2008. If a Simulink Real-Time PTP node receives a PTP version 1 message as defined in IEEE Std 1588-2002, it ignores it.

  • The Simulink Real-Time implementation of PTP does not support the following functionality defined in IEEE Std 1588-2008:

    • PTP variance computation, as described in IEEE Std 1588-2008 Clause 7.6.3.

    • PTP nodes configured as one-step PTP clocks, as described in IEEE Std 1588-2008 Clause 3.1.21.

      You can configure the master node as a two-step clock only, as described in IEEE Std 1588-2008 Clause 3.1.47.

    • PTP management messages, as described in IEEE Std 1588-2008 Clause 15.

      A Simulink Real-Time PTP node cannot transmit a PTP management message. When a Simulink Real-Time PTP node receives a PTP management message, it ignores it.

    • PTP signaling messages, as described in IEEE Std 1588-2008 Clause 13.12.

      A Simulink Real-Time PTP node cannot transmit a PTP signaling message. When a Simulink Real-Time PTP node receives a PTP signaling message, it ignores it.

    • Optional features, as described in IEEE Std 1588-2008 Clause 16 and Clause 17.

Related Topics