DisplayPort: taming the altmode

The DisplayPort altmode is semi-proprietary, but it can absolutely be picked apart if we try. Last time,we found a cool appnote describing the DisplayPort altmode in detail, switched the FUSB302 into packet sniffing mode and got packet captures, learned about PD VDMs (vendor-defined messages), and successfully replayed the captured messages to switch a USB-C port into the DisplayPort altmode. Today, we will go through the seven messages that summon the DisplayPort altmode, implement them, and tie them all into a library - then, figure out the hardware we need to have DisplayPort work in the wild.

USB-C might have its problems, but it's also incredibly cool and versatile.