Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Displayport: A Better Video Interface

hackaday.com

Post reply on HN
Print view View original

161–170 of 426 posts

Re: Displayport: A Better Video Interface

#161

Post by hot_gril »

Aaargh20318 wrote: post #153
Aaargh20318 wrote: post #132

Earlier quoted context omitted.

Why is it nicer? What is the use case for having unreachable windows?

But my windows aren't getting messed up, once I turn the monitor back on it restores the previous state. And the use case is simple: I have 2 monitors hooked up to my machine but I don't always need 2 monitors. I have a 34" 5k2k ultrawide and a 27" 4k in portrait mode. When I'm coding or using my computer for an extended amount of time I turn both on, but when I just want to quickly write an e-mail I only turn on the…

This seems like a very specific situation, and you could disconnect the second monitor for it.

Not sure about the reliability of window restoration. It's at least better in the latest macOS than in older versions.

Re: Displayport: A Better Video Interface

#162

Post by aidenn0 »

xienze wrote: post #101
aidenn0 wrote: post #90

Earlier quoted context omitted.

Sounds like the real question is why don't people use DP for p2p networking links...

There’s nothing magic about DP cables, they’re just typically a short-ish length, which is why they can be high bandwidth and relatively cheap. Once you get to a decent length, the cables get really expensive because you have to put optical transceivers on either side. I have a 25 foot DP cable which cost over $100, for example. So you could do a short length, high bandwidth Ethernet cable, I’m sure. But the reason w…

Yeah, my original comment was based on the "100x more expensive" assertion. a 5m DAC cable is $40 on Amazon, and 25GBe cards can be had for under $200. I think it's probably more than $2.40 for just a 5m DP cable, so 100x was a gross exaggeration.

Re: Displayport: A Better Video Interface

#163

Post by jbverschoor »

muhammadusman wrote: post #50

This post was informative and I didn't realize just how different DisplayPort is from HDMI. Recently, I got a desktop dock that uses DisplayPort instead of HDMI to connect to my monitor. My monitor has 2 HDMI ports, 1 Type-C, and 1 DisplayPort. So far things have been fine but I did notice that the audio is choppy no matter what I do. I thought it was the dock but audio going from my computer > dock > my webcam's spe…

Same here with an lg monitor on dp

Re: Displayport: A Better Video Interface

#164

Post by dylan604 »

hot_gril wrote: post #139
tshaddox wrote: post #123

> However, I’d like to tell you that you probably should pay more attention to DisplayPort – it’s an interface powerful in a way that we haven’t seen before. Lines like that really show just how long it can take for standards to get on the radar of mainstream tech culture. I remember hearing about and being excited about DisplayPort's move to packetized digital video in college in 2008, and seeing the first Macs with…

That, and a similar line might've been said about FireWire, which didn't really make it.

Maybe I agree with that, but I also know that firewire helped usher in the digital video era. It allowed the transition from tape based acquisition when media cards were prohibitively expensive. Audio/Video/Deck control all down one single cable straight from the camera to the computer was what really kicked the prosumer market into being able to lean closer to pro than consumer. Now that media cards are actually affordable, that does seem like ancient history. I could see how you might think of firewire as a failure if you're looking at it as a USB type transition, but for the camera/video professions, it served a very good purpose even if short lived

Re: Displayport: A Better Video Interface

#167

Post by drbawb »

AlotOfReading wrote: post #156
xxpor wrote: post #117

Earlier quoted context omitted.

I'm 90% sure it was, but it looks like they did a major UI update to the site so it's not triggering the "that was it!" lightbulb in my brain.

I use one, so I can confirm they work extremely well, subject to some caveats: * The total cable length is important, both between the host / KVM and the KVM / monitor, as well as any daisy chained displays you have. I had to use certified cables to get everything working reliably with my setup. * There's a weird interaction with BIOS power on. The boot display drivers I have freak out if they aren't the active displ…

>There's a weird interaction with BIOS power on. The boot display drivers I have freak out if they aren't the active display and fail. I solve this by switching the KVM before I turn the computer on. After everything is booted into an OS, it works fine to switch.

Do you have an AMD GPU by any chance? I have the level1tech 2-head DP 1.4 KVM, with an AMD RX 560 on a Linux host, and after updating to kernel 6.4 recently my computer now boots fine without a monitor attached.

I had a similar issue where a display had to be _on_ and _connected_ (i.e: active on the KVM) at boot time, or the GPU wouldn't work at all. I could get in via SSH, so I tried various amdgpu recovery options, poking the device to reset it, reloading the kernel modules, etc., and never had any luck. I just lived with the quirk. It was problematic because if you left home with the KVM selected on the Windows guest, and needed to reboot the Linux host remotely, you'd come home to a non-functional Linux desktop.

