Had the same problem with Raspi 4B.
Problem was dependent on screen resolution (!!).
With 1920x1080, wlan0 became disconnected after it was
ok at lower screen resolutions. Was in 2.4GHz band.
After turning on 5GHz in the router and going into
the network preferences (right click the network icon top
right on screen) and SSID ... and checking "automatically
configure options" the connection remains stable (so far :D ).
Had the same problem with Raspi 4B. Problem was dependent on screen resolution (!!). With 1920x1080, wlan0 became disconnected after it was ok at lower screen resolutions. Was in 2.4GHz band. After turning on 5GHz in the router and going into the network preferences (right click the network icon top right on screen) and SSID ... and checking "automatically configure options" the connection remains stable (so far :D ).
When I connect my USB 3 hub to it, I lose my WiFi :(
I Googled it when it happened a while back, and apparently other people have this problem with the MacBook Air too.
Some choose to shield the USB 3 cable with tinfoil. Personally I opted to connect a USB 3 Ethernet interface to the hub and use wired Ethernet when I use the hub.
We got to know about the design change when a rather large and sprawling local leisure centre reported that often when someone used their walkie talkie near a PC, the screen filled with random characters and sometimes the dot matrix printers would 'go haywire' (CTRL-P = Print what's displayed on the screen).
In effect, the rf signal from the walkie talkies was 'mashing the keys'.
The immediate fix was to swap in some older keyboards, the longer fix was down to Olivetti using better shielding and some appropriately-placed capacitor decoupling on the power and signal lines.
Havnm't heard that brand in a while! I now remember I still have an 486 DX4 100MHz Olivetti laptop. Which is kind of pink-red-brownish.
wrapping 3rd party adapter in tin foil actually show much better speedtest results when connected, then without the foil.
I once heard something about that frequency working better with water molecules, but after looking it up I think it's a myth.
Don't use a cheap cable, use one rated for 4k, and see if that helps.
This makes me think of the bug that the QCA AR9331 SoC has. The AR9331 is extremely common in small travel routers, but it has a fun bug where one of it's clock sources is shared between the 802.11 wifi and the USB port. IF the USB port is negotiated at USB 1.x speeds AND the 802.11 radio is scanning, the USB will freak out and die. This generally requires the 802.11 radio to be in client mode rather than AP mode. You can read some details about this on the old OpenWRT forum, if it survived the great forum purge of 2018.
Wifi shows as 'connected' but reality is only fraction of packets go through because of interference problems
some online reference from intel on usb.org:
> the noise from USB 3.0 data spectrum can be high (in the 2.4–2.5 GHz range). This noise can radiate from the USB 3.0 connector on a PC platform, the USB 3.0 connector on the peripheral device or the USB 3.0 cable. If the antenna of a wireless device operating in this band is placed close to any of the above USB 3.0 radiation channels, it can pick up the broadband noise. The broadband noise emitted from a USB 3.0 device can affect the SNR and limit the sensitivity of any wireless receiver whose antenna is physically located close to the USB 3.0 device. This may result in a drop in throughput on the wireless link.
The money quote:
> With the HDD connected, the noise floor in the 2.4 GHz band is raised by nearly 20 dB. This could impact wireless device sensitivity significantly.
Besides having properly shielded devices and cables (which manufacturers often don't bother doing), they also recommend that the plug in the laptop be fully shielded or enclosed in a metal chassis (which is fulfilled by having an entirely metal case).
I don't know of a cheap RF analyzer but I'd like to get one at some point. I'm curious how many common devices actually adhere to the FCC regulations and/or standards like USB 3, compared to how many are just cheaply made.
A SDR might work, and they're quite versatile. Unfortunately, the cheap RTL-SDR ones don't get to 2.4 GHz without a downconverter.
