USB Power delivery for Alternative mode

USB PD除了電源需求的溝通，也可以用來溝通彼此的信號需求，例如使用原來

Type-C USB3.x的通道，用來傳輸Displayport,PCIE等高速訊號。

下面是DFP端與UFP端交握的過程，DFP端利用PD的protocol，來得知對方是什麼

樣的裝置，UFP端也會讓DFP端知道它支援那些高速訊號，再由DFP端來決定要

提供USB或Displayport或PCIE給UFP端。

1.Discover Identity VDM command

 Send VDM 1xxFh,FF00h,8001h

 Receive VDM from UFP side and check if ACK bits is “01”h

 Check device or Cable spec


2. Discover SVIDs VDM command

   Send VDM,1xxFh,FF00h,8002h

  Receive VDM from UFP side and check if ACK bits is “01”h

  Check device SVID

3.Discover Modes VDM command

Send VDM,1xxFh,xxxxh (SVID),8003h

Receive VDM from UFP side and check if ACK bits is “01”h

Check device Mode

4.Enter Mode

Check which mode you want to enter.
Send VDM,1xxFh,xxxxh (SVID),8x04h (x is object mode position)

Receive VDM from UFP side and check if ACK bits is “01”h

5.Control Mux

Control the Super speed Mux by MCU or PD IC. Depend
on the mode you want to enter.

Reference
1. USB PD 2.0
2. VESA, DisplayPort Technology Update
https://www.vesa.org/wp-content/uploads/2015/07/VESA-Taiwan-Press-61115.pdf