Re: Displayport: A Better Video Interface

#168

Post by chx »

> However, if you don’t need the full bandwidth that four lanes can give you, a DP link can consist of only one or two main lanes resulting in two

This is how many USB C docks operate. The USB C connector also has four high speed lanes and there's a mode where two are assigned to carry DisplayPort data and two are assigned to be TX and RX respectively for USB. Until DP 1.4 appeared, this meant you were quite limited in display resolution if you didn't have Thunderbolt and wanted faster than 480mbps data speed. With DP 1.3, two HBR3 lanes can carry 12.96 Gbit/s which is almost exacly the requirement for 4k @ 60Hz at 12.54 Gbit/s. DP 1.4 adds compression on top of this. One more beauty of DisplayPort is it's point to point so it's entirely possible your USB C hub will carry the display data from the host to the hub as compressed HBR3 data over two lanes and then hand it out to two monitors over four uncompressed HBR2 lanes to each so a modern USB C hub can, without Thunderbolt, drive two 4k @60Hz monitors and still provide multiple gigabit speed data. It's a very neat trick. This needs full DisplayPort 1.4 support including DSC in the host, for integrated GPUs in laptop CPUs this means AMD Ryzen 4000 and newer or Intel Tiger Lake and newer (older laptops with discrete GPUs might have had it, too).

Handy tip: if your hub is DP 1.4 and drives multiple monitors then it's most likely using a Synaptics MST hub to do this (almost all non-Thunderbolt ones do and many Thunderbolt ones as well) and Synaptics provides a very very little known diagnostics tool called vmmdptool (available in the Windows Store). It doesn't replace a full DP AUX protocol analyzer of course but it's free and for that price it's really handy.

This topic is dear to me because I have fixed the USB C specification related to this and allow me to be damn proud of that: it used to erroneously say the USB data speed in this mixed functionality was limited to 5gbps but it is not, the limit is 10gbps. https://superuser.com/a/1536688/41259

Ps.: When I say Thunderbolt, I am well aware of how Thunderbolt 4 is just USB4 with optional features made mandatory. It's not relevant to the discussion at hand.

Pps.: DisplayPort is the native video standard for USB C, C-DisplayPort adapters and cables are basically passive because they just need to tell the host how to configure the connector lanes. Meanwhile all USB C - HDMI cables and converters are active which constantly work on the DP signal to become HDMI. DisplayPort++ alas is not implemented with the USB C connector. For this reason if any compatibility issues arise it's always better to connect a USB C device to the DisplayPort input on a monitor. A HDMI alternate mode was defined in the past but it remained paper only and it has been declared dead this year at CES.

Re: Displayport: A Better Video Interface

#169

Post by pdmccormick »

dylan604 wrote: post #164
hot_gril wrote: post #139

Earlier quoted context omitted.

That, and a similar line might've been said about FireWire, which didn't really make it.

Maybe I agree with that, but I also know that firewire helped usher in the digital video era. It allowed the transition from tape based acquisition when media cards were prohibitively expensive. Audio/Video/Deck control all down one single cable straight from the camera to the computer was what really kicked the prosumer market into being able to lean closer to pro than consumer. Now that media cards are actually aff…

I once purchased a FireWire multi-channel audio interface with the express intent of reverse engineering the protocol in order to add Linux support. I purchased a specialized PCI card that was intentionally non-standard (not OHCI 1394) but could snoop and capture traffic between a device and a host. I chipped away at deciphering a register map for awhile, but eventually better USB audio devices came along that had more driver support.

Still trying to do the same sort of thing though with some audio related USB and Ethernet/IP devices so I guess I never really gave up the idea in my heart!

Re: Displayport: A Better Video Interface

#170

Post by Night_Thastus »

gjsman-1000 wrote: post #29
nfriedly wrote: post #25

I'm annoyed nvidia for putting the current generation of HDMI on their recent GPUs, but leaving them with an outdated version of DisplayPort. For a long time, my advice to anyone was to always choose DisplayPort whenever it was an option. But now that has to have the caveat of "if you have a new high-end GPU and a fancy high refresh rate monitor, HDMI might actually be better for your situation"

> I'm annoyed nvidia for putting the current generation of HDMI on their recent GPUs, but leaving them with an outdated version of DisplayPort. That was due to unfortunate timing where HDMI had the specifications ready before DisplayPort did.

I thought it was because their G-Sync modules had not been updated to support the new DP? That was what I heard.
Post reply on HN