
Raspberry Pi admits to faulty USB-C design on the Pi 4 - close04
https://arstechnica.com/gadgets/2019/07/raspberry-pi-4-uses-incorrect-usb-c-design-wont-work-with-some-chargers/
======
groovybits
From a Pi consumer perspective, this is not that big of a deal.

However, it damages the purpose (in name) of USB C. Isn't C supposed to be the
'all purpose' spec? If we have popular manufacturers failing to follow the
spec, we end up with cables marked as 'compatible with Raspberry Pi' or
'compatible with Nintendo Switch'. To the average consumer (and even most
techies), USB C was supposed to be the 'one size fits all' connector. We're
slowly heading in the opposite direction.

~~~
loeg
This has always been a criticism of USB C and it proves true time and time
again. USB-C tries to be too many things to too many people and ends up with a
huge matrix of incompatibility as a result.

~~~
teilo
And the criticism is completely invalid here. The power spec is very clear and
unambiguous, and there is only one way to get it right. It is not the fault of
the spec when manufacturers cannot be bothered to produce a circuit that has
already been designed for them in the spec itself.

~~~
michaelt
Blame for this problem is 80% on RPi, no doubt, but I'd say 20% of the problem
is someone deciding to allow multiple cables, some with active components in
them.

If they'd instead specified that every detachable USB C cable must be 40 Gbps
/ 100 watt capable, and any lower-spec cable must be captive to the device
(like mouse and keyboard cables are) then this problem wouldn't have happened.

~~~
mmastrac
> If they'd instead specified that every detachable USB C cable must be 40
> Gbps / 100 watt capable, and any lower-spec cable must be captive to the
> device (like mouse and keyboard cables are) then this problem wouldn't have
> happened.

If you are specifying that every cable is going to be $30 minimum, then your
spec is dead from day 0. The USB-C committee has to balance a spec that will
be used by a significant chunk of the planet, not all of whom can afford
expensive cables.

~~~
dingaling
Full-spec cables are only $30+ because that includes a premium margin for
being full-spec, as a differentiator.

If _all_ USB-C detached cables had to meet full-spec then there would be price
competition.

------
thijsvandien
Reminder to self: being an early adopter sucks virtually always.

Edit: Sure, the issue is rather easy to circumvent, but anyone would have
preferred not to have it. At the very least, it affects the resale value. My
point is that whenever the answer to the question 'do I need it absolutely
right away?' is no, it's better to wait a bit, no matter how much you intend
to buy it at some point.

~~~
gambiting
I simply ordered one with the official power supply(at £8 it's cheaper than
literally any branded USB-C charger) and would never even know there was an
issue if not for the articles here.

~~~
mrguyorama
Doesn't this mean that you can't use the Branded power supply with anything
else? I'm so used to all my micro-usb (and hell, even mini and normal USB)
based power delivery systems being 100% compatible, save using a 0.5amp supply
simply won't charge my old phone as quickly as a 1.8 or whatever amp supply.

Is this untrue in the world of USB C? I haven't experienced any oddities yet
with my Pixel 2

~~~
cesarb
The design mistake is on the RPi side, not the power supply side; their
branded power supply should work with anything that needs at most 15W (3A @
5V).

------
jbarberu
While this isn't great, as a consumer I don't really see too big of a problem.
If I get a raspberry pi to use for home automation or as a media center, do I
really need it to work with every USB-C cable? I'd think I'd just find one
that works and let that be the dedicated raspberry 4 cable.

If you're building a product based on Raspberry Pi that you're selling to
others, then sure I could understand the outrage.

~~~
kllrnohj
They chose to use a standard so yes it's a problem that they didn't follow it.
It's pretty cut & dry here.

Fortunately in this case it fails to 0V so it's not a dangerous or damaging
failure, but still the spec literally hands you a schematic. Is it that hard
to just copy it? Why did they even try to be clever and use their own design
in the first place just to save a single 5.1k ohm resistor?

~~~
Sinergy2
I can give the automotive electronics perspective here. Suppose that resistor
costs 2c, including the actual part cost, PCB space, pick-and-place machine
time (inc. more frequent spool replacement). Further suppose you expect to
sell one million of this device.

$0.02 x 1E6 = $20k

If you are the circuit designer making, say, $150k, you just justified about a
month of your salary (after accounting for benefits and other overhead). Your
manager may parade you in front of the team at the next big group meeting as
an example of how to achieve the BOM efficiency the company need to hit profit
margin targets.

~~~
CamperBob2
I've never bought into that reasoning on the automotive side. Selling "one
million of this device," as you say, will bring in $20 billion. So yes, they
can afford $20K to do the job right.

Also, SMT resistors at that quantity level are more like 1/10 of a cent, not 2
cents, and the PnP machine is running anyway. In fact you often end up using
_more_ resistors than strictly necessary, just because the machine holds a
limited number of reels and it's cheaper to use more of the same part to
arrive at a desired value than to add a new line item.

Things should be as cheap as possible, but no cheaper. Optimizing the cost of
individual resistors is almost always a classic example of measuring the wrong
thing. We should strive to avoid making excuses for doing that.

------
Havoc
>a board revision with a spec-compliant charging port should be out sometime
in the "next few months."

wohoo. Glad I waited. Hoping they make some incremental gains on the heat
situation too

~~~
Luyt
Normal-sized HDMI connectors would be great, too.

