
USB4 Specification - ingve
https://www.usb.org/document-library/usb4tm-specification
======
CobrastanJorji
Reading through this, I'm left unable to see the underlying forces. None of
the people working on this spec are idiots, so how did they arrive here? What
are the forces and unstated requirements behind the scenes that I don't
understand that have led to a USB4 spec with this many potential flavors and
absurd naming conventions to express them? Is it something about cost? Or
patents? Or some random company who won't budge on something but needs to be
included?

~~~
msbarnett
> Is it something about cost?

It's _hugely_ about: cost, and the desire of the USB forum to ship a single
"does everything" protocol that keeps a large chunk of the industry from
choosing to stay on some old version of the spec forever.

Tons and tons of manufacturers of cheap low end devices out there aren't
willing to replace a $0.10 USB controller with something that costs 30x as
much when they have no need for the high-end speeds of Thunderbolt 3, fast
charging, DisplayPort alternate modes, etc. Consequently the spec can either
contain a lot of optional features they can choose to ignore, or it can
mandate support for all of the 40 Gbps active cable fast charging etc options,
and watch as devices partition themselves between the few the need all of that
stuff, and the majority that ship simple micro-USB 2.0 hardware.

If they did the latter, then USB 4 is essentially pointless: that's the exact
situation we were already in 5+ years ago, except the cheap side was called
"USB 2" and the expensive side was called "Thunderbolt". All we've done is
rename the expensive side to "USB 4".

If they do the former, they ship a "spec" so full of options that it's already
nearly impossible to tell exactly what devices or features any given USB C
port will support without recourse to a specifications sheet.

Fundamentally, "one port and protocol to rule them all" is probably just a bad
idea. Trying to serve the needs of both cheap slow devices and expensive fast
ones puts the forum in a contradictory position, and the only "benefit" from
combining the standards that serve each niche is opaque ports and cables that
consumers can't easily reason about the compatibility of.

~~~
jayd16
>Fundamentally, "one port and protocol to rule them all" is probably just a
bad idea

I disagree. The situations are:

1)ports are the same, protocol match : works

2)ports are the same, protocol mismatch : won't work, some user confusion

3)ports are different, protocol match : could work but won't without an
adapter

4)ports are different, protocol mismatch : won't work. Adapters might exist
but those won't work either.

I'd much rather deal with situation 2 over 3 and 4. Display adapters already
have situations where you can get adapters to cobble together DVI and VGA
ports but still fail to get a proper connection, so its not really a fix
anyway.

The USB foundation should just come up with better branding around what kinds
of things a port supports. No reason we can't have a thunderbolt icon next on
a USB port. Its strictly better than a new physical port, IMO.

~~~
chrisweekly
Pardon my ignorance, but isn't (2) really dangerous when it comes to things
like power delivery?

~~~
izacus
No, because power delivery is negotiated from a safe USB1 type base levels. If
the device doesn't request it, it won't get delivered.

The only outliers are moronic implementations like Nintendo, where they ask
for capabilities, receive the charger capabilities and then just start pulling
power at hardcoded levels even if the charger doesn't specify it supports
those power levels. But there's nothing you can do against that - you even
with different port shape, a broken implementation can still fry your device.

~~~
sschueller
Didn't the charger from the Pixel not implement this correctly and send full
power down the line even if a device can't handle it?

~~~
ProZsolt
The Pixel charger was fine AFAIK. The Nexus 5x and 6P had rogue chargers

------
gumby
The real crimes are:

1 - non-mandatory labeling. What does a given port support? What about a given
cable?

2 - the name "USB4 Gen 3×2". Honestly I have never had the faintest idea what
any of the various absurd names invented by the USB IF might mean. Superspeed?
High speed? USB 3.1?

~~~
burnte
Oh, it's very simple.

USB 3.0 was renamed to 3.1, but that was confusing, conflicting with USB 3.1,
so it was rerenamed to USB 3.2 Gen1, so that people understood that 3.0 was
ACTUALLY the first generation of USB 3.2

But that caused problems with USB 3.1, which was faster than USB 3.2 Gen1, so
it was renamed USB 3.2 Gen2, so that it crystal clear was faster than USB
3.0/3.1/3.2 Gen1.

But that caused problems with USB 3.2, because 3.2 is just two lanes of USB
3.2 Gen2, so 3.2 was renamed to USB 3.2 Gen2x2 so people knew it was TWICE as
good as USB 3.2 Gen2.

The problem now is that USB4 eliminates all that clarity, so right now the big
marketing push is to clarify it as USB 3.2^2 Gen1: The Reckoning.

To resolve the conflicts of historical naming with USB 1 and 2, those will be
renamed USB 3.2 Gen √0 and USB 3.2 Gen √-1/pi.

