USB-C’s lingering incompatibilities and other complexities, part 1: Direct-connect complications

USB-C will be 22 years old next month, from a published-specification standpoint. Yet it’s still rife with implementation imperfections. Why? Start with the words “published specification”.

One of the many upsides to my now-dual roles as both contributing and associate editor at EDN is deeper-than-prior insight into what topics, and what content pieces focused on those topics, perform particularly well from various website metrics standpoints. This includes my own stuff, of course; I’m not going to share how it does, either in an absolute sense or relative to my colleagues’ contributions, and I’ll also leave you to decide for yourselves whether that silence is driven by humility, embarrassment, or some combination of the two

I begin with this background information by means of introducing one particular piece of EDN content whose enduring stellar performance I will share with you. Week after week, I’m amazed to repeatedly see the article USB Pinout, Wiring and How It Works perpetually parked at the upper stratum of the site traffic spectrum. What’s particularly mind-blowing to me is that the article’s original publication date was January 26, 2010. Clearly, USB is a topic of enduring interest to you, our treasured readership, for oft-obvious reasons!

The latest generation

The date of this article’s initial appearance in EDN is intriguing for another reason; it arrived 4.5 years ahead of the publication of the version 1.0 specification for USB Type‑C, aka USB-C, and therefore doesn’t include mention of this latest generation of the standard. USB-C usage has subsequently become pervasive, courtesy of factors such as its two-fold rotational (and broader two-end) connector symmetry, in combination with higher data bandwidth (extended beyond USB 3.0, introduced in prior USB connector form factors) and higher power (Power Delivery, i.e., USB-PD, building on a proprietary Qualcomm Quick Charge foundation) transfer capabilities.

Yours truly, for example, has crafted three USB-C-focused pieces in recent years (along with innumerable other more minor mentions), the first one focused on the technology, including its generational development history, and the latter two sharing my personal (underwhelming, to be precise) experiences with it:

And speaking of popular writeups, my cohort Bill Schweber followed up my USB-PD piece with his own technology treatise:

USB-C and Power Delivery: Too much of a good thing?

We’re now more than two decades beyond that initial publication date for USB Type‑C Specification 1.0, and I’d love to be able to say that all (or even most) initial implementation warts have been effectively mitigated at this point. I’d love to be able to say that…but I’d be lying if I did. All three of my earlier noted USB-C advancements—connector symmetry, data bandwidth, and power carriage—will unfortunately be demonstrated as enduringly imperfect in the following paragraphs, in fact. Without further ado…

Identity indecision

Let’s start with the fundamentals. Does a particular USB-C cable carry only power? Or power plus data? How much power? And at what peak data transfer rate, if any? Sadly, the answer to these few elementary questions is often consistently unsatisfying, along the lines of “Duh…I dunno. Plug it in, test it and find out for yourself. Then stick an info label on it so you don’t forget.”

Take, for example, this cable:

which came bundled with an inexpensive computer docking station I recently acquired, specifically to test out (and then tear down) its touted DisplayLink capabilities:

By means of association with the specs of its docking station companion, I can make the following cable feature set assumptions:

Power-plus-data support
100W peak power carriage
5 Mbps peak data transfer rate

So, if I only use it with the docking station going forward, I’ll inherently likely know what it can (and can’t) do. But what if the dock dies or the cable more broadly get separated and tossed in a drawer with others? It’s unmarked in its entirety, thereby providing no visual notification of its capabilities (and limitations). This unfortunately quite common anonymity rationalizes the recent unveil of the open-source, albeit MacOS-only (and Apple Silicon-only) from a compiled-code standpoint, WhatCable utility, for example:

And even if I was able to retain the original packaging and documentation associated with the cable, those info supplements might still not suffice. Take this cable, which I’d purchased as part of a six-pack from Woot in March 2022 for $17.97, as illustration of the concept:

The cable itself is again a blank slate, specification-wise. And although in this case the connectors are embossed, they’re still meaningfully information-deficient:

What about the box? It’s of little-to-no assistance, either. The front panel claims that it’s “USB 2.0”, which infers (at least to folks with sufficient technical “chops” to decode the terminology, a scant sliver of the overall consumer community, and still not definitively) that it also supports power-plus-data, albeit the latter only rudimentarily, with a 480 Mbps transfer rate.

And what about power carriage? For that we need to turn to the back panel of the box:

Note the “5V⎓3A” terminology at the top, which translates to a 15W peak power spec. That multiplicative exercise outcome stands in stark contrast to the product page, which states that the cable is 60W-capable (therefore explaining the four-plus-year old scribble from yours truly that you’ll see in the picture). I’ve never encountered a 15W USB-C to USB-C cable, in fact, only 60W ones (along with higher-power variants such as 100W, 140W and 240W), although plenty of 15W USB-A (the current-limiting connector) to USB-C cables alternatively exist.

