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USB 4 Version 2 - 80gbps

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pastrychef said:
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I strongly believe that Thunderbolt's fate will end up being the same as Firewire's.

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I have a bunch of FW audio devices that I still use for my personal recording jokes. Anywho, the FW is used via my FW PCIe cards. So far, so good.
 
UtterDisbelief said:
Can you imagine the confusion the different cables will cause?
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No need to imagine. Vendors never agreed on any consistent scheme for USB-A. Pure USB 2.0 ports tend to be black these days, but not always. Basic USB 3.x ports tends to be blue, but not always. Other colours (teal, red, gold) tend to promise higher speeds, but with no consistency whatsoever. The box full of USB cables I've gathered over the years is… er… forget it.
I've yet to meet a USB-C cable with speed and/or power labelling.

So it's a safe bet that vendors will make USB4 version-whatever a hot mess of 5/10/20/40/80 Gbs speeds. (20 Gbs is the only speed that is guaranteed by the specification, but a wrong cable could still ruin it; 40/80 Gbs are for marketing.)

UtterDisbelief said:
Not to mention the high cost. Right now USB-C 3.2 Gen 2 fully connected cables are not cheap. What will a 240W cable be? Will it need to be very short if passive and active if long?
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Short: Passive / Long: Active. I'd guess so. And 240W will always be short because "long" will go optical inside.

If I wanted to ensure that a USB4 chain works at the advertised speed, I'd be tempted to buy a Thunderbolt 3 or 4 cable: Certified, and labelled.
Which perhaps points to a path to success and survival—as an elite niche product only!— for Thunderbolt: Pay more to select vendors, get certified items which work at the advertised speed. As opposed to the USB model: Get cheap items from wherever, plug as you feel and test your luck with the performance you get today. Plug and Pray.

UtterDisbelief said:
It's great that the standards are being pushed to greater heights, but to be commonplace the complexity needs rationalising. And in a way maybe a new port design would be "kinder" to the end-user because you would know where you stood.
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Yes! Bring in "USB connector, type D"! :mrgreen:

torchon-shadoks-pourquoi-faire-simple-ecru-48-x-72-6964010000.jpg

("Why make it simple when one can make it complicated?!")
 
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c-o-pr said:
The way I read it, there's no reason at all for concern of TB to die: it already got completely merged into USB4.
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Not quite: USB4 incorporates, and is compatible with, Thunderbolt 3; but Thunderbolt 4 is a more advanced spec and can do things which USB4 need not do (multiple monitors, PCIe tunnelling) or cannot do (VT-d, PCIe@32GBs).

So there is room for Thunderbolt 5 to develop, catch up with the USB4 v.2 data rate and possibly add further capabilities. I suppose it depends how much interest Intel has in keeping Thunderbolt (and its paid-for certification scheme) ahead of USB.

c-o-pr said:
Let's see I just plug my tonymacx86 bat cave post generator dongle into this usb port here, and... Doh! I didn't map that port as type 65535, garrr!
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Geek alert. Code 0xFF0000! :lol:
 
etorix said:
Not quite: USB4 incorporates, and is compatible with, Thunderbolt 3; but Thunderbolt 4 is a more advanced spec and can do things which USB4 need not do (multiple monitors, PCIe tunnelling) or cannot do (VT-d, PCIe@32GBs).
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Thanks for mentioning the certification feature list distinction. When I combine this list with the following observations from ArsTechnica article:
Jeff Ravencraft, president and COO of USB-IF, told Ars that USB4's multi-monitor support depends on the computer "and is a question of how many streams a host can support, but "from a bandwidth perspective, the maximum is four 1K monitors at [a refresh rate of] 120 Hz, two 4K monitors at 120 Hz, and one 8K monitor at 30 Hz."
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IOW technically USB4 does multi monitor but its most common instance 20G lacks bandwidth and corresponds with typical lane allocations for PCs (2x PCIe gen3) in the era it was released, where historically every PC is PCIe lane limited with configuration balances that target to market segments.

As to PCIe tunneling, this is subject to previous point targeting a laptop form-factor specific capability, again inherently subject to computer maker.

VT-d is Intel specific IO capability.

Each of these so-called "missing" features from USB4 is in a design domain beyond the purvey of the USB-IF. They're in the purvey of a computer makers forum!

And now we see why there's no TB4 in Macs, because TB4 is certified by Intel and released after transition to AppleSi. So if there's cause for alarm about TB future in Mac, the klaxon should already been going off since 2021.

Complexity is a fair gripe nonetheless, but it's too easy to overlook the good reasons for it.

The TB vs USB comparison seems like a red herring.

You know, maybe U.S. never should have broken up Bell, and we'd be web surfing on modems with optical couplers to black-Bakelite wired telephones with 1000-year service life and 24/7 operator assistance.

The problem with a made world must always be "why did they make it like that?"