~~~
Dylan16807
You got some of that mixed up.

First there was USB 3.0. Technically the standard included older speeds, but
people called the new one "3.0" and all was good.

Then 3.1 came out. But what about the poor manufacturers with 3.0-speed ports?
Well, someone decided they could call those ports "3.1 Gen 1".

And it was all downhill from there. 3.1 Gen 1 became 3.2 Gen 1, and now
becomes USB4 Gen 1. They added more "Gens", even ones where the word
"generation" makes no sense. Now the number tells you nothing about speed, and
there are two separate nomenclatures for speed that are both confusing.

And I'm _still_ not sure if they did or did not ever implement Gen 1x2...

(It being USB4 instead of USB 4.0 is another stupid poke in the eye on top of
everything else.)

~~~
dbtx
> being USB4 instead of USB 4.0 is another stupid poke in the eye

This. I wish to nominate the lot of it for BJAODN

------
Dunedan
When the USB-IF announced that they're going to incorporate Thunderbolt into
USB4 I already worried that this might further complicate USB hardware and
software.

Turns out: My worst nightmares just became true. We now have running USB over
Thunderbolt. I don't even know where to start facepalming about this
clusterfuck.

Take DisplayPort for example: Up to now we had the DisplayPort alternate mode
for USB-C. That just worked for most devices with USB-C. Now we also have the
tunneling of DisplayPort over Thunderbolt (as Thunderbolt-enabled Macs offer
since Apple introduced Thunderbolt in its devices and which they use when
connecting to Thunderbolt-enabled monitors). Both methods seem to be optional
for USB now, so in future a host and a peripheral device might support
"DisplayPort over USB", but while one might only supports the USB-C
DisplayPort alternate mode, the other one might only support DisplayPort
tunnels over USB4, causing them not to be able to talk DisplayPort to each
other.

I guess I'm going to facepalm for a few hours now, while I read the
specification in more detail.

~~~
Dunedan
> A USB4 host and USB4 peripheral device may optionally support TBT3
> -Compatability.

That sounds good from an implementors point of view, but offers another area
of possible incompatibilities for connecting USB4 and Thunderbolt 3 devices.
Imagine both devices support tunneling DisplayPort signals, but the USB4
device doesn't support the Thunderbolt 3 compatibility layer: As in the
example before they won't be able to establish a DisplayPort connection, while
other USB4 devices, which offer Thunderbolt 3 compatibility might.

~~~
tenebrisalietum
How is this better than VGA again?

~~~
jandrese
VGA has the downsides of the analog signal, like ringing and smearing when you
have a higher resolution running over a long cable.

DVI ended up being kind of a mess with the different connector types and
ultimately fairly limited digital bandwidth.

Displayport is pretty good except everything Displayport costs 50% more than
it should.

~~~
Izkata
DisplayPort also seems to randomly stop working, requiring
unplugging/replugging the USB to reset it. Occasionally I'll even boot up one
morning to find it's not working at all and something or other needs to be
reinstalled.

------
perlgeek
As a consumer, can I please have a standard where I don't have to chase a new
version every few years?

I know that many are backwards compatible, but they aren't forward compatible
-- my MicroUSB cables don't help at all with USB-C, and type A and B
connectors are still around.

By the time all of my micro USB devices have disappeared from my household,
I'm sure a new thing will have emerged that's incompatible with USB-C, and so
I'll still have to have several different cables around.

~~~
userbinator
The industry has decided that it is more profitable to make you buy adapters
or a new device every couple of years (and create more e-waste in the
process), hence the accelerating churn. And each new revision of the standard
will introduce its own set of problems, guaranteeing them something to do for
the _next_ revision after that; but the churn situation with USB isn't
actually that bad:

    
    
        USB 1.0 - 1996
        USB 1.1 - 1998
        USB 2.0 - 2000
        USB 3.0 - 2008
        USB 4.0 - 2019
    

Also, the vast majority of devices are still 1.x/2.x speed, so it might be
more of a diminishing returns type of situation.

~~~
jdnenej
Appart from storage and video, there is just no need to go over USB 2.0. My
brand new USB microphone uses USB 2 because there is no advantage at all to
USB 3.0 for this device.

