Investigating USB-C Problems on Some Dell XPS and Precision Laptops

Summary: Based on information gathered while helping Plugable customers along with feedback from Dell owners on public forums, it appears some percentage of Dell USB-C systems are exhibiting unstable USB data I/O over their USB-C port.

Update 7/14/2016 – We have had several confirmed cases where lowering the Power Output of the internal Wi-Fi adapter to 75% in Dell XPS models has helped with USB-C disconnect behavior. This has also been discussed in the Dell support forum -> http://en.community.dell.com/support-forums/laptop/f/3518/t/19983555

Please see our detailed instructions for lowering the Power Output and the bottom of this post here

Update 7/11/2016 – Our initial reports from customers indicate that even with the release of the latest updates from Dell applied there are still some cases where USB-C devices may not work as expected. Several customers have confirmed that enabling ‘Airplane Mode’ is an effective workaround

Update 7/7/2016 – Over the past few days Dell has released several updates for many of their Thunderbolt 3/USB-C systems, including the XPS 13 9350, XPS 15 9550, and Precision 5510. These include updates to the system BIOS, the Thunderbolt 3 driver as well as the Thunderbolt 3 NVM firmware. Please be sure to visit http://www.dell.com/support and use your Dell Service Tag (http://www.dell.com/support/contents/us/en/19/article/Product-Support/Self-support-Knowledgebase/locate-service-tag/Notebook) to locate, download and install the latest updates for your system as a first troubleshooting step should you encounter any issues with our USB-C docking stations with a Dell system.

The BIOS updates will be under the ‘BIOS’ category, while the Thunderbolt 3 driver and NVM firmware updates will be located under the ‘Chipset’ category. Best practice is to update the BIOS first, the Thunderbolt driver second, and NVM firmware third.

Plugable recently launched two USB-C docking stations (https://plugable.com/products/ud-ca1 and https://plugable.com/products/ud-ultcdl) and they have proven to be very popular; so much so that we’re having trouble staying in stock. Any time we launch a new product, especially one (or in this case two) that makes use of a new technology such as USB 3.1, support engineers like myself always learn a lot in the first few weeks. (For a quick synopsis of our data points, jump to the end of post.)

Plugable UD-ULTCDL Ports

Plugable UD-ULTCDL USB-C Triple Display Docking Station

The vast majority of customers reported both units worked well with many popular models of USB-C systems (we have compatibility tables on the respective product pages), which aligned with the results we observed while developing the devices. But there were of course cases where things did not. At Plugable those who help develop a product also provide the support, and in the normal course of troubleshooting certain patterns often emerge which we view as an opportunity for further investigation into various issues that might occur.

What’s been most interesting with our USB-C docks was that when things didn’t work as expected, they would do so in an extremely inconsistent manner, often manifesting with instability of attached USB devices. For example, a customer with a Dell Precision 5510 laptop was experiencing random disconnects when using one of our docks. After investigating the behavior via our handy diagnostic tool PlugDebug (https://plugable.com/support/plugdebug) we elected to send a pretested replacement dock to rule out a hardware problem. Plugable is different from a lot of other companies in that when we send replacements they are tested at length by a human being in our lab. Despite this effort, when the customer received the replacement (which had been tested over 12 hours) the behavior was still present.

Our support engineers set out to better understand the issue. Why did the docks work great for the vast majority of customers’ XPS 9350 and 9550 systems (and Plugable’s identical in-house test systems) while a handful of other customers with the same systems were having problems, even with a known good tested replacement docking station?

We collectively scratched our heads and dug deeper. Our first focal point was nearly all of these problem reports were coming from owners of Dell Thunderbolt 3-enabled systems like the XPS 13, XPS 15 and Precision 5510. (The same chip which enables Thunderbolt 3 functionality on these systems also enables USB 3.1, which is the protocol used to communicate with our USB-C docks.)

Since Dell’s XPS lineup are among the most popular Thunderbolt 3/USB-C systems it was no surprise to see them well represented with our customers, but what was so surprising was this small percentage of systems which we knew to be compatible yet were not working as expected.

Having just launched our first Thunderbolt 3 products (https://plugable.com/2016/05/25/thunderbolt-3-dual-4k-display-adapters-shipping), we knew very well that all Thunderbolt 3 systems were receiving frequent BIOS and Thunderbolt 3 firmware updates which dramatically help Thunderbolt 3 and USB-C stability. Yet even with these updates applied on certain systems we still saw issues in specific instances.

TBT3-DP2X Adapter

Plugable Thunderbolt 3 Dual DisplayPort Adapter

Digging deeper, we found references to similar behavior online within Dell’s support forums (http://en.community.dell.com/support-forums/laptop/f/3518/t/19677047?pi41097=1) for some users of Dell’s Thunderbolt 3 and USB-C docking stations. While the thread is quite long, it does reflect similar unstable dock behavior while also indicating the common theme of the whole USB bus resetting or disconnecting and causing problems.

