4 ms·

and USB-C allows the transmission of displayport over USB-C

by FinnKuhn 3y ago

jsheard 3y ago
It also allows the transmission of HDMI over USB-C, so you still have two competing standards
- hadrien01 3y ago
  There's also Thunderbolt over USB-C that does DisplayPort, but it doesn't support all the same versions as DisplayPort over USB-C. And there's also USB 4 but I don't know/understand if it changes anything.
  - masklinn 3y ago
    I think the most applicable bit is that USB4 adds tunneling modes, aside from alternate mode. I'm not entirely clear, but from my understanding alternate mode means the physical connection gets switched over, while tunneling means the tunneled data is sent over USB (so the communication on the wire is USB all along, you get nesting).
    - jsmith45 3y ago
      This is essentially correct, although the encapsulation format is really the Thunderbolt encapsulation format, which is only USB in that it is now officially defined in the USB4 specification. USB4 hubs/docks for example, need to have the ability to translate from encapsulated DisplayPort to alternate mode for its downstream ports. USB4 hosts need to support both encapsulated and alternate modes in the downstream ports. The idea is that if a display device does not want to implement any other non USB 2.0 peripherals (2.0 has dedicated lines so it can support those), it can implement only alternate mode, (and not need to support the complexities of encapsulating USB4), plus all USB4 hosts needing to support DisplayPort means you know you can connect such a screen to any USB4 device and have it work (although supporting multiple screens like this is optional). One thing to not though is that DisplayPort alternate mode has the option of reversing the device->host wires of USB-C lanes and thus get 4 lanes of host->device data, for 80Gbps at Gen 3 speeds if using both lanes. USB4 V1.0 does not support lane reversal, and USB4 V2.0 can reverse only one bidirectional lane, since it still needs to support device->host data. I think this lane reversal is only possible when using the new new Gen 4 speeds, which provided 80Gbps symmetric, or 120/40 Gbps asymmetric.
- vel0city 3y ago
  It allows it, but can you actually buy any products for it? https://www.notebookcheck.net/The-demise-of-HDMI-over-USB-C-Alt-Mode-and-more-power-in-cables.680552.0.html https://www.notebookcheck.net/The-demise-of-HDMI-over-USB-C-... > True USB-C to HDMI adapters are no longer going to be a thing. The HDMI Alt Mode is more or less history, and DisplayPort has won. Notebookcheck spoke to HDMI LA and the USB-IF about it. > HDMI LA said that it doesn't know of a single adapter that has ever been produced. Similarly, at the USB Implementers Forum (USB-IF), people who are familiar with the certification process have yet to see a true USB-C to HDMI adapter.
  - bandrami 3y ago
    There's an oscilloscope screen that does the conversion in software and was the bane of my existence last year.
  - ianburrell 3y ago
    There is also MHL alt mode. The HDMI alt mode was horrible because it used the whole USB-C cable as HDMI cable preventing any other users. MHL is HDMI but over a single pair. My understanding is that all the USB-C to HDMI adapters are using DisplayPort because that is more widely supported by devices. And the conversion chips are just as cheap as MHL to HDMI.
  - mr_toad 3y ago
    > have yet to see a true USB-C to HDMI adapter Not sure what this article means. I have a USB-C to HDMI adapter (made by Apple) and a USB-C to HDMI cable and both work.
    - ThatPlayer 3y ago
      The article talks about how adapters like yours use the DisplayPort Alt Mode protocol and then have a DP to HDMI adapter integrated. Rather than implementing the HDMI Alt Mode protocol which also works over USB-C.
- jdiff 3y ago
  The article mentions the death of HDMI altmode. Is it actually widely supported?
  - jsheard 3y ago
    It seems not, I missed that HDMI altmode is still stuck at HDMI 1.4 and they're not making any attempt to bring it up to HDMI 2.0. DisplayPort indeed won in that case.
- Zekio 3y ago
  no vendors implemented it, so whenever you are currently doing hdmi over usb-c it is actually hdmi over dp over usb-c
  - johnwalkr 3y ago
    Which is fine and should stay well-supported because HDMI is also here to stay. The trend for TVs is to include HDMI ports but no displayports.
- babypuncher 3y ago
  The problem is these two competing standards solve overlapping but distinct problem sets. DisplayPort was designed to be used for computer monitors, while HDMI was designed for home theaters. This may not seem like a very meaningful distinction to most people, but it would become readily apparent to anyone trying to design a home theater around DisplayPort instead of HDMI. Off the top of my head, DisplayPort lacks any equivalents for ARC, Auto Lipsync, and CEC. Odds are your home theater makes use of at least two of these features, even if you don't realize it.
- deleted 3y ago
  [deleted]