~~~
larkeith
I have a single USB 3.0 external hard drive. Everything else is USB 2.0. It's
fantastic, I never have to worry about whether I have the right cord or if the
device supports it, and in the rare case where I need to transfer a file large
enough that sending it over the Internet would be a bottleneck, I just toss it
on the external HDD.

------
Havoc
Please father Christmas may I just have one present?

A standard that is actually standardized in practice.

To this day I still don't know exactly how to buy a cable for my raspberry pi
4s. (Yes more a USB c than USB 3 issue but you get my point - a standard that
isn't standardized fails at it's raison d'etre)

~~~
imtringued
Just buy the official power supply. It's probably better than whatever cheap
junk you've intended to abuse your Raspberry Pi with.

~~~
ProZsolt
Actually cheap junk will work, but any quality charger(eg. Apple) with emarked
cable won't.

------
MBCook
Good. USB3 is still a mess, better make a new one before that gets sorted out.

~~~
AceJohnny2
USB4 is basically Thunderbolt 3, i.e. USB3.x + PCIe + DisplayPort.

See the diagram in the linked spec, "Figure 2-1 USB4/USB3.2 Dual Bus System
Architecture"

~~~
djsumdog
I remember hearing that on .. Dave2D I think? Or Linus Tech Tips .. one of
them said USB4 is Thunderbolt 3.

I assumed the standards were just combining and the two would be equivalent
protocols, but I assume that's not true then? Does USB4 basically just add
PCIe onto the USB bus? How will that work with AMD board that still don't
officially have Thunderbolt/PCI Hotplug support?

~~~
AceJohnny2
> Does USB4 basically just add PCIe onto the USB bus?

Yes. Which is kinda what Thunderbolt 3 does (except encapsulated in the TB
packet format, not USB).

The silicon world has been gradually converging on its Serializer-
Deserializer/PHY technology. I don't know quite the family history, but I
believe the PCIe PHY is very similar to USB3 which is identical to Thunderbolt
3.

Since the link layer was the same, it was then "just" a matter of protocol
design to make everything just use the same link. And that's how you got
Thunderbolt 3 / USB 4.

~~~
tarheelredsox
PCIe uses different rates than USB, but both at their basics use NRZ (Non-
Return to Zero) [https://en.wikipedia.org/wiki/Non-return-to-
zero](https://en.wikipedia.org/wiki/Non-return-to-zero). The bigger
differences are in the channels they target. The channels characteristics
drive the complexity of the signal processing circuitry required (eg Power and
Cost) in the PHY devices. Hope that adds a bit of clarity to your PHY
question.

------
squarefoot
The more I look at the USB mess the more I feel that a revised faster Ethernet
with provisions for both insulated and direct connections (magnetics-less ==
cheaper chipset, lower power consumption etc) for board to board
communications then a smaller/sturdier connector plus PoE built in would solve
every problem USB tried to solve including the ones it introduced.

------
AceJohnny2

        Apple Inc. 
        Hewlett-Packard Inc. 
        Intel Corporation 
        Microsoft Corporation 
        Renesas Corporation 
        STMicroelectronics 
        Texas Instruments
    

Honestly, I'm a bit surprised at how short this list of authors(?) on such a
wide-impact standard is. Where are other silicon designers? Where's Synopsys,
or Mentor Graphics (who often provide the Hard IP used by chip designers)?
Where's Qualcomm or Samsung? What about Google, for Android?

 _Edit:_ actually reading a bit further to the "Acknowledgement of Technical
Contribution", this is the list of _promoter_ companies. The contributors list
is _way longer_ and includes everyone you'd expect.

~~~
Zhenya
Look further down. You showed just the promoters list, there is a much longer
contributors list.

Google and Samsung are both there.

------
pvorb
Why does USB have two seemingly unrelated versioning schemes? There's USB 1,
2, 3 and now 4 as well as Type A, B and C. This mess looks like manufacturers
wanted to create a way to trick the average customer into buying the wrong
cable or adapter, whereas initially the reason for creating USB was to
increase compatibility.

~~~
msbarnett
> Why does USB have two seemingly unrelated versioning schemes? There's USB 1,
> 2, 3 and now 4 as well as Type A, B and C.

They decoupled the standards for the protocol and the connector. "USB C" is
just a port/connector shape -- there's no guarantee that any cable or port
that is USB C shaped supports _any_ version of USB-the-protocol. This is the
case with eg) dedicated Thunderbolt 3 ports and cables.

It's every bit as silly and confusing as it sounds in practice.

~~~
pvorb
And I forgot to mention the mini and micro versions of USB ports, which add to
the overall confusion.

