USBefuddled: Untangling the Rat’s Nest of USB-C Standards and Cables

Is it a "charge-only" cable that can only do USB2 speeds? How much power can it transport (if there's no id chip in the cable, perhaps this can be deduced by measuring the voltage droop when requesting various power modes over USB-PD)? Can it carry DisplayPort-over-Alternate Mode? -over-Thunderbolt? etc.

Last I checked, 6 months ago, it seemed there was only lab-scale equipment that could do this.

Like I'm traveling with a usbc only monitor connected to a 6800xt and everything has been working fine with it until yesterday.

I updated manjaro packages and the kernel to 5.15, and somehow that resulted in the monitor not working during boot anymore. Which I just don't understand the logistics of AT ALL. How does the host OS relate to video out during boot?

The video out also didn't work once booted into linux but I was able to resolve this by replugging the monitor a couple of times after each restart. Ultimately reverting back to the 5.14 kernel fixed it in Linux but didn't fix it during boot.

So now I just have to enter my LUKS pass blindly and hope for the best or that I never need to adjust my bios settings ever again.

And on a slightly related side tangent how do people who switch to a bluetooth mouse/keyboard adjust their boot/bios? They just don't?

After this, I don't touch third-party USB-C cables unless they charge something I don't care about.

But now I feel a lot better, thanks.

Charging cables are set up in a couple of places in the house, aren't used for data. My dealer for charging cables is Rolling Square. They are nicely built and have complicated adapters on the ends that can handle all the USB-PD stuff, up to 100 Watts:

https://rollingsquare.com

Data-wise, they are just like Apple's charging cables: USB 2, 480 Mbit.

For data, I go with OWC Thunderbolt 4 cables. My two-meter cable should arrive tomorrow.

https://eshop.macsales.com/shop/owc-thunderbolt-4-cables

I feel like there should be a 12-Step program for this.

0 - My double wide qi charger has a USB C socket, but came with a USB A brick and an A to C cable. That works fine, but when I plug it into my kitchen receptacle with built in USB C, it doesn’t work. I ended up moving that to another room for unrelated reasons, so not a big deal either way.

That is not true. The support of Thunderbolt 3 is optional under USB4 spec. Along with a few other nitpick that is not entirely accurate. But it gets the point across

And its time to tell the unpopular story again. ( Because USB-C Supporters hate it )

Trying to help a lawyer out and trying to explain why the $5.00 USB-C cable he'd bought from Amazon wasn't delivering 4K video to his expensive monitor AND powering his laptop too.

Me: OK: so its a USB-C cable, but its not a high data rate USB-C cable.

Him: But, its a USB-C Cable.

Me: but, no, not all USB-C cables are high speed cables. And some of them can't do high speed and power delivery

Him: but... its a USB-C cable: it plugs into the port.

Me: Um... just because it plugs in, doesn't mean its going to work. You can have USB-C cables that are actually slower than the old USB ports.

Him: but.... shouldn't it just work?

And so on. For... 15? more minutes? maybe 30? I finally got him to buy a "proper" belkin USB-C cable .

This basically sums up everything that is wrong with Tech thinking vs User Thinking.

> USB-C cables that support Power Delivery 2.0 and 3.0 can carry a minimum of 7.5 watts (1.5 amps at 5 volts) or 15W (3A at 5V), depending on the device, cable, and purpose.

Nope, all USB C cables are 60W minimum. The connector might support less, but the cables do support 60W minimum.

> USB-C Charge Cable—designed in the early days of USB-C

Nope, nothing wrong with a USB C cable which doesn't have the high speed lanes connected. That's a perfectly specification conformant cable. High speed lanes is the phrase I miss from this too long article.

Here's a much shorter explanation of it all.

A USB C cable always have separate wires for 1) power , either 60W or 100W capable. The latter needs an eMarker IC in the connector 2) a separate pair for 0.48Mbit/s speed USB data (aka USB 2.0) 3) it can have and most do have four high speed lanes (each lane is formed from two wires as differential pairs). These lanes can carry various data , by default it will use two lanes to carry USB data -- at at least 5gbps, if the cable is short enough then 10gbps. (While 20gbps mode over four lanes is defined so few hosts support this we don't need to care.) There are alternative modes besides USB, namely DisplayPort and Thunderbolt. In DisplayPort alternate mode it can use 2 or 4 lanes for DisplayPort. If two then the other two can be used for USB data as above. DisplayPort has its own versions: DisplayPort 1.2 can deliver 8.64 Gbit/s video data over two lanes, while 1.3/1.4 can carry 12.96 Gbit/s and for both double that over four lanes. (DisplayPort 1.4 introduces compression as well which needs to be supported by the monitor and it's very rare to do so.) This is aggregate video bandwidth for PCs: they can drive multiple monitors using a DisplayPort technology called MST. For Mac, you need Thunderbolt.

