5 ms·

Did I get this right? some cables have an MCU that gets power through a 1K series resistor on CC2? That MCU also sources ground through the cables GND?

fhars 1y ago
USB3 cables are black magic, anyway.
- lxgr 1y ago
  Contrary to many other electronics standards, the USB-C spec is just a free download away.
bloggie 1y ago
Yes and this is a requirement for many different connection modes. https://en.wikipedia.org/wiki/USB-C#E-Mark https://en.wikipedia.org/wiki/USB-C#E-Mark
alvarop 1y ago
The 1k resistor just lets the device know there’s an MCU on that line. The device would then provide power on that pin before talking to it
jmux 1y ago
The USB-C step is humongous, and hard to implement. the complexity is high, but how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? users aren’t going to be able to tell the difference (using a cable with no data lines is already a super common issue with people getting into MCUs) so the device needs to be able to tell how much data and power the connected cable can distribute automatically. this also why usb-c extension cables (M-F) aren’t spec complaint it’s a real cool port, but the complexity demon is definitely present in the spec :)
- userbinator 1y ago
  but how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? By attempting to link up at the highest supported speed and downshifting if there's no valid signal? Ethernet had this figured out decades ago.
  - lxgr 1y ago
    USB-C doesn’t only carry USB data. I’m not sure if e.g. Displayport even has the capacity for link training (and there are USB-C to Displayport cables that have to support legacy devices that know nothing about USB); HDMI (until 2.2 or so) definitely does not. It’s ok to not agree with the USB-IF’s tradeoffs in their solutions, but denying the complexity of the problem space can be a hint that you don’t sufficiently understand it to pass that kind of judgement.
    - jauntywundrkind 1y ago
      Intel has a flow for how link training is done on DisplayPort. Probably shouldn't be surprised but it involves communicating over the AUX channels. Is this something that a sizable % of computers can do? For some reason I thought aux channel was semi free for use, that it could be for Ethernet or USB in a pretty naked form. Didn't realize that needed mode switching? https://www.intel.com/content/www/us/en/docs/programmable/683273/22-2-20-0-1/displayport-link-training-flow.html https://www.intel.com/content/www/us/en/docs/programmable/68...
      - lxgr 1y ago
        Ah, so maybe DisplayPort has mandatory link training then, which would indeed allow unmarked cables. But to GPs point, there still needs to be a way to tell the source that a given cable is a USB-C-to-DisplayPort one in the first place. So why not include the metadata on what signal grades it’s rated for in that same indicator? That’s exactly what e-markers are.
    - userbinator 1y ago

fhars 1y ago

USB3 cables are black magic, anyway.

lxgr 1y ago
Contrary to many other electronics standards, the USB-C spec is just a free download away.

bloggie 1y ago

Yes and this is a requirement for many different connection modes. https://en.wikipedia.org/wiki/USB-C#E-Mark https://en.wikipedia.org/wiki/USB-C#E-Mark

alvarop 1y ago

The 1k resistor just lets the device know there’s an MCU on that line. The device would then provide power on that pin before talking to it

jmux 1y ago

The USB-C step is humongous, and hard to implement. the complexity is high, but how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? users aren’t going to be able to tell the difference (using a cable with no data lines is already a super common issue with people getting into MCUs) so the device needs to be able to tell how much data and power the connected cable can distribute automatically. this also why usb-c extension cables (M-F) aren’t spec complaint it’s a real cool port, but the complexity demon is definitely present in the spec :)

userbinator 1y ago
but how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? By attempting to link up at the highest supported speed and downshifting if there's no valid signal? Ethernet had this figured out decades ago.
- lxgr 1y ago
  USB-C doesn’t only carry USB data. I’m not sure if e.g. Displayport even has the capacity for link training (and there are USB-C to Displayport cables that have to support legacy devices that know nothing about USB); HDMI (until 2.2 or so) definitely does not. It’s ok to not agree with the USB-IF’s tradeoffs in their solutions, but denying the complexity of the problem space can be a hint that you don’t sufficiently understand it to pass that kind of judgement.
  - jauntywundrkind 1y ago
    Intel has a flow for how link training is done on DisplayPort. Probably shouldn't be surprised but it involves communicating over the AUX channels. Is this something that a sizable % of computers can do? For some reason I thought aux channel was semi free for use, that it could be for Ethernet or USB in a pretty naked form. Didn't realize that needed mode switching? https://www.intel.com/content/www/us/en/docs/programmable/683273/22-2-20-0-1/displayport-link-training-flow.html https://www.intel.com/content/www/us/en/docs/programmable/68...
    - lxgr 1y ago
      Ah, so maybe DisplayPort has mandatory link training then, which would indeed allow unmarked cables. But to GPs point, there still needs to be a way to tell the source that a given cable is a USB-C-to-DisplayPort one in the first place. So why not include the metadata on what signal grades it’s rated for in that same indicator? That’s exactly what e-markers are.
  - userbinator 1y ago