~~~
jdnenej
There is also the USB 3 versions of mini and B which don't fit in the USB 2
ports. This is part of the reason I have an entire draw dedicated to different
USB cables.

------
Causality1
Good job completely failing to address actual problems, USB-IF. What do people
actually need? They need to be able to easily tell what the port on their
device is capable of doing and they need to avoid buying chargers, cables, and
devices that violate the specification, especially when they do so in a way
that might destroy a device or even endanger the user. Unfortunately the only
thing the USB-IF cares about is "Moar megabits! Moar!"

------
andrekandre
probably really dumb question with a really obvious answer that i don’t see,
but...

why not have a packetized protocol like ip over the cable and devices just go
over that? wouldnt things like enumeration, identification,
connect/disconnect, interleaving protocols and encryption be much simpler
since it’s a known domain?

wouldn’t that be more “universal” than cramming usb2, usb super speed, pci-e,
displayport (which afaicr also wraps a few things) etc over a single cable?

am i missing something or is this just a cost issue...?

[edit] slightly answering my own question: pci-e is a packetized protocol...
so i guess cramming everything in is more backwards compatibility to get all
the other connectors subsumed into a single cable...?

~~~
shawnz
USB is packetized. But without those seperate modes of operation, every single
adapter would need a microcontroller in it.

~~~
nightfly
Is that really a problem?

~~~
shawnz
Imagine a world where the reliability of your devices significantly depends on
how much you paid for your USB 3->4 adapter. Is that a better situation than
what we have today?

~~~
TeMPOraL
It already does in terms of USB cables. Buy a wrong cable, and your device
won't charge, or won't charge fast enough, or won't communicate. And you can't
tell the good/correct cable from the bad ones visually.

The standard can have any number of optional modes to be implemented by
devices. I don't care. What I want is for it to have _one_ cable type. Because
it's kind of a point of an universal port that people will use cables from one
device with another.

~~~
caf
It's unreasonable to expect one cable type, because the additional costs for
cables that support very high data rates or very high power delivery are
prohibitive for cheap devices that don't need those.

What they do need to do, though, is minimise the different cable options and
make them easy to distinguish. My suggestion would have been to have a basic
USB-C cable with exactly two optional designations: +FAST and +POWER. It's
then easy enough for a device to say _" this requires a USB-C+FAST cable"_ and
consumers to then look for the same.

------
zbraniecki
Will this bring higher PD? A lot of laptops require 100W-130W of power (see,
Lenovo X1E or Dell 7590), while the highest PD I've seen from usb is the Apple
charger for 86W. I know Dell produces proprietary 130W usb-c charger, but I'm
wondering if usb4 will help make it a standard.

~~~
cesarb
This specification is only about the data bus, not the power bus, since
they're separate in USB-C. So no, this will not bring higher power (and higher
power won't need to wait for a future USB-5 standard).

~~~
zbraniecki
thank you for the explanation! Do you happen to know if there's any work on
bumping the power bus to 130W?

I see that USB PD rev 3.0 allows up to 100W -
[https://en.wikipedia.org/wiki/USB#Power-
related_specificatio...](https://en.wikipedia.org/wiki/USB#Power-
related_specifications)

Is there any work on rev 4?

------
zzo38computer
I think USB is terrible. One problem is that USB addressing is not by the
physical port that it is connected to (among other things, this is a security
problem, but there are many other problems with this too); does USB4 correct
that? Another problem is how vendor codes and that stuff is work; it should
instead be identified by protocol type, and to allow the user to override the
protocol type with the operating system functions.

There is other stuff is better, such as RS-232, and Compact Flash
(unfortunately it lacks a write protect switch; SD has it but only the full
size SD cards and not the smaller size; SD card has other problems though),
and then also add some of my own specifications too, such as IMIDI and Digi-
RGB, and you can have separate ports for each of these four thing.

~~~
h2odragon
"rs232 is better" only if you ignore the incredible mess of horror that has
been committed under the name "rs232". What we have today is only the most
sensible bits that survived 40+ years of ablation in the real world. Even now
its not a great situation: what voltages will your two chips of different
types be able to be use for their "rs232" conversation? TTL? will you need
+/-12v? 15v?

