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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 hav

by 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
It's a protocol they designed, so they could do whatever they wanted between the initial linkup and carrying data, including link training. but denying the complexity of the problem space can be a hint that you don’t sufficiently understand it ...or that I understand more of it simultaneously to see that it could be made much simpler.
- lxgr 1y ago
  They did in fact not design all protocols running over USB-C, as I’ve mentioned. This allows it to work with other ports without putting a complete link speed protocol converter into the cable or adapter.

by lxgr 1y ago

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

It's a protocol they designed, so they could do whatever they wanted between the initial linkup and carrying data, including link training. but denying the complexity of the problem space can be a hint that you don’t sufficiently understand it ...or that I understand more of it simultaneously to see that it could be made much simpler.

lxgr 1y ago
They did in fact not design all protocols running over USB-C, as I’ve mentioned. This allows it to work with other ports without putting a complete link speed protocol converter into the cable or adapter.