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Embedded DisplayPort (eDP) is finding success in applications such as automotive displays, laptop and tablet displays, and even smart phones. One key feature of eDP is Advanced Link Power Management (ALPM). As you can tell from the name, this is an “advanced” feature of the protocol, and it often causes headaches for design engineers and validation engineers alike. At Introspect Technology, we’ve developed sophisticated tools to help deal with the complexities of testing and verifying ALPM mode in your latest eDP design!

What is ALPM Anyway?

ALPM is a feature that enables fast wake and fast sleep capability in a sink device. To save power, the sink is required to go to sleep as quickly as possible (based on a command from the source). More importantly, it is expected to wake up rapidly once active video is transmitted again from the source. Active video can be either a regular stream, a compressed stream, or even a panel self refresh (PSR) stream.

If the above sounds familiar, it’s because other display standards like those based on the MIPI D-PHY and C-PHY physical layers have enabled such rapid sleep and wake capability for more than a decade now. As a pioneer in MIPI testing, Introspect has developed a wealth of experience in making solutions for testing the very rapid transitions between sleep and wake states in MIPI video technologies, and we’re happy to bring this experience to eDP.

The Three Test Scenarios

There are three situations covered in this blog. If you’re developing a display driver IC (DDIC), a panel, or a timing controller, then you need a solution for testing a sink device. This is the first scenario described below. On the other hand, if you’re developing a GPU or microcontroller, then you need a solution for testing a source device, and this is the second scenario described below. Finally, if you’re an original equipment manufacturer (OEM) putting together the next innovative system or IoT device containing both an eDP link, then you need to test both the source and the sink interoperating together. This is the third situation covered in this blog.

Testing a Sink Device

Figure 1 shows how an Introspect SV5C-eDP Embedded DisplayPort Generator can connect to an embedded display panel directly.

Figure 1: Connecting the SV5C-eDP Generator directly to an embedded display panel.

 

With this connection, you have access to all the signals needed to train the eDP link and light up the panel. This happens through Pinetree, which has a wealth of tools for verifying eDP receivers. For example, the following figure shows a stream component where we set the “Transmission Mode” to be an ALPM transmission.

Figure 2: Setting the Transmission Mode to be an ALPM transmission.

 

Testing a Source Device

Just like when testing sink devices, you can use an Introspect SV5C-eDP Embedded DisplayPort Analyzer to test source devices directly, without requiring any other equipment. Specifically, this analyzer can terminate a source device and act as a sink. Simply choose the capability that you want to verify (e.g. maximum data rate) and then let the analyzer train itself with the source under test.

What’s more, during the training process with the source device under test, the analyzer – naturally – keeps a data record of all transactions on the main link and the AUX channel, and it gives you a detailed, time-correlated view of everything that happened during training. Figure 3 shows an example of how the analyzer captures the very first power up sequence of a source device.

Figure 3: Capturing the first power up sequence of a source device.

 

Testing a Live System Containing Both a Source and a Sink Device

This is the scenario that is most interesting for us here at Introspect because it is often the most challenging. The challenge with it has to do with probing, and this is where the Introspect Remote Sampling Heads shine. This technology provides high-impedance, low-loading, and very high bandwidth active probe technology to the consumer electronics market. It allows for sniffing any eDP application, an example of which is shown in Figure 4.

 

Figure 4: A Remote Sampling Head with the SV5C-eDP Analyzer as part of a neat sniffing setup for an eDP application.

 

As can be seen, the solution for live system testing now consists of the analyzer and the Remote Sampling Head. It is very clean!

Below is a trace for catching the ALPM mode in action. As can be seen, the analyzer is able to react almost instantaneously and provide incredible visibility in the process of fast training that happens in ALPM mode.

Figure 5: The Pinetree software provides immediate insights into the data that is collected in ALPM mode.

 

Summary

As an advanced feature of Embedded DisplayPort, Advanced Link Power Management can create challenges for engineers working on new eDP applications. We’re thrilled to help simplify the verification process so that you can focus on your design tasks at hand. Whether you are testing a source device, a sink device, or a complete embedded system containing sources and sinks, Introspect offers a complete portfolio of DisplayPort products. Our solutions also cover regular DisplayPort (v2.1) and even custom implementations that are sometimes needed in order to enhance competitiveness and differentiation by our customers in the marketplace.

What’s your latest DisplayPort or Embedded DisplayPort challenge? Get in touch with the Introspect team, and let us find the best approach and solutions to your design obstacles. Send us an email at info@introspect.ca today.

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