But there's some hope it could just as easily be made another way.

Except for rising seas... fire, flood, pestilence, famine — nuclear armageddon — and other eventualities of biblical proportion.
 
c-o-pr said:
You know, maybe U.S. never should have broken up Bell, and we'd be web surfing on modems with optical couplers to black-Bakelite wired telephones with 1000-year service life and 24/7 operator assistance.
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Competition would've come from cable and international carriers. Even after being broken up, the baby Bells still tried to make use of the copper twisted pairs until it became evident that they couldn't compete with cable.
 

Notable points:
  • Thunderbolt 4 seems to be essentially just USB4 with all optional items implemented (but USB4 is more like TB3 than USB3...).
  • Displayport dualmode (aka DP++) allows sending out HDMI/DVI signals from a displayport connector. This essentially just repurposes pins on the DP connector to transfer HDMI/DVI signals, so can be used with a passive adapter or cable (though the adapter does need to do voltage level shifting). This only works to connect a DP source to a HDMI/DVI sink (display), not the other way around. This also repurposes two additional CONFIG1/2 pins from being grounded to carry HDMI/DVI signals, so dual-mode is not available on an USB-C DP alt mode connection. [source]
  • Active cables typically seem to be geared towards (and/or limited to) a particular signalling scheme and/or direction. This means that they are usually not usable for protocols they are not explicitly designed for. This partially comes down to the bitrates used, but also the exact low-level signalling protocol (e.g. USB3 Gen2, USB4 Gen2 and DP UHBR 10 all use 10Gbps-per-line, but use different encodings, error correction and/or direction, meaning active cables might support one, but not the other).
  • Passive cables can generally be used more flexibly, mainly limited to a certain bitrate based on cable quality and length.
  • Cables can also contain a "e-marker" chip that can be queried using USB-PD messages on the CC pin, containing info on the cable's spec. Such a chip is required for 5A operation (all other cables are expected to allow up to 3A) and for all USB4 (even the lower-speed 10Gbps-per-line USB4) operation.
  • Cables with "e-marker" chip but no signal conditioning are still considered passive cables.
  • USB4/TB4 requires an e-marker chip in the cable (falling back to USB3 or TB3 without it). Passive cables (including passive TB3 cables) can always be used for USB4 (with the exact speed depending on the cable rating), while active cables can only be used when they are rated for USB4 (so active USB3 cables cannot be used for USB4, but active USB4 cables can be used for USB3). [source]
  • USB-C uses the CC pins for detecting a connection and deciding how to set it up. A host (or dowstream facing port or sourcing port) has pullups on both CC pins (value depens on available current), a device (or upstream facing port or sinking port) has pulldowns on both pins (value is fixed). Together this forms a voltage divider that allows detecting a connection and maximum current. A cable connects only one of the CC pins (leaving the other floating, or pulling it down with a different resistor value) which allows detecting the orientation of the cable. [source]
See long list of USB-C Alt modes in article, this stuff is really complicated.

See even longer list of USB4/TB4 details, even more complicated, my god.

  • TB1/2/3 were propietary protocols, implemented only on Intel chips. USB4 (and also TB4) are (somewhat) more open and can be implemented by multiple vendors (though I could find the USB4 spec easily, but not the TB4 spec, or the TB3 spec which is required for compatibility, or the DP alt mode spec, which is required for USB4 ports).
  • Different USB3/4 transfer modes have been renamed repeatedly (i.e. USB3.0 became USB3.1 gen1 and then USB3.2 gen1x1). Roughly, gen1 (aka SuperSpeed aka SuperSpeed USB) means 5Gbps-per-line, gen2 (aka SuperSpeed+ aka SuperSpeed USB 10Gbps, or SuperSpeed USB 20Gbps aka USB4 20Gbps for gen2x2) means 10Gbps-per-line, gen3 (aka USB4 40Gbps) means 20Gbps per line. No suffix or x1 means using only one pair of lines, x2 means two pairs of lines (so e.g. gen2x2 uses all four lines, at 10Gbps-per-line, for 20Gbps full-duplex and 40Gbps of total bandwidth). Also, you can mostly ignore the USB versions (i.e. USB3.1 gen1 and USB3.2 gen1x1 are the same transfer mode), except for USB4 gen2, which is also 10Gbps-per-line, but uses different encoding. [source]
Here's some hints on HW discovery:
  • On Linux, to get some basic info on present TB controllers and devices and the used link speed, you can use boltctl (e.g. boltctl list -a).
  • To see what interfaces are present on e.g. a TB dock, run echo "module thunderbolt +p" > /sys/kernel/debug/dynamic_debug/control, plug in your dock and check dmesg (which will call the USB4 controller/router in the the dock a "USB4 switch" and its interfaces "Ports").
There's 100x more in the article.

Enjoy the mayhem!
 
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