That’s one of the features I love about my Aruba APs/controller. Not only does the APs dedicated as AirMonitors/SpectrumMonitors monitor at both the Wi-Fi level and radio spectrum level and shift frequencies as needed, but I can also get a high quality live visualization of radio spectrum interference. Definitely not cheap though!
FAE = Functional Accessibility Evaluator
I bet that's it.
2560x1440 @ 60 Hz with CVT-RB timings has a pixel clock of 241.5 MHz. The TMDS bit rate is 10x the pixel clock, and 2415 MHz is right in the lower end of the 802.11 band.
If the Pi can be convinced to use CVT blanking, that'll raise the pixel clock to 312 MHz, which should be fine.
Now the question is who screwed up. Is it a leaky cable? Is it bad PCB design? Is it a problem internal to the SoC? Is it a power delivery issue? Knowing the RPi foundation and Broadcom, I bet one of them screwed this up for all RPis and it isn't just a bad cable.
Not an electrical engineer: which measures are usually adapted to handle termination issues?
Forcing a different pixel clock is probably the easiest fix, and since the ports claim to do 4kp60, that should be possible (if the display supports it).
Changing the refresh rate would work too, but some monitors can be pretty picky about that.
The interference can be internal interference in the device, or interference from other wireless devices. In many cases, the problem are even devices that shouldn't emit RF at all, like power supplies, switches, light bulbs...
Another common issue is poor antenna design (eg. attenuation when you hold the device, or strong directionality of an antenna that should not be directional).
And, last but not least, physical obstacles. Most people understand that concrete walls with rebar will block signal, but a surprisingly large number of people try to use aluminum stands or cases for devices with wireless radios.
All those factors will cause connection issues, and they are really common because debugging them is so hard (who has a spectrum analyzer at home? How do you find out which one of dozens of electronic devices is emitting RF that it shouldn't?)
The VideoCore (Broadcoms GPU) is the main processor on the thing, and the cluster of ARM cores that run Linux are more of a coprocessor which can only see some of RAM.
> 5GHz WiFi has more bandwidth than 2.4GHz, so typically will involve larger IO buffers in the driver, which could easily be enough to expose a memory scribbler
He's saying 5 GHz will expose the scribbler, and the opposite is happening, only 2.4 GHz fails.
Although, if my theory that the IO buffers are different sizes is true, then that could perturb memory layout enough to expose/hide the bug in either direction.
I do agree that the different IO buffers might hide the bug in one instance, but I think this is just plain old RF noise.
I need more sleep.
As an embedded engineer, it was a hard lesson for me to learn that not all issues are software issues and the hardware may need to be investigated.
This is especially true where there is different behaviour between units. You can't just assume that your 99% estimation (plucked out of thin air) is correct and discredit other potential explanations.
Then, after you done ruling out the most likely and easiest explanation to test, you can then start exploring the remaining possibilities. Skipping to the more exotic explanations sounds more interesting but it's poor use of time if there's still low-hanging fruit out there.
Unless USB is involved, then it's something in the USB stack...
These kinds of problems are common in embedded computers, like the Pi. Just as common as software.
E.g. the Xilinx ZynqMP includes the same Cortex-A53 complex the Raspberry Pi 3 has. They also included CCI-400 coherent interconnect switch to it, and also included the SMMU-500 IOMMU that partially interfaces with the A53 interconnect, but is effectively independently programmed and also controls access to DDR3/4 from the SATA, Displayport and PCIe controllers.
Per the original topic, have they released a full datasheet/reference manual for the Pi 4 SoC yet? I’ve yet to see one other than a VERY high-level overview of it’s new pieces.
Ha. It's Broadcom... They're never going to release one.
And all that costs extra developer time -and money.
I think the other operating systems available for the Pi are roughly in the same boat (Windows & RiscOS). There was a nascent Minix port at some point, I wonder if it was abandoned.
(for avoidance of doubt, I wrote that blog post)
I was just explaining what the OP was asking for. I personally believe it's a EMI-related hardware issue.