------
soared
Interesting that two major-ish companies sell products that are out of spec
(rpi and Nintendo). Is there any insight on why these decisions were made?
Business and engineering opinions would be equally interesting.

~~~
topspin
Well, I followed through to Benson Leung's post where he cites and transcribes
the actual USB-C specification and I'm not surprised that the spec is
occasionally ignored. The supposedly 'normative' circuit diagram deviates from
a conventional circuit diagram. If you want an engineer to pay attention to
your instruction don't invent some ad-hoc diagram technique; be concrete and
prescriptive, and assume you're dealing with a low caliber worker, because 99%
of the time that's exactly who will get tasked to deal with your
specification.

[1] [https://medium.com/@leung.benson/how-to-design-a-proper-
usb-...](https://medium.com/@leung.benson/how-to-design-a-proper-usb-c-power-
sink-hint-not-the-way-raspberry-pi-4-did-it-f470d7a5910)

~~~
qtplatypus
How does it diverge from a conventional circuit diagram?

~~~
topspin
See the circuit diagram above labeled "Excerpt from the reduced Pi4 Model B
schematics..." that appears above the spec diagram? That is what I mean by a
"conventional" diagram. That is the sort of diagram that people tasked with
engineering boards (as opposed to writing standards) are use to dealing with
all day. The spec diagram looks like an abstract block diagram, as opposed to
a concrete circuit.

Now, you are very likely to say something like "but the spec diagram is a
correct circuit diagram and the engineer should be expected to comprehend and
correctly implement a circuit using it." And you're not wrong. But
unfortunately, as is clearly evident by the frequency of failure to convey the
intent of the spec, this expectation is too great. It shouldn't be but it is.
That's a difficult thing to accept. For many it is simply impossible to
accept. But yet that's the cold, simple truth and standing on ceremony doesn't
change it.

When it costs money, in the form of lost sales due to disappointed customers
or excessive support costs, "better" (as in more concrete, prescriptive)
circuit diagrams are provided. One can see this in the datasheets and
application notes from successful component manufacturers. They do this
because they have to take the calls when engineers misunderstand things or
need their hand held. They do this because they hear from managers and
executives when their products are not "easy" to integrate.

Standards authors don't feel this pressure, so the subtle and easily dismissed
gap between what appears in standards documents and what people actually want
(and therefore pay attention to) is wider. What is wanted is something that
appears nearly indistinguishable from what the engineer would expect to see
while using Altium or Eagle or KiCad or some other commonly used EDA tool, and
not a specification sufficient generalization.

------
vardump
I have two RPi4B 4GB models. They work perfectly with the very cheap
PSU/charger ($8) from the Raspberry Pi Foundation. $8 is less than a cost of a
USB-C cable.

If you want to complain something about the product, I think unfinished
software would deserve more attention. The current desktop performance doesn't
reflect the capabilities of the system. I guess it'll significantly improve
once OpenGL ES 3.2 (and hopefully Vulkan!) drivers will be complete.

Other minor issue I had was RPi4B not recognizing the HDMI display. I had to
manually force it and this caused loss of HDMI audio. Using the official
Raspberry Pi branded micro-HDMI cable.

I hope Raspbian will eventually have a 64-bit version. Out-of-order cores can
benefit from more registers in 64-bit mode. More registers allows the compiler
to reduce true and false dependencies, leading to faster code execution.

CPU wise it's nice, quad Cortex A72 is a _huge_ boost compared to A53.
Hardware accelerated omxplayer can play 4K HEVC content nicely. USB 3 ports
have up to 4 Gbit/s bandwidth, and it's not shared with the now truly full
speed gigabit ethernet.

I'm very happy with the product. RPi4B is a _very_ capable system for its
price. And it'll just get better over time.

~~~
Luyt
There is a 64-bit Kali Linux image for the Raspberry Pi.

[https://www.offensive-security.com/kali-linux-arm-
images/](https://www.offensive-security.com/kali-linux-arm-images/)

------
tracker1
I mentioned in an earlier thread, I had so much trouble using any charger I
already had with the 3B+, I just assumed it wouldn't work with most chargers
this time either and ordered a kit with an official one.

~~~
ageofwant
Same, I traced it back to my penchant for buying cheap shit cables. Measure
the voltage at the back of the USB connector on the Pi3, it should be > 4.9
always.

------
seiferteric
Is it possible to fix? Sounds like it's just missing a resistor? Break out the
soldering iron and maybe could it could be salvaged.

