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openPOWERLINK
An open-source POWERLINK protocol stack

Frequently Asked Questions (FAQ)

Check out the FAQs before putting any questions to the discussion forum.

Technology

Q: What is POWERLINK?
A: Ethernet was originally designed for office applications and is not deterministic (due to CSMA/CD, latency and queuing in switches...). To fulfil requirements of industrial automation and process control the concept of real-time industrial Ethernet was introduced to the market. POWERLINK is the most known of these real-time industrial Ethernet solutions. POWERLINK is a software protocol based on standard Ethernet. Deterministic fast reaction time is ensured via through a mix of timeslot and polling procedures.

Q: Why should I use POWERLINK?
A: If your application requires deterministic fast reaction time, POWERLINK is the right solution. POWERLINK is based on standard Ethernet and does not require any specific proprietary hardware (ASIC...). POWERLINK brings your application unmatched performance at the lowest cost.

Q: In which applications can I use POWERLINK?
A: POWERLINK is running various applications in all industries, e.g. audio/video, automotive, distributed control systems, energy management, machinery, industrial automation, railway and maritime transportation, robotics, uninterruptible power supply, vision systems...

Q: Where can I get more information about POWERLINK in general?
A: Please checkout the website of the Ethernet POWERLINK Standardization Group (EPSG) at http://www.ethernet-powerlink.org/

Diagnostics

Q: How can I diagnose a POWERLINK network?
A: PLCs running as a POWERLINK master often have a logging mechanism through which errors are reported. Check the logger for any entries that refer to POWERLINK.
POWERLINK itself also keeps error counters on each device. The counters include loss of frame errors, CRC errors, timeouts... and can be read via SDO from the according objects.
Additionally, any standard network tracing tool can be used to diagnose at network level. The two most commonly known ones are Wireshark (Open Source) and OmniPeak (commercial). You just need to connect your PC to the network and run the tool in order to see the traffic for diagnosis. You should connect the PC via a hub to the POWERLINK network, and all protocols (TCP/IP...) shall be deactivated on the tracing interface. For high-precision network traces, the use of an Ethernet analyzer hardware is recommended.

Q: How can I calculate the POWERLINK cycle time?
A: The minimum possible POWERLINK cycle time is determined by the number of nodes on the network and the amount of data transmitted to and from each node.
Each network, has the following frames:
   1x SoC (64 Bytes)
   nx PReq/PRes (64-1518 Bytes)
   1x SoA (64 Bytes)
   1x ASnd (318-1518 Bytes)
The time of transmission is calculated by the total amount of bits on the network (Ethernet frame size in Bytes * 8 + 64 bit preamble). Of this, the bittime on the network is determined (Bits on the network * 10ns). The reaction times have to be added (ideally, 960ns inter frame gap between all frames).

Q: I have done a network trace in which I see non-POWERLINK frames. What is wrong?
A: On a standard PC, network interfaces are usually configured for TCP/IP networks and try to establish communication channels to other PCs or the Internet (e.g. DHCP to request an IP address, SMB traffic to find Windows shares, HTTP...). This traffic is visible in the network trace and might also influence your POWERLINK network.
Therefore, all protocols shall be deactivated on the interface you are using for the network tracing. The steps on how to do this are different on different operating systems. In Windows you can deactivate all protocols in the adapter settings of the network card.

Q: In my network trace, I see some frames coming in the wrong sequence, but no error is detected by the master. What is wrong?
A: It is very likely that there are problems with the network trace. In order to get a good trace, you should use a separate PC connected via a hub to the other devices and deactivate all protocols on the tracing interface. For deterministic tracing with precise time stamping, the use of a network analyzer is recommended.

Q: In my network trace, I see some frames coming in the wrong sequence and the Master cyclically sending a reset command. What is wrong?
A: The PollResponse Timeout value is set too low. You need to increase this value (CN parameter in the network configuration tool) in order to have the MN waiting longer for a response. This can happen if a device is placed behind several hubs or long cables due to the propagation delay.

Q: How do I find sporadic errors in a POWERLINK network?
A: As a first step, you should isolate the problem and make it reproducible. Use of filtering function of network traces will help localize and identify the error. With some network tools it is possible to enable triggering functions, which help trace collection when the sporadic error appears.

Q: I am using an openPOWERLINK MN and have some problems with my slave devices. Whom can I contact?
A: Your first contact will be the support team of your device manufacturer. In order to efficiently get help, prepare information such as the device type of the slave, the according xdd file, the platform of your openPOWERLINK MN (CPU type, operating system, stack version), any error logs from the device or the master and - if possible - a Wireshark trace visualizing the problem.

Q: What is the available asynchronous bandwidth?
A: The amount of data transmitted in one asynchronous frame is determined by the Asynchronous MTU (Maximum Transfer Unit). This value can be set in the network configuration tool on the master side. By changing the value, more asynchronous bandwidth is allocated, and therefore higher throughput is achieved.

Q: What is the difference between static and dynamic mapping?
A: The PDO mapping determines what data is cyclically transmitted to and from the network. If a device uses static mapping, the mapping configuration is fixed by the device manufacturer and cannot be changed by the user. If a device uses dynamic mapping, the configuration can be set by the user according to the application's requirements.
Typically, devices with few cyclic data like encoders or sensors use static mapping, while devices with lots of settings like drives use dynamic mapping.

Q: My network configuration tool (openCONFIGURATOR) does not accept my device description file (xdd). What can I do?
A: You can validate your xdd file using the online xdd checker on the EPSG website. If the checker reports errors, get in contact with the device manufacturer providing the xdd file. If the checker does not report any error, report the issue in the openCONFIGURATOR forum.


General

Q: I have a question that is not answered here. What to do?
A: Please use the openPOWERLINK forum on SourceForge for further discussions.