Dell USB-C Discussion

Discussion in 'Dell XPS and Studio XPS' started by MLev1777, May 2, 2016.

  1. MLev1777

    MLev1777 Notebook Consultant

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    I created this new thread as a Dell USB-C specific discussion place as the XPS threads are getting fairly large and many of these questions that are currently dispersed between different threads affect multiple models. If that's not reasonable, please feel free to delete.

    My questions is, does anyone know if the Dell USB-C to HDMI/USB 3.0/VGA/Ethernet uses the DisplayPort Alternate Mode to create the HDMI and/or VGA video signals? Or does it create a video signal by conversion from a USB data line as the older, USB-3.0, hubs do? I'm asking because this significantly changes the value proposition of the adapter (affecting both CPU usage and power draw), and for the first time the other day I noticed the adapter was extremely hot, possibly suggesting it is performing some significant processing functions and is not using native Display mode signals. Thought someone may know how to check this using Windows or Intel Control panels.
    Did a Google search, some links are below, but was unable to find a definitive answer.
    http://en.community.dell.com/techcenter/os-applications/f/4613/t/19681911
    https://www.reddit.com/r/Dell/comments/3w3hsa/usbc_hub_for_the_xps_13/
     
  2. Eason

    Eason Notebook Deity

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    Pretty sure it's alternate mode, because it's not a dock with hardware inside it like the older display/audio docks. I've never noticed it being anything other than warm. Were you powering a lot of USB devices through it?
     
  3. MLev1777

    MLev1777 Notebook Consultant

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    No, just using 1080p ext monitor via HDMI and had a wireless mouse/keyboard transceiver in the USB. I also assume it doesn't always heat up like you said, as this is the first time I noticed it.
    I ask because the very similar USB-A (3.0 speed) adapter uses a USB conversion to video/HDMI out and thus increases CPU usage. If this one just uses the displayport alternate mode data stream, then it doesn't really require much processing. I'm a bit concerned that Dell cut some cost/corners and just replaced the USB-A plug on the model below with a USB-C for new one, which is definitely not what I expected when ordering.
    http://accessories.dell.com/sna/productdetail.aspx?c=us&cs=19&l=en&sku=470-ABHH

    For Everyone: I figured this thread would be a good place to post all USB-C questions for the Dell XPS models to make an easy resource for people to browse instead of individual threads. Please feel free to post other questions/topics
     
  4. Eason

    Eason Notebook Deity

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    lol I don't think that's possible. The TB3 port is functionally very different than USB A.
     
  5. MLev1777

    MLev1777 Notebook Consultant

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    Yeah, I agree with your thought that it probably uses the native displayport channel rather than USB conversion, but I think you'd be surprised at how functionally similar the TB3 is (more specifically: can be) to USB-A. I am by no means an expert, but here's my understanding based upon some research I did before buying the XPS 15.

    For clarity, USB-C and USB-A refer to the port and cable type and not directly to the data transmission specification. That's more USB 2.0, 3.0, and 3.1, which although require certain port features, refer to data transmission (and mostly the rate). Most USB-C ports support USB 3.1, but I know of devices that are only 3.0 and I think some are USB 2.0 transmission.

    The full USB-C specification additionally allows the port to assume alternate modes, in which a different data transmission model can access/control some or all of the USB data lines in the 24-pin connector. TB3 is one of these alternate modes and, with the Alpine Ridge Controller that drives it, actually allows for the TB3 port (that is mechanistically a USB-C port) to act as a regular USB (USB 3.1 but is backwards compatible), DisplayPort, Thunderbolt 3, or PCIe connection. These different data transmission types can also exist in combinations, and the type is set after communication between the host and device. For instance, you can attach a completely passive adapter to convert the TB3 port to a USB-A port and it will just function using just the regular USB 3.1 data transmission specification.

