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Displayport: A Better Video Interface

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Re: Displayport: A Better Video Interface

#191

Post by akvadrako »

chrisco255 wrote: post #141
_kb wrote: post #124

Earlier quoted context omitted.

Because (consumer) ethernet is low bandwidth compared to whats needed for video. DisplayPort 2.0 provide a 80Gbps link. HDMI is 48Gbps. Both already use DSC which is a mezzanine compression as this is already saturated for immediate needs. Ethernet is absolutely used for media transport outside of the consumer space. Particularly where there's a need to distribute signals further than what DP or HDMI can provide. The…

The current Ethernet spec supports up to 1000 Gbps, but I think 40 Gbps is about as fast as you can find on the market right now. They could build multi Gbps wifi routers too, it's just not common in the consumer market.

Even 10Gb ethernet isn't suitable for consumers. 40Gb is practically only fiber which has never been successful in homes since it requires more careful handling.

Re: Displayport: A Better Video Interface

#192

Post by ComputerGuru »

bee_rider wrote: post #3

I just like the little retaining clips, and the satisfying little click you hear/feel when plugging them in.

It’s a problem when the x16 slot is the bottom-most and the orientation is such that the clicky thing you must depress is on the bottom side of the DP connector when plugged in, and your case has a ledge after the PCI slots so you cannot realistically depress the latch.

Of course, no one would realistically encounter a case/GPU/cable combo like that. Right?

Re: Displayport: A Better Video Interface

#194

Post by NewJazz »

pdmccormick wrote: post #169
dylan604 wrote: post #164

Earlier quoted context omitted.

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 mo…

Do the USB devices have comparable round trip latency? That is where USB really hurts and where the Thunderbolt audio interfaces seem to fond their niche today.

I'm looking forward to audio interfaces that can do USB4 wrapped PCIe, but for now I live with the latency on Linux.

Re: Displayport: A Better Video Interface

#195

Post by ShadowBanThis01 »

pavlov wrote: post #154
TazeTSchnitzel wrote: post #143

The amazing thing about DVI, and by extension HDMI, is that it's just VGA but digital, with all the timing and synchronisation complexity that implies. Recall that DVI can have both an analog (VGA/DVI-A) and digital (DVI-D) signal in the same cable. They aren't independent; they share some pins and have the same timing. You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if any…

I was guessing that the oddly beautiful 17” Apple CRT Studio Display [1] from 2000 might have been a CRT that used a digital signal cable because it had the short-lived Apple Display Connector, but apparently ADC carried analog too. [1] https://everymac.com/monitors/apple/studio_cinema/specs/appl...

The ADC carried power, too, which is why Apple went with it.

Re: Displayport: A Better Video Interface

#196

Post by MisterTea »

TazeTSchnitzel wrote: post #143

The amazing thing about DVI, and by extension HDMI, is that it's just VGA but digital, with all the timing and synchronisation complexity that implies. Recall that DVI can have both an analog (VGA/DVI-A) and digital (DVI-D) signal in the same cable. They aren't independent; they share some pins and have the same timing. You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if any…

> You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if anyone ever did.

From memory IBM offered a crt with DVI.

Re: Displayport: A Better Video Interface

#197

Post by jsmith45 »

masklinn wrote: post #30
hadrien01 wrote: post #11

Earlier quoted context omitted.

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.

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).

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.

Re: Displayport: A Better Video Interface

#198

Post by ShadowBanThis01 »

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…

It wasn't that short-lived. All DV cameras had FireWire. Although Sony, per its mania for undermining industry standards, created a bastardized version (called I-Link, ugh) whose connector lacked power and required a physical adapter.

External FireWire drives (like LaCie's) were popular for quite a long time, since they required no extra power source.

Re: Displayport: A Better Video Interface

#199

Post by metaphor »

Veliladon wrote: post #17

HDMI predates DP by 5 years, switching wouldn't enable any specific use case, and that 5 years head start means HDMI has market inertia. Yes we should use it because it's better but the practicality? There's so much gear that's HDMI that would have to be replaced or require new active adaptors. It's so much industry and consumer effort for such a marginal gain.

> HDMI predates DP by 5 years...

- HDMI v1.0 initial release = 2002-12-09

- DisplayPort v1.0 initial release = 2006-05-01

To be sure, just under 3.5 years; HDMI rolled into v1.3 a month after DisplayPort v1.0 saw the light of day. Agreed on the impact of market inertia.

Re: Displayport: A Better Video Interface

#200

Post by madars »

TazeTSchnitzel wrote: post #143

The amazing thing about DVI, and by extension HDMI, is that it's just VGA but digital, with all the timing and synchronisation complexity that implies. Recall that DVI can have both an analog (VGA/DVI-A) and digital (DVI-D) signal in the same cable. They aren't independent; they share some pins and have the same timing. You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if any…

This also has side-channel implications, and is a reason why eDP is recommended in voting applications. https://www.eerstekamer.nl/nonav/overig/20160428/richtlijnen...

>DisplayPort uses a scrambler as part of its line encoding in order to flatten the Fourier spectrum of its emissions and suppress spectral peaks caused by particular image contents. This reduces the chances of any particular image content causing a problem spectral peak during SDIP-27 and EMI spectrum measurements. According to the standard, the scrambler reduces spectral peaks by about 7 dB. As a side effect, the scrambler also makes it far more difficult, probably even impractical, for an attacker to reconstruct any information about the displayed image from the DisplayPort emissions. [..] DisplayPort uses a small number of fixed bit rates, independent of the video mode used. Unlike with most other digital interfaces, video data is transmitted in data packets with header and padding bytes, and not continuously with a television-like timing. As a result, DisplayPort cables are not a common source of van-Eckstyle video emanations and this again will make it very hard for an eavesdropper to synchronize to the transmitted data.

Speaking of which: how does one force HDCP (say, in Linux)? That would transform this technology from a DRM nuisance (strippers easily available on AliExpress) into a Van Eck-countermeasure.

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