As official Dell comments on the thread have dropped off, customers have tried their own pragmatic approach in finding work-arounds and some (but not all) have found the behavior diminished if the laptop was run with the lid open. Others found that putting the system in ‘Airplane Mode’ to disable the internal Wi-Fi and Bluetooth adapter helped. And there’s even multiple users who report working with Dell engineering on the issue, stating that Dell is aware of the problem on some systems and working on a fix in the form of a BIOS update.

Note that Dell recently posted a BIOS update for the Dell XPS 13 9350 and the Release Notes indicated Thunderbolt 3, USB-C and Docking station fixes. Unfortunately this update was removed by Dell shortly after it was posted (https://www.reddit.com/r/Dell/comments/4opu4b/xps_13_9350_bios_143_has_been_pulled/)

Even with our growing suspicions that some host systems were a key part of the problem, we didn’t feel certain about this until we worked through an especially tricky support case involving an XPS 15 9550 and our Triple Display Dock. In the course of troubleshooting USB disconnection issues mentioned above we again sent a pretested replacement dock to rule out a hardware problem but again the issue remained. The customer even went to the extraordinary length to have Dell replace the system, and yet the issue remained. In this case we actually sent the customer some additional Plugable USB 3.0 products an effort to isolate the behavior further. Using our UD-3900 dock with an adapter via the Dell’s USB Type-C port produced the same disconnect symptoms, but when used via the Dell’s USB Type A port it worked as expected. As our investigation continued the customer replaced his system a third time for a reason unrelated to the dock behavior, and lo and behold both our UD-3900 and our USB-C Triple Display Dock were now working properly via the Dell’s USB-C port.

So where does this leave us? While we have many test systems in our lab, we do not have an example of every model Dell system that has Thunderbolt 3 and USB-C. In our internal testing with the Dell XPS 13 9350 and Dell XPS 9550 (non-hybrid) both of our USB-C docks work well. We are hopeful based on Dell forum comments that updated system BIOS files or Thunderbolt 3 NVM firmware will be released to help with the behavior. Though we don’t know if in some cases the solution will go beyond BIOS/firmware updates and instead is indicative of a hardware problem with the host system itself.

Interestingly as we were putting the finishing touches on this post before publishing, Dell has posted a BIOS update for their Thunderbolt 3/USB-C Precision 7510 and 7710 models http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=7HGW6 that indicate various Thunderbolt 3 and USB-C fixes. Our hope is that these changes will filter down through their other models in the near future.

In the meantime, if anyone encounters issues with our USB-C products and a Dell USB-C or Thunderbolt 3 system please contact us directly at support@plugable.com and we will be happy to help. We thank all of our current and future customers for their patience and feedback as we continue to learn about the various USB-C systems and how our products interact with them.

Synopsis
Here are the data points we’ve gathered from customer tickets and the other public resources mentioned in this article:

  • The behavior seems to only affect a small number of systems (relatively speaking, given the popularity of Dell’s systems)
  • We have seen similar reports from owners of: Dell XPS 15 9350, Dell XPS 15 9550, and Dell Precision 5510
  • The instability primarily affects transmission of USB data packets; Alternate Mode video seems much less likely to be impacted
  • Turning on Airplane Mode can help minimize issues
  • Using the system with the lid open can help minimize issues
  • Some users report better behavior when maximizing the distance of the USB-C peripheral from the system (i.e; use all available cable length)
  • Per multiple user confirmation on the Dell thread above, Dell will be implementing a BIOS fix “soon”
  • Dell has already released, then pulled, a BIOS update for the XPS 13 9350 which indicated it contained several fixes related to USB-C and Thunderbolt 3 stability
  • Some users who installed the update before it was pulled by Dell report diminished WiFi signal strength after applying the update
  • On the Dell forums, one user reported calling Dell to troubleshoot his USB-C issues and was sent a replacement laptop that fixed the issues
  • Plugable has worked with a customer who was experiencing USB-C device instability using his XPS 15 connected to our Triple Display Dock. After replacing his docking station with a pre-tested known good unit and still having problems, the customer replaced his XPS twice(!). The second replacement XPS he received solved the issue
  • Given the impact of the factors above (Airplane Mode, distance from the PC, the BIOS update impacting WiFi, etc) it seems very possible the wireless/Bluetooth module in some systems might generating interference with the integrity of USB-C data. (Yet another reminder of the complexities of high frequency signaling!)

Instructions for lowering Power Output of the internal Wi-Fi adapter in Dell XPS

1. Open Device Manager
2. Expand the ‘Network Adapters’ category
3. Right-click on the entry for the Wi-Fi adapter and select ‘Properties’
4. From the ‘Advanced’ tab, scroll down and select ‘Power Output’ from the ‘Property’ column, and then select 75% in the ‘Value’ drop down (example screenshot below).
5. Click OK to commit the change.
6. Reboot the system

XPS 13 9350 WiFi Power Setting2

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