    Back to the point: since the TB3 port on the Dell XPS can function as any one of these, I was concerned the it was functioning as a USB only device as opposed to using both USB and DisplayPort alternate mode. [On a side note: I highly, highly doubt the dongle uses any true Thunderbolt 3 technology, as not only would it be overkill but the product page doesn't specify that it requires Thunderbolt 3 (as the TB15 dock does) but just USB-C (similar to the WD15 dock)]. This is an over-simplification, but essentially the downside to it only using USB data transmission would be that the output video stream has to be encoded by the iGPU, then sent to the CPU for encoding into USB data, then to the Alpine Ridge to the TB3 port to the dongle where it would then have to be decoded (or really converted) into the HDMI specified data stream. Essentially it would function as if you bought the USB-A dongle version I mentioned above and plugged it into a USB-C to USB-A adapter and that into the TB3 port. It would work, and probably save Dell some development costs. However, if it uses the DisplayPort streams to drive the HDMI, it basically functions as an on-board port would, and the DisplayPort video data can be transmitted directly from the iGPU to the dongle. It has to be converted at that point to an HDMI compatible signal, but this requires much less processing and therefore leads to decreased CPU utilization, lower power consumption by the dongle, and a better quality display output (less lag mostly).

    Again, I think you're right that it probably has been redesigned to utilize the newer features of the USB-C port and the displayport alternate mode. There's virtually no lag on the monitor for me, and I only once noticed it heating significantly. Guess I'm just becoming rather skeptical of Dell with new tech, and was hoping someone could prove it.

    Here's a few articles about what I mentioned earlier if anyone wants to read them.
    http://www.displayport.org/pr/vesa-brings-displayport-new-usb-type-c-connector/
    http://www.cnet.com/news/thunderbolt-3-and-usb-type-c-join-forces-for-one-port-to-rule-them-all/
    And here's the link to the full USB-C specs, which I admittedly only glanced through for the info I wanted as it is fairly dense
    http://www.usb.org/developers/docs/
     
    Last edited: May 3, 2016
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  6. Eason

    Eason Notebook Deity

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    Good info, but as there's no lag and I keep a close eye on my CPU usage (C7% 95% and above) I'm nearly positive it's using proper channels.
     
  7. link626

    link626 Asus GL502VM, Lenovo Y580, Asus K53TA

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    dunno if i'm adding to the discussion, but I bought the dell usb-c to hdmi 2.0 adapter, and it also ran warm
     
  8. MLev1777

    MLev1777 Notebook Consultant

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    Thanks. Pretty sure that backs up the thinking of Eason and I above as warm is much different than hot.
    I looked at the other USB-C thread you just posted one, and the part mentioned where plugging in a USB-C to DisplayPort cable does not cause any notifications or changes in device manager, is exactly the behavior I'd want to see from a cable properly utilizing DisiplayPort Alternate mode. In that case, its not a device or peripheral but just a simple cable, which is very cool. For the adapter obviously some new devices must pop-up in device manager (Billboard device) as it has 4 functions, so dont think it indicates much.
    One a side note, does your Dell USB-C to HDMI 2.0 adapter function correctly as a HDMI 2.0 port, as in supplying a 4k 60Hz signal?
    Also, saw you asked the person to connect 3 monitors at once to test for flickering. Why? Are you having a specific issue?
     
    Last edited: May 4, 2016
  9. Bommel87

    Bommel87 Notebook Consultant

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    The Dell adapters are only specified up to 1080p (both the USB 3.0 and USB-C). 4k does not work.

    [Edit]:
    This is the reason I bought the USB 3.0 adapter (as the USB-C one was out of stock everywhere). At that time, I did not reckon about the exact transfer mode and corresponding CPU usage.
     
  10. link626

    link626 Asus GL502VM, Lenovo Y580, Asus K53TA

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    yes, I can get 4k @ 60 4:4:4: from the Dell usbc hdmi 2.0 adapter. Tried it on 2 different 4k monitors and 4k TV.

    Flickering issue = if I plug in the usb-c adapter first, then the built-in hdmi port, triple monitor does not engage stably, and starts to flicker like it's struggling to figure out the connections.

    If i plug in the hdmi port first, then the usb-c adapter second, then triple display is stable, no flicker.
    The order I plug it in makes a difference.

    However, I should mention that I do not have an xps 9550. I have an asus with the same kind of ports, and want to see if xps9550 owners are having the same problem
     
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