Capabilities of PXIe-8521: Not just a workaround!

15. September 2020

Every single NI Silver System Integrator use wide range PXI cards on daily basis, and in Kentigen, we are not an exception. In the following lines, we share one of the key advantages of the automotive ethernet card PXIe-8521 towards BroadR — Reach – Ethernet media converter. Furthermore, we present NI example for BroadR-Reach card for our solution.

The main difference between BroadR-Reach (BR) and the common 100-BASE-TX Ethernet is the physical layer. BR allows full-duplex communication through a twisted pair of wires. This gives its usage for cost-effective applications in automotive, preferably used for ADAS systems. The BroadR-Reach has been standardized as 100BASE-T1, so the terms “100BASE-T1”, automotive Ethernet and BroadR-Reach usually mean the same thing.

Topic scenario

Our customer focused on ADAS systems needed to implement Video injection in HIL. For such an application, time synchronization is crucial factor to have reliable results.

Challenge

In the injected frames a timestamp drift occurred. This drift was caused by using 2 different time-sources:

  • Video and CAN timestamps – time-source from used PXI chassis of the replay system
  • BroadR-Reach timestamps – timebase of the generic driver of the embedded controller’s ethernet interface

As the BR stream depends on the contents of the video stream, their relative sync can be measured. Because of different time-sources, significant time drift appeared after few hundreds of frames. This desynchronization needed to be compensated by sending Video frames earlier (see in the picture).

Solution

The automotive ethernet card PXIe-8521 from NI is able to use the same PXI chassis clock source as the other NI hardware used. The timestamps are therefore inherently coherent. Moreover, the PXIe-8521 is able to use the shared trigger lines of the chassis to synchronize the start trigger time of all the streams used.

NI Example demonstration: Ethernet AVTP Compressed Video Format

We created a loopback on PXIe-8521 card in our lab PXI chassis. Firstly, interface should be configured in NI MAX. ENET2 has been configured as Master and ENET4 as Slave.

Demonstration project should be found in C:\Program Files\National Instruments\LabVIEW 2017\examples\nixnet\projects\NI-XNET Ethernet\Ethernet AVTP Compressed Video Format.lvproj. It consists of receiving VI and transmitting VI, that is streaming sample video using Audio-Video Transport Protocol (AVTP). Sending VI (a.k.a. output stream) uses ENET2 / master interface. It also shows Sent packets and video frames.

Receiving VI (a.k.a. input stream) then uses ENET4 / slave interface. There is a possibility to skip some video frames by putting them into buffer (150 in picture below) or we can use 0 to see the whole original stream. On the right there are some further parameters. If Stream ID matches, their values should match their counterparts in Output Stream VI. Noticeable parameter is Resolution that is calculated from array of packets that corresponds to a single frame.

We have just started…

Needless to mention that although those are main VIs of the example project, there are also some interesting VIs inside other example projects, e.g. Ethernet Basic Input and Output (Ethernet Writer and Ethernet Reader that can be also tried with Output Stream VI to see raw data. Another project, definitely worth to try, is Ethernet Time Sync Protocol. This can be run on master interface and slave interface as 2 different instances to see synchronized state and synchronization details (parameter differences).

By slow steps to bare-metal

Not only for debugging off-site but also for playing around with new technologies, we use rack-mount PXI-based system and other supported hardware. On this system we created loopback on PXIe-8521 and so it was able to gave born to this, PXIe-8521 example demonstration.

What else?

Summary? – Yes! Demonstration capabilities of PXIe-8521 BroadR-Reach card for PXI chassis are unfathomable, especially in automotive computations like Autonomous Driving Assistance Systems (ADAS). We have not only presented how to transport small video shot via local loopback, but how it can resolve critical engineering issue right-away.