------
holy_city
The Serial Time Link Protocol (STLP) looks really cool to me - I've thought
for awhile that the next-gen in audio gear would be more modular front ends
that sit on top consumer protocols, which is where things are moving in
broadcast/commercial audio installations today. I can imagine a whole host of
consumer and professional devices that solve real problems at lower costs than
we can today. Really interesting stuff.

edit: one weirdness, STLP has a recommended packet rate of 62.5kHz (actual
quote "A Router shall periodically transmit a Serial Time Link Packet on
TMU_CLK_OUT. The period between transmissions is implementation specific, but
it is recommended that a Router transmit a Serial Time Link Packet every 16
μs"). If the only application domain (besides compliance testing) is audio,
how did they arrive at that recommended rate, where it is rather different
from standard sample rates (44.1k/88.2k and multiples of 8kHz)? I'm not sure
how that affects clock synchronization.

~~~
kevin_thibedeau
USB already supports isochronous transfers for audio.

------
boznz
Had to read the USB1 spec in 1998 to make a HID Device using a small micro,
took me over 3 weeks to get it working and was debugging shit for months
afterwards. Would never go there again and for future projects I decided
ignorance was bliss and just used whatever stack the chip designers supplied,
I suspect that covers 99% of all devices out there.

~~~
spancap
Have fun when your product falls on its face because the vendor stack got the
corner cases wrong.

------
Zhenya
So basically, they are attempting to redo the mess that is 3.x

very cool.

"When configured over a USB Type-C® connector interface, USB4 functionally
replaces USB 3.2 while retaining USB 2.0 bus operating in parallel. Enhanced
SuperSpeed USB, as defined in USB 3.2, remains the fundamental architecture
for USB data transfer on a USB4 Fabric"

------
CharlesMerriam2
The Grrranimals standard worked. People would match up symbols to see what
worked together. Why cannot technology do the same? Yes, the cables plug
together, but one has a turtle icon and one has a car icon?

~~~
klausjensen
I am genuinely curious to read more about this, but a google search for
Grrranimals doesn't give me anything to work with. Can you provide a bit more
info, please?

(if this was a joke, consider this my admission of egg on my face)

~~~
spc476
It's "Garamimals". It's a clothing line for very young kids where they can
match the tag on a shirt with a tag on the pants and have an outfit that "goes
together."

------
AceJohnny2
So USB 4 is basically Thunderbolt 3, got it.

(per Fig 2-1 "USB4/USB3.2 Dual Bus System Architecture")

Edit: with Gen3 speeds (20Gbs/link) and with optional Dual-Lane Bonding for
increased bandwidth.

------
baalimago
USB3 and thunderbolt (unsure about their exact relation) enabled eGPU's, which
is very cool.

What will USB4 enable?

------
kaetemi
Is this a universal serial bus, or a universal docking station port?

------
345218435
why the bloody fuck don‘t we get a new, clean thunderbolt bus — as it was
invented by apple/intel — and leave the usb folks play their mindless games?

jesus.

------
aetherspawn
Why not standardise on USB-C and just make -C with the 2 added Thunderbolt
pins (ala Apple) the norm? Why more specs

~~~
ghostly_s
Huh? Apple does not sell any devices with "2 added Thunderbolt pins".

~~~
aetherspawn
Yes they do, USB-C cables with Thunderbolt is different from regular USB-C on
account of the 2 data pins added.

So none of the USB-C cables I bought would enable me to use external monitors
with my hardware because it supported 2 displays over TB only. But the
connectors aren’t even keyed so it’s just an irritating mess to keep track of
what is and isn’t.

However it would be a great system if TB over USB-C was the default and only
probably.

~~~
chx
You are mistaken. Thunderbolt alternate mode does not require any additional
pins, it does require special cabling though. Most Thunderbolt cables are not
capable of any 5-10(-20) gbps USB but they are still using the exact same
connector.

USB 4 will change this in that Thunderbolt cables will now be compatible with
everything.

The only thing you possibly could think of is VirtualLink which _repurposed_
the existing USB 2.0 pins for two more high speed lanes but even that is using
the exact same physical connector.

------
aloknnikhil
Why would they attach this as a zip file? Makes reading on an iPhone
impossible (CORRECTION: cumbersome)

EDIT: Learnt something new. But the spec on an HTML page would be a lot more
convenient than having to install more apps just to read this document.

~~~
OJFord
Is it truly impossible?

No fs access has been one of the things stopping me becoming an iOS user, I
thought it'd make some things harder, but I didn't realise something so
regular seeming (as in I don't have to be a tech nerd to want to open a .zip)
would not be possible.

~~~
theclaw
You can save downloads to the Files app, which then has folders for all the
storage apps you have installed, like dropbox or icloud or whatever. You can
also save to the device local storage, but for some reason only in folders
created by other apps.

~~~
jedieaston
iOS 13 allows you to store any file on your iPhone and unzip/zip it, without a
certain application.