~~~
HeWhoLurksLate
Part of the problem with this seems to be that the extra pads are not exposed,
making it _really_ hard to do fix without removing the connector.

------
chadlavi
I preordered, and it hasn't shipped yet. I wish there were an option to wait
and get a fixed one later instead.

~~~
heywire
I ended up cancelling my pre-order from Element 14, you could potentially do
the same depending on who you ordered from. I didn't cancel because of this,
but just because I got really busy with work and I know it'll be a few months
before I get to pull it out of the drawer. Better to let someone else have it
to use than take a pre-order spot for my desk drawer.

------
w0mbat
I think the Pi team unintentionally became dependant on the time window they
normally spent using test boards based on pre-release versions of the Broadcom
sytem-on-a-chip. When the Broadcom chip went final really early they ended up
shipping a half-baked version of the board along with it.

------
agumonkey
They should offer group labs to DIY fix the pcb

------
Bob995
Do I still need to pay them extra cash to get video codecs codes?

------
jakeogh
"E-marked cables are fully featured USB-C cables with chips inside"

That's um... awful.

~~~
jhbhjjhvhjkgh
The whole USB-C PD spec is overly complicated but in this case these chips are
to ensure that someone doesn't push 4a/19v over an improperly built USB-C
cable - that can lead to fire and burns.

Also, other cables may have chips in them for data negotiation, specifically
TB3/PCI encapsulation (the data rate is so high that over 6 inches you start
to run into issues).

~~~
jakeogh
So, the spec allows an under-gauged cable to be plugged into a power outlet,
and then relies on software (instead of a fuse) to not start a fire.

I'm looking for a word... worse than awful...

~~~
wlesieutre
You can plug a 5 amp rated extension cord into a residential plug on a 15A
breaker and the breaker won’t protect you from overloading the cable with 15A.
So yes, those sorts of light duty cables have their own fuse to prevent this.

But I _really_ would not trust all the no-name vendors flooding the market
with shitty USB cables to include correct safety measures in all of their
cables, so requiring cables to specifically request higher power levels seems
like a better precaution to rely on in this case.

------
kawsper
>a board revision with a spec-compliant charging port should be out sometime
in the "next few months."

Are they going to change the boxes and their product spec to remove USB-C from
it when they are not USB-C compliant?

------
rolltiide
Great maybe theyll deliver the 8gb model while theyre at it

~~~
ars
There is no 8gb model, there is no memory chip of that type that would fit in
the spot.

~~~
rolltiide
hm alright, thank you

------
fit2rule
Damn, did they just Osborne themselves? I for sure have decided to hold off on
a Pi-4 until this issue is fixed, since its really a hassle.

Maybe a smarter move would've been to bundle the Pi-4 charge (non E-cable) to
avoid dissatisfaction with this mis-design ..

~~~
baq
They provide their own charger. It works, I’ve got one.

~~~
tjohns
Yes, but it's an extra expense. If you've got spare USB-C chargers you could
use, it's tempting to wait.

~~~
dividuum
Their USB charger costs 7€. From my experience: Just buy their charger and
you'll have no problem. I've seen so many attempts at powering the Pi with
alternative sources that suck and cause problems. 7€ is worth avoiding that.

~~~
TheRealPomax
Remember when the EU had to pass laws to prevent everyone from making their
own bloody chargers with proprietary plugs for mobile phones, because _no one
needs their own custom charger_? Yeah, that.

It doesn't matter how cheap their charger is, no one should need to even buy
one. RasPi botched their USB-C implementation, and the solution to that is not
"buy yet another charger", it should be "we're fixing the design immediately,
and it's going to cost us a fair bit but you can send your board back to get
it replaced"

~~~
dividuum
That's actually a good point I didn't consider.

------
solarkraft
How hard is it to to copy a [expletive] schematic?

Edit: I'm serious. What convinced them to implement a design different from
the example in the spec that simply _does not work_ (hello, testing?)?

~~~
SSilver2k2
The USB-C spec is 300 pages with multiple errata and revisions. It's not just
one schematic.

~~~
openthc
FTA: Benson Leung seems to think they should have copied figured 4-9 --
[https://medium.com/@leung.benson/how-to-design-a-proper-
usb-...](https://medium.com/@leung.benson/how-to-design-a-proper-usb-c-power-
sink-hint-not-the-way-raspberry-pi-4-did-it-f470d7a5910)

I don't think a long and imperfect specification is a good excuse for getting
this one wrong -- since this specific part of the spec is a MUST and accurate.