Try to reproduce with a different OS/kernel.
Actual measurement that a Pi with HDMI at the affected reoslutions radiates over the bottom end of the wifi band.
> Why does my Thunderbolt 3 device not work with Dell's XPS laptops?
Some users on the Dell forum have found that reducing the power output of the WiFi network adapter to 75% fixes the problem.
When a current flows through a p&n junction, photons are emitted (and an LED is just a diode that happens to emit photons at the wavelengths of visible light). And it works in both ways, if you hit a p&n junction with photons, you produce a current, not only LEDs - any diode will do that, they're all potential photodiodes, it's just that some are more sensitive than others.
You can cause a lot of chips to reset if you shine a bright beam of light to its exposed die, a common way to test chips.
It's also one reason (in addition to cost) that most diodes are sealed in plastic package, not glass package. Fun experiment: buy some 1N4148 small-signal diodes in glass package, connect it to a Darlington-pair transistor amplifier, and shoot the flashlight, you'll see some funny thing on the oscilloscope.
Putting a light-sensitive chip (I think it was a wafer-scale package with no casing) on a board that's intended for use outside of an enclosure was a really big oversight.
Popular buzzword (Raspberry Pi), surprising unexpected outcome (most consumer electronics people are familiar with don’t react to light), manufactured outrage/schadenfreude (look how they screwed this up!)
Good analysis. In both cases, I see the popular press reports them in personified language, "Xenon Death Flash, or Why the Raspberry Pi 2 is Camera Shy", and "Why the new iPhone is Allergic to Helium". If we replace "Raspberry Pi 2" with "semiconductor p&n junctions", and replace "new iPhone" with "MEMS oscillators", it probably won't be news anymore.
> manufactured outrage/schadenfreude
An interesting case as well. I see both incidents as undesirable side-effects that better to be prevented, but I don't think they are major design flaws.
So sure, that version would get no notice.
You were missing a router swap on your list.
While it might seem a bit overkill try restarting your router’s WiFi to see if it magically works. I had a war with a pi zero W not that long ago...turns out the 2 band wireless would just die sometimes. Turned out to be an issue with the router ️
The plane can't take off because the carpet is the wrong kind of orange.
I once had a keyboard that wouldn't work when the monitor was outputting at 75hz. Had to be 60hz or else nothing. The joys of wireless keyboards.
I can't get it to fail now, but it is not connected to a monitor anymore.
Don't let the AI-heavy marketing distract. It's an Ubuntu PC effectively.
Can you elaborate what you're doing that is slow? In my experience, CPU wise it's plenty fast, matching typical desktop from 2008. Although memory bandwidth could be better...
> Had the same problem with Raspi 4B. Problem was dependent on screen resolution (!!). With 1920x1080, wlan0 became disconnected after it was ok at lower screen resolutions. Was in 2.4GHz band. After turning on 5GHz in the router and going into the network preferences (right click the network icon top right on screen) and SSID ... and checking "automatically configure options" the connection remains stable (so far :D ).
Most people on HN do this. It doesn't format the quote in any way, but it works.
I wish the RPi was this standalone microserver that had its own flash memory (SD cards are known to fail) that you could plug into your home network and act as a personal server.
Maybe one day it will be possible to do some basic GSM data with a RPi.
The philosophy of the RPi is that they won't really add features to it unless a bulk of the user base would use the feature. For example they were hesitant to even build the WiFi into it because users who wanted that could always get a USB chipset, and building it in adds BOM cost.
Because with GSM you'd also need a plan for it, I don't really predict they'd add that. Especially since you can get it in hat format already.
Also doing a quick survey for the rated cycle counts on M.2 vs SD card slots:
M.2: I found this one  which is $0.768 for only 60 cycles
SD: This one  is $0.6256 for 5,000 cycles
I'm not sure why you'd say M.2 is more reliable, considering users often cycle storage dozens if not hundreds of times.