Thunderbolt. Unlike the previous ones where the cable is functioning the same as a pre-USB C cable and a simple (basically, passive converter) can dole out USB and DisplayPort data this one is a complex bus and both ends needs to have a Thunderbolt controller. The Thunderbolt 3 bus can carry PCI Express and DisplayPort data (USB is provided by the controller presenting a hot plug root hub, due to hot plug nature there's a bevy of problems), the Thunderbolt 4 bus can carry PCI Express and DisplayPort and USB data. (Footnote: Thunderbolt 4 is the same as USB 4 with some optional features made mandatory. It is somewhat unlikely we will see non-TB4 USB 4 controllers so this is mostly just pedantry -- you can treat USB 4 and TB4 as being the same.) The bus bandwidth in one direction depending on cable length can be 20gbps or 40gbps. When allocating this bandwidth, DisplayPort has priority. How much DisplayPort is on the bus in total is a bit confusing due to some history: laptops with one Thunderbolt port most often will only put one DisplayPort 1.2 connection on the bus. Laptops with two ports always have full Thunderbolt and will put two DisplayPort connection on the bus (very rarely, single port laptops will do this too, mostly early workstations). This confusion goes away in Thunderbolt 4, that's always full. But the bus is never faster than 40gbps so even if it is fed by two DP 1.3/1.4 connections, it still can't deliver more than 40gbps data where two independent DisplayPort cables would be able to deliver slightly more than 50gpbs.

Finally, power. If only 5V is required, resistors are used to signal how much power is requested. For 9/15/20V power is negotiated: the devices figure out which one is source and which one is sink, once that's done, the source will communicate how much power it is able to provide. At most 3A can be used normally, at 20V provided the right cable is present, 5A is also a possibility. There is a separate wire for this communication. Using the same communication process, the data roles are decided: one of them will be upstream (think host) one of them will be downstream (think peripheral). There's a sensible default where the upstream data role takes on the source power role but this can be changed using this negotiation.

Footnote: these were fixed power. Today some devices support the PPS (Programmable Power Supplies) feature which allows the sink to rapidly change the wattage as needed. This also requires eMarker cables.

And yes, cables are a mess. https://people.kernel.org/bleung/how-many-kinds-of-usb-c-to-...

Question: does the cable also tell the devices what it is capable of, so that if the devices are capable of 20 V and 5 A but the cable can only handle 5 V and 3 A that is all that the devices will actually do? Or will the devices happily go ahead and do 20 V and 5 A and set your cable on fire?

Anybody has any idea why manufacturer does this?

One example:

http://www.magewell.com/products/usb-capture-hdmi-gen-2

Since then though I got lazy, fell behind in my knowledge, and was comfortable just being able to plug stuff in to charge / transfer data / whatever. It seemed like a solved problem so I went about my work without considering the ins and outs of a simple cable. I mean, it's just USB right? Different connectors, some carry more current, faster speeds over time etc, what more to know?

Then mainly during early Covid when I was often switching between working from home vs in offices, I got sick of how many cables I needed to plug and unplug each morning and when I got home.

I was inspired to solve this problem after one office I worked at had a USB-C dock that magically supported 2 displays, ethernet, etc. So I thought brilliant! I'd get one of those...

Only they don't seem to exist / be in stock anywhere anymore, at least not without a long shipping delay from overseas. So after talking with a sales assistant at the local office supplies warehouse I grabbed something similar (and expensive for what essentially amounts to a fancy USB hub) off the shelf that had video support, and was saddened when it didn't work. That's when I read the instructions that were packaged with the device and apparently it only supported the USB-C with the little lightning bolt icon. Cue hours of reading and research to get up to speed on what all the different little icons I'd never noticed in the injection-moulded plastic meant.

Okay my bad, I should have spent more time keeping up with technology and less time watching netflix.

At least the dock worked for everything else, it wasn't ideal but I could deal with just 2 cables to swap out.

But why then did the dock at the office work?

I grabbed the model number and did some more research and lo and behold it has a built-in graphics adapter. So rather than outputting frames from my still quite capable GTX1070, some cruddy generic display chip was doing all the work through USB and some proprietary display drivers. I tried a couple of games as a benchmark and yep, FPS was woeful. That wouldn't do for my home office at all, so I nixed any hope of getting true video out via USB-C from this device.

All told it was probably less than a day of actual time spent, and a hundred dollars so no big deal for me. But this experience led me to seriously consider that if someone like me with a strong interest and experience in tech gets sent for a spin by something that should be simple and "universal", I don't really understand how the average consumer is supposed to navigate it all. Sure, it's simple once you know, but it is niche knowledge, most people want to learn things about people, their jobs, stuff directly relevant to them and not memorize a grid of cable standards. So I'd wager most people don't read too deeply into it and either a cable/device "works" or is "broken / shit."

Thinking of all the time wasted and frustration people must have swapping devices and cables, the sense that finding a magical combo that works creates a cargo-cult type mindset around brands and devices, as if it's all witchcraft voodoo. I wonder how many perfectly good cables and devices get returned or trashed each day because people think they're "broken."

Anyway old guy has finished yelling at cloud for the day.

All power supplies must tolerate over current by optionally voltage drooping to 5V for 100ms, then (mandatory) tripping a breaker if overcurrent persists. Devices can binary search on the current draw, or not (so long as they actually trip the breaker and don’t just cycle on and off at 10hz).

Plus on inside minus on outside for barrel connector.

Done. Forever. The complete spec could fit on a page.

E.g. a charger + cable combo that works fine with phones and Chromebooks, but plugin a Dell laptop and nothing happens.

Same with older Mac chargers - they'd not do anything when I plug my phone in even if they charged laptops ok (or at least this was the case a few years back)

Where and by whom? In my experience it's always called "type c" for short, dropping the "USB" instead of the "type".