and USB-C allows the transmission of displayport over USB-C

jsheard 3y ago

It also allows the transmission of HDMI over USB-C, so you still have two competing standards

hadrien01 3y ago
There's also Thunderbolt over USB-C that does DisplayPort, but it doesn't support all the same versions as DisplayPort over USB-C. And there's also USB 4 but I don't know/understand if it changes anything.
- masklinn 3y ago
  I think the most applicable bit is that USB4 adds tunneling modes, aside from alternate mode. I'm not entirely clear, but from my understanding alternate mode means the physical connection gets switched over, while tunneling means the tunneled data is sent over USB (so the communication on the wire is USB all along, you get nesting).
  - jsmith45 3y ago
    This is essentially correct, although the encapsulation format is really the Thunderbolt encapsulation format, which is only USB in that it is now officially defined in the USB4 specification. USB4 hubs/docks for example, need to have the ability to translate from encapsulated DisplayPort to alternate mode for its downstream ports. USB4 hosts need to support both encapsulated and alternate modes in the downstream ports. The idea is that if a display device does not want to implement any other non USB 2.0 peripherals (2.0 has dedicated lines so it can support those), it can implement only alternate mode, (and not need to support the complexities of encapsulating USB4), plus all USB4 hosts needing to support DisplayPort means you know you can connect such a screen to any USB4 device and have it work (although supporting multiple screens like this is optional). One thing to not though is that DisplayPort alternate mode has the option of reversing the device->host wires of USB-C lanes and thus get 4 lanes of host->device data, for 80Gbps at Gen 3 speeds if using both lanes. USB4 V1.0 does not support lane reversal, and USB4 V2.0 can reverse only one bidirectional lane, since it still needs to support device->host data. I think this lane reversal is only possible when using the new new Gen 4 speeds, which provided 80Gbps symmetric, or 120/40 Gbps asymmetric.
vel0city 3y ago
It allows it, but can you actually buy any products for it? https://www.notebookcheck.net/The-demise-of-HDMI-over-USB-C-Alt-Mode-and-more-power-in-cables.680552.0.html https://www.notebookcheck.net/The-demise-of-HDMI-over-USB-C-... > True USB-C to HDMI adapters are no longer going to be a thing. The HDMI Alt Mode is more or less history, and DisplayPort has won. Notebookcheck spoke to HDMI LA and the USB-IF about it. > HDMI LA said that it doesn't know of a single adapter that has ever been produced. Similarly, at the USB Implementers Forum (USB-IF), people who are familiar with the certification process have yet to see a true USB-C to HDMI adapter.
- bandrami 3y ago
  There's an oscilloscope screen that does the conversion in software and was the bane of my existence last year.
- ianburrell 3y ago
  There is also MHL alt mode. The HDMI alt mode was horrible because it used the whole USB-C cable as HDMI cable preventing any other users. MHL is HDMI but over a single pair. My understanding is that all the USB-C to HDMI adapters are using DisplayPort because that is more widely supported by devices. And the conversion chips are just as cheap as MHL to HDMI.
- mr_toad 3y ago
  > have yet to see a true USB-C to HDMI adapter Not sure what this article means. I have a USB-C to HDMI adapter (made by Apple) and a USB-C to HDMI cable and both work.
  - ThatPlayer 3y ago
    The article talks about how adapters like yours use the DisplayPort Alt Mode protocol and then have a DP to HDMI adapter integrated. Rather than implementing the HDMI Alt Mode protocol which also works over USB-C.
jdiff 3y ago
The article mentions the death of HDMI altmode. Is it actually widely supported?
- jsheard 3y ago
  It seems not, I missed that HDMI altmode is still stuck at HDMI 1.4 and they're not making any attempt to bring it up to HDMI 2.0. DisplayPort indeed won in that case.
Zekio 3y ago
no vendors implemented it, so whenever you are currently doing hdmi over usb-c it is actually hdmi over dp over usb-c
- johnwalkr 3y ago
  Which is fine and should stay well-supported because HDMI is also here to stay. The trend for TVs is to include HDMI ports but no displayports.
babypuncher 3y ago
The problem is these two competing standards solve overlapping but distinct problem sets. DisplayPort was designed to be used for computer monitors, while HDMI was designed for home theaters. This may not seem like a very meaningful distinction to most people, but it would become readily apparent to anyone trying to design a home theater around DisplayPort instead of HDMI. Off the top of my head, DisplayPort lacks any equivalents for ARC, Auto Lipsync, and CEC. Odds are your home theater makes use of at least two of these features, even if you don't realize it.
deleted 3y ago
[deleted]