Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

USB Cheat Sheet

fabiensanglard.net

Post reply on HN
Print view View original

81–90 of 174 posts

Re: USB Cheat Sheet

#81

Post by colejohnson66 »

rob74 wrote: post #37
microtonal wrote: post #33

Earlier quoted context omitted.

Can be USB 3 [...] USB 2, so it is a bit hard to tell. ...or Thunderbolt, USB 4, DisplayPort (through Alt-mode or encapsulated in Thunderbolt), or HDMI (Alt-mode), or MHL (Alt-mode), USB Power Delivery... Unfortunately, not every cable with USB-C connectors can carry all of these. E.g. there are USB-C cables that can only carry USB 2. Or cables that can carry USB 3, but not Thunderbolt. Also, not all cables can carry…

Of course USB-C makes this worse, but the problem already started earlier: a few years ago I connected my phone to my computer with a USB-A to micro USB cable and was scratching my head why it didn't work. Then I remembered that the cable had come with some Bluetooth headphones and was only a charging cable without data lines...

Desktop speakers do this still. Instead of simply being a USB speaker set, they use the line out jack for audio and a USB plug for power.

Re: USB Cheat Sheet

#82

Post by jbverschoor »

jsjohnst wrote: post #46
411111111111111 wrote: post #45

Earlier quoted context omitted.

There was a really short timeframe when I was really positive about USB, but that has been long lost since. They should've never allowed cables to only provide some capabilities and still get the branding. Having capabilities for connectors was fine imo, but also accepting them with cables was bad because you cannot really find out what it supports and where the issue originates of something goes wrong

It’s why I always buy TB3 (or now TB4) cables rather than a cheaper USB-C to USB-C. Due to the strict requirements on TB cables, you can pretty much guarantee it’ll support any use case (alt modes, PD, etc). Sometimes overspending is worth the headache prevention.

Apple just released a €159 cable

Re: USB Cheat Sheet

#83

Post by asciii »

jbverschoor wrote: post #77
adrian_b wrote: post #65

Earlier quoted context omitted.

No, some of your rates are wrong. The so-called 5 Gb/s USB has a data rate of 4 Gb/s. The marketing data rates for Ethernet are true, i.e. 1 Gb/s Ethernet has a 1 Gb/s data rate, but a 1.25 Gb/s encoded bit rate over the cable. The marketing data rates for the first 2 generations of PCIe, for all 3 generations of SATA, and for USB 3.0 a.k.a. "Gen 1" of later standards, are false, being advertised as larger with 25% (…

Is that the same intel that “forgot” to mention that they overclocked a demo cpu and used ndustrial water chiller?

I was curious and went looking for it. That's pretty hilarious oversight!

https://www.tomshardware.com/news/intel-28-core-cpu-5ghz,372...

Re: USB Cheat Sheet

#84

Post by kevin_thibedeau »

IvanK_net wrote: post #74

Fun fact: USB 2.0 webcams have been existing for over 10 years. USB 2.0 is 60 MB/s. A pixel of an image is 3 Bytes. A 1920x1080 FullHD image is 6.2 MB. At 30 frames per second, second of a FullHD video is 186 MB. How did they do that? Answer: frames are transferred as JPEG files. Even a cheap $15 webcam is a tiny computer (with a CPU, RAM, etc), which runs a JPEG encoder program.

The cheap ones are using hardware JPEG encoders. The associated micro isn't powerful enough to do it in firmware alone.

Re: USB Cheat Sheet

#85

Post by kevin_thibedeau »

hyperman1 wrote: post #21
dschuetz wrote: post #19

So where exactly does USB-C fall into? I have 2 different generations of USB-C hosts, and they behave quite differently when approaching max cap, especially with high-quality low-latency audio (USB-C was supposed to be de-facto replacement for FireWire).

It's orthogonal. Usb A is a host side connection Usb B (normal/mini/micro) is a client side connector Usb C is a 2 way connector. Each of them can be implemented for each USB version, except USB C came later and makes no sense befor USB 3. Then USB versions added features, signalling conventions and wires. But the USB A and B connector are backward compatible all the way to USB 1.0 1.5Mbit/s

On-the-Go allows mini and micro B to be host as well.

Re: USB Cheat Sheet

#86

Post by masklinn »

kevin_thibedeau wrote: post #84
IvanK_net wrote: post #74

Fun fact: USB 2.0 webcams have been existing for over 10 years. USB 2.0 is 60 MB/s. A pixel of an image is 3 Bytes. A 1920x1080 FullHD image is 6.2 MB. At 30 frames per second, second of a FullHD video is 186 MB. How did they do that? Answer: frames are transferred as JPEG files. Even a cheap $15 webcam is a tiny computer (with a CPU, RAM, etc), which runs a JPEG encoder program.

The cheap ones are using hardware JPEG encoders. The associated micro isn't powerful enough to do it in firmware alone.

Surprised they don't use a hardware video encoder, is it because the well and efficiently supported formats are all MPEG, and thus have fairly high licensing cost on top of the hardware? Or because even efficient HVEs use more resources than webcams can afford? Or because inter-frame coding requires more storage, which (again) means higher costs, which (again) eats into the margin, which cheap webcam manufacturers consider not worth the investment?

Re: USB Cheat Sheet

#87

Post by grishka »

IvanK_net wrote: post #74

Fun fact: USB 2.0 webcams have been existing for over 10 years. USB 2.0 is 60 MB/s. A pixel of an image is 3 Bytes. A 1920x1080 FullHD image is 6.2 MB. At 30 frames per second, second of a FullHD video is 186 MB. How did they do that? Answer: frames are transferred as JPEG files. Even a cheap $15 webcam is a tiny computer (with a CPU, RAM, etc), which runs a JPEG encoder program.

Hm. But then wouldn't it make more sense to just stream the raw sensor data, which is 1 byte per pixel (or up to 12 bits if you want to get fancy), and then demosaic it on the host? Full HD at 30 fps would be 59.33 MB/s, barely but still fitting into that limit.

But then also I think some webcams use H264? I remember reading that somewhere.

Re: USB Cheat Sheet

#88

Post by kevin_thibedeau »

formerly_proven wrote: post #39
eugene3306 wrote: post #15

just curious. Can USB3 work without D+ and D- ?

USB 3 and previous standards are completely separate connections and software stacks - the USB 1/2 D+/D- pair does not interact at all with SSRX/SSTX. You should be able to literally cut the D+/D- wires in an USB 3 cable and it should still work as a USB 3 cable.

I doubt any normal hosts will enumerate a USB device without the USB 2 data lines. PD will definitely not work. You might be able to get an alt mode running.

Re: USB Cheat Sheet

#89

Post by Fatnino »

kashunstva wrote: post #3

> May 05, 2025 The article is dated May 5, 2025. I've long been wondering about the future of USB.

It's a form of SEO. Google promotes "fresh" content, so if it sees a date less than a year ago it often assumes the content is better. Normally you will see this abused by crappy content mills using a plugin that constantly updates the date on their garbage.

Putting a static date from 3 years in the future seems like a quick a dirty hack to do the same thing.

Post reply on HN