Definitions - GoARKS/USB-C-thru GitHub Wiki

Rp: A pull up resistor on the CC line and is used to indicate the capability of a device as a power source and it’s current capability. The Rp value is also used to indicate the current capability of the source.

Rd: A pull down resistor on the CC line and is used to indicate the capability of a device as power sink.

Ra: A pull down resistor on the CC line and is used to indicate that the device requires VConn supply on a CC line.

Source: Devices that present Rp on the CC pin and provide 5V on the VBus pin upon connection are called USB Type-C source devices

Sink: Devices that present Rd on the CC pin and consume 5V on the VBus pin when connected are called USB Type-C Sink devices.

DFP: Downstream Facing Port or DFP, in USB terminology, is a port on a USB host. A port is said to be a DFP in a USB Type-C context when it presents Rp on its CC line and is able to provide VBus.

UFP: Upstream Facing Port or UFP, in USB terminology, is a port on a USB device. A port is said to be a UFP in a USB Type-C context when it presents Rd on its CC line and consumes VBus.

DRP: Dual Role Port or DRP is a port that can operate as both USB host and USB device. We can call this an OTG port in a broader sense. This port presents Rp when in host mode and Rd when in device mode. Before a connection, the CC lines will be toggling between Rp and Rd with predefined timing parameters.

Electronically Marked Cable: Electronically Marked Cable or EMCA are USB Type-C cables that can respond to commands sent to it and may perform signal conditioning with built-in electronics.

Active cable: EMCA cables that perform signal conditioning using inbuilt electronics are called Active EMCA.| Passive Cable: A passive cable is a USB Type-C cable (could be EMCA or non EMCA) that does not implement signal conditioning.

Alternate Mode In an alternate mode the USB Type-C signals are repurposed to function as an interface other than USB. Alternate modes are possible for devices that support USB PD functionality as well.

Consumer: A consumer is a device, which can be a USB host or a USB device that consumes power from the peer through a negotiated contract. A consumer has to present Rd on its CC line.

Provider: A provider is a device, which can be a USB host or a USB device that provides power to the peer after a successful contract. A provider has to present Rp on its CC line.

Data Role Swap: A Data Role Swap is a provision provided by the USB-PD specification that allows a USB device to change host to device and vice versa. In legacy terms one can correlate a Data Role Swap equivalent to OTG. In USB-PD terms when a Data Role Swap is successful a DFP becomes a UFP and vice versa. It is important to note that Rp or Rd presented on the CC line does not get swapped.

Power Role Swap: A Power Role Swap is a provision provided by the USB-PD specification that allows a USB device to swap its role from a provider to a consumer and vice versa. After a successful Power Role Swap the CC line changes to Rd for a source that changes its role to sink. And the CC lines changes to Rp for a sink that changes its role to source. It is important to note that Power Role Swap does not affect the data role of the device.

Contract: A contract is an agreement between USB-PD port partners (Provider/Consumer), which negotiates power between a source and a sink. A contract is achieved by PD protocol command / responses. It is also necessary for further PD negotiations like for alternate modes etc. A contract, in a very broader sense, is a session for power.

Explicit Contract: A Contract that is achieved through the following USB-PD protocol negotiations is called explicit contract: [1] Sink sending a Request message, [2] Source accepting (i) and sending an Accept message, and [3] Subsequently source sending the command PS_RDY (Power Source Ready). An explicit contract can be renegotiated and is a mandatory modal activity as explained below.

Implicit Contract: Implicit contract is a power level agreement between port pairs, which is not a result of power negotiation process. An implicit contract is a result of power role swap negotiations. A device will transition to explicit contract after the implicit contract.

SOP Packet: SOP Packet or the Start Of Packet is a bit pattern that indicates the destination of the transmitted packet and also indicates the packet start.

SOP*: SOP* Communications between a VConn Source (DFP/UFP) and the Cable Plugs.

SOP': When no Contract or an Implicit Contract is in place (e.g. after a Power Role Swap or Fast Role Swap) the Source (which can be either the DFP or UFP but must also be the VConn Source) can communicate with a Cable Plug using SOP' packets in order to discover its characteristics.

SOP'': When an Explicit Contract is in place the VConn Source (either the DFP or the UFP) can communicate with the Cable Plug(s) using SOP’/SOP’’ Packets.