4 ms·

That's how it's supposed to work, yeah. But there is some trash out there in the world. A lot of it, actually. Some naughty cables work with some naughty char

That's how it's supposed to work, yeah. But there is some trash out there in the world. A lot of it, actually. Some naughty cables work with some naughty chargers work with some naughty devices. Postel's Law in action, I guess? Usually the best place to fix it is by getting rid of the bad cables. Usually.

mschuster91 4mo ago
> Usually the best place to fix it is by getting rid of the bad cables. Usually. No. There is no USB-C to C cable that will charge a badly implemented device with a standards compliant charger. That is the entire point. An USB A to C cable is completely standards-compliant and safe, even if it always supplies 5V on the C end - any standards compliant USB-C device should not activate the MOSFET on its Vbus line unless it successfully negotiates via CC.
- seba_dos1 4mo ago
  They mean bad USB-A to C cables with no resistor on CC line. Of course this is broken junk which will work with some devices and won't with others. I've also seen cables with resistors on both CC lines, which is also broken but in a slightly subtler way.
  - exmadscientist 4mo ago
    Right. That phrase "standards-compliant" in the above comments is doing a lot of heavy lifting. A lot of devices are not actually standards-compliant. Some are close. (This may actually be worse.) My experience has been that if the source and sink are broken, they are often hilariously badly broken and it is pretty easy to figure out that they are the problem, if not quite exactly what they've done wrong. But if things are flaky and weird and don't really make sense, it's probably the cable. Try a known-really-seriously-actually-standards-compliantly-good cable and many problems go away, even if the source and sink aren't perfect. (Many sources and sinks aren't standards-compliant because, even though they easily could be, they're trying to work around the other end not being standards-compliant itself, because that's what you've got to do to sell a product. So they're close but not quite there. This is not always ideal.)
  - stephen_g 4mo ago
    But it’s not what anyone was talking about. Such a cable should be really quite rare because it’s unlikely to work at all in most situations, whereas devices with USB-C ports that don’t work with PD chargers (due to a cent’s worth of missing Rd resistors) are irritatingly common, because they do work with USB-C to A cables!
    - seba_dos1 4mo ago
      Huh? It seems clear to me that this is what exmadscientist was talking about, any other interpretation just doesn't make sense. And no, such cables would still work in plenty of cases. You usually get them by having them bundled with devices they do work well with. In fact, they always work fine with the kind of devices you mention. These cables aren't as common as USB-C-shaped junk that's missing resistors on the receptacle, but I stumbled upon them anyway and I didn't really try to.
- megous 4mo ago
  You may wish to re-read the type-c specification, especially 4.5.2.2.3.2: "A USB 2.0 only Sink that doesn’t support accessories and is self-powered or requires only default power and does not support USB PD may transition directly to Attached.SNK when V BUS is detected." or 4.5.2.2.5: "A port that entered this state directly from Unattached.SNK due to detecting V BUS shall not determine orientation or availability of higher than Default USB Power and shall not use USB PD." or 4.5.2.2.11.2: "The port shall transition to Attached.SNK after tCCDebounce if or when V BUS is detected." CC detection, let alone PD negotiation is not needed. You can draw up to 2.5W right away from Vbus and be standard compliant without wiring anything to CC signals. Of course if you try this with a DRP device like a smartphone, you'll get no power. But that's not really an issue for type-c chargers or USB A-C cable assemblies.

mschuster91 4mo ago

> Usually the best place to fix it is by getting rid of the bad cables. Usually. No. There is no USB-C to C cable that will charge a badly implemented device with a standards compliant charger. That is the entire point. An USB A to C cable is completely standards-compliant and safe, even if it always supplies 5V on the C end - any standards compliant USB-C device should not activate the MOSFET on its Vbus line unless it successfully negotiates via CC.

seba_dos1 4mo ago
They mean bad USB-A to C cables with no resistor on CC line. Of course this is broken junk which will work with some devices and won't with others. I've also seen cables with resistors on both CC lines, which is also broken but in a slightly subtler way.
- exmadscientist 4mo ago
  Right. That phrase "standards-compliant" in the above comments is doing a lot of heavy lifting. A lot of devices are not actually standards-compliant. Some are close. (This may actually be worse.) My experience has been that if the source and sink are broken, they are often hilariously badly broken and it is pretty easy to figure out that they are the problem, if not quite exactly what they've done wrong. But if things are flaky and weird and don't really make sense, it's probably the cable. Try a known-really-seriously-actually-standards-compliantly-good cable and many problems go away, even if the source and sink aren't perfect. (Many sources and sinks aren't standards-compliant because, even though they easily could be, they're trying to work around the other end not being standards-compliant itself, because that's what you've got to do to sell a product. So they're close but not quite there. This is not always ideal.)
- stephen_g 4mo ago
  But it’s not what anyone was talking about. Such a cable should be really quite rare because it’s unlikely to work at all in most situations, whereas devices with USB-C ports that don’t work with PD chargers (due to a cent’s worth of missing Rd resistors) are irritatingly common, because they do work with USB-C to A cables!
  - seba_dos1 4mo ago
    Huh? It seems clear to me that this is what exmadscientist was talking about, any other interpretation just doesn't make sense. And no, such cables would still work in plenty of cases. You usually get them by having them bundled with devices they do work well with. In fact, they always work fine with the kind of devices you mention. These cables aren't as common as USB-C-shaped junk that's missing resistors on the receptacle, but I stumbled upon them anyway and I didn't really try to.
megous 4mo ago
You may wish to re-read the type-c specification, especially 4.5.2.2.3.2: "A USB 2.0 only Sink that doesn’t support accessories and is self-powered or requires only default power and does not support USB PD may transition directly to Attached.SNK when V BUS is detected." or 4.5.2.2.5: "A port that entered this state directly from Unattached.SNK due to detecting V BUS shall not determine orientation or availability of higher than Default USB Power and shall not use USB PD." or 4.5.2.2.11.2: "The port shall transition to Attached.SNK after tCCDebounce if or when V BUS is detected." CC detection, let alone PD negotiation is not needed. You can draw up to 2.5W right away from Vbus and be standard compliant without wiring anything to CC signals. Of course if you try this with a DRP device like a smartphone, you'll get no power. But that's not really an issue for type-c chargers or USB A-C cable assemblies.