When I reported the discrepancy to Woot after receiving the initial six-cable (three-box) shipment, customer support told me to keep ‘em and sent me free replacements, whose packaging was labeled in exactly the same (incorrect) way. Eventually, I got a full refund and ended up with 12 gratis, albeit power carriage-dubious, cables for my trouble. In revisiting the product page just now while writing this section, I noticed that Woot eventually appended a correction (albeit, the engineer in me is compelled to point out, using the “=” symbol instead of the correct “⎓”…current and voltage being completely different things, don’cha know):

Please note the Amazon Basics box might state “5V=3A”. This is just a standard industry specification for USB-C cables. HOWEVER, these cables do support charging up to 60W (20V=3A) if paired with a charging brick capable of supporting 60W charging and a device capable of receiving 60W charging.

Beware the upside down

This last case study for today also originated in a several-year-old personal experience. As USB-C approached critical marketplace mass, peripheral equipment (mass storage devices, headsets and other audio equipment, etc.) increasingly shipped by default with integrated USB-C connectors versus USB-A with predecessor gear variants. Sometimes, the manufacturer also bundled a USB-C to USB-A adapter for connection to legacy computers and the like, albeit with tradeoffs such as:

5 Mbps (USB 3.0) peak transfer speeds, and
Negation of USB-PD support that might be minimally beneficial, if not functionally flat-out necessary, since only USB-C includes the necessary communication channel (CC) signals for initial protocol handshaking. Strictly speaking, per the USB-PD specification, modulation on the USB-A-supported Vbus and Vgnd signals could also be used for this purpose, but real-life adoption of this alternative technique is scant-to-nonexistent.

Other times, however, to save a few bill-of-materials cents (not to mention avoiding additional expensive technical support sessions), the peripheral manufacturer would dispense with the backwards-compatible adapter, requiring the customer to as-needed alternatively purchase it standalone. So it was that I picked up a set of two inexpensive ($8.09 total) XAOSUN USB-C female to USB-A male adapters from Amazon, since at the time (and, to a lesser degree, even today), the majority of the computers in my stable met the “legacy” (USB-C-less) criteria:

Good news: they support up-to-10 Mbps peak transfer rates, versus the nominal 5 Mbps speed spec’d for others’ adapters. Bad news: this happens only when the peripheral connector is inserted in one of USB-C’s two possible orientations. In the other (also unmarked) orientation, the adapter will pass through data at only USB 2-compatible 480 Mbps peak speeds:

Please note that this USB-C to USB Adapter only supports single-sided 10Gbps high-speed transmission. The Type-C female port allows you to switch between USB 3.1 speed and USB 2.0 speed with a simple flip of the Type C plug. Now you can enjoy unparalleled transmission quality from your devices!

The manufacturer classifies this explanation under an “Easy to Use” category on the Amazon product page listing. I profoundly disagree. Again, as a “techie” I have awareness from past experience of how 10 Mbps (or even 5 Mbps, for that matter) speeds should be perceived by a user, so if things are proceeding slower than expected, I’ll instinctively realize that I need to:

Cancel the current in-process operation
Disconnect the peripheral
Flip the connector by 180° and re-insert, and
Restart the operation

Conversely, even fundamentally knowing that there’s a problem, far from remembering what’s causing it and how to recover from it, is well beyond the capabilities of the average consumer.

And stepping back, why is this even happening? The answer’s in the “single-sided 10 Gbps” phrasing. As discussed at length in Reddit threads (for example) such as the following:

this limitation is fundamentally driven by cost-reduction moves made by the manufacturer, specifically in passively routing only one set of SuperSpeed differential source pins to the USB-A destination. Routing both sets of source pins, thereby enabling SuperSpeed operation in both possible USB-C orientations, necessitates active circuitry such as Via Labs’ VL160 or a successor or competitor.

Certification vs compliance

Why do situations like the ones described in this writeup, along with those in prior USB-C coverage from me (reminder: listed at the beginning of this piece, as well as the end), occur at all? Isn’t this something that the USB-IF (Implementers Forum) should be dealing with? The answer to this question lies in the differentiation between “compliance” and “certification”. Although USB-IF encourages compliance (via member workshops, testing by independent labs and other means) to “provide reasonable measures of acceptability”, the organization’s specifications are freely published and available for download and implementation by everyone.

Strictly speaking, manufacturers (and products from those companies) are allowed to license and use the USB-IF logo set only if they’ve successfully passed compliance testing. But by now we’ve all likely come across companies that stick the FCC logo on devices and their packaging even though it’s highly unlikely that those products have even applied for FCC certification, far from achieving it (with an omitted FCC certification ID one obvious tip-off). USB logos are presumably also being used in a similarly cavalier manner.

Retailers can also put pressure to bear on suppliers; some require proof of USB-IF compliance determination before they’re willing to stock a particular product (not to mention a broader manufacturer full product suite), for example. And an excessive return rate can also be effective in compelling a retailer to drop a product, not to mention the company that developed it. Still, at the end of the day this fundamentally remains a caveat emptor situation for consumers.

I’ve got one more notable USB-C-related implementation-challenge situation to discuss, but after just passing through 2,000 words, I’m going to save it for next week’s part-two post. Until then, I welcome your thoughts in the comments on anything I’ve so far discussed!

—Brian Dipert is the associate editor, as well as a contributing editor, at EDN.

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