Hacker News new | ask | show | jobs
by lxgr 256 days 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.
2 comments
jauntywundrkind 256 days 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/68...

link
lxgr 256 days 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.

link
userbinator 256 days 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.

link
lxgr 256 days 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.

link