1 Basic Knowledge

downstream sublink	The collection of lanes between the DFP Tx and the UFP Rx.
DPP	Data Packet Payload. Contains the data packet’s data and a 32 -bit CRC.
DP	Data Packet which consists of a Data Packet Header(DPH) followed by a Data Packet Payload(DPP).
Gen X	Gen X is a generic term used to refer to any of the combinations Gen 1, Gen 2 orGen 1/Gen 2 when the topic is specific to the phy layers but does not need to bespecific to either Gen 1 or Gen 2
Gen X x Y	X refers to the rate of signaling on the wire (Gen 1, Gen 2, etc.) and Y refers to the number of lanes.
LMP	Link Management Packet. A type of header packet used to communicate information between a pair of link partners.
LTSSM	Link Training and Status State Machine
transaction	The IN consists of an ACK TP with a response of NRDY TP, DP, or STALL TP. The OUT consists of a DP with a response of NRDY TP, an ACK TP, or STALL TP.
transfer	One or more bus transactions to move information between a software client and its function.

• The USB 3.2 system architecture is comprised of two simultaneously active buses: a USB 2.0 bus and an Enhanced SuperSpeed bus.

• The nominal signaling data rate for Gen 1 physical layer is 5 Gbps. A Gen 1 transmitter encodes data and control characters into symbols using an 8b/10b code.
• The nominal signaling data rate for the Gen 2 physical layer is 10 Gbps. A Gen 2 transmitter frames data and control bytes (referred to as Symbols) by prepending a 4-bit block identifier to 16 symbols (128 bits) to create a 128b/132b block.

1.1 Difference from USB2.0

• USB 2.0 uses a three-part transaction (Token, Data, and Handshake) while the Enhanced SuperSpeed protocol uses the same three parts differently. For OUTs, the token is incorporated in the data packet; while for INs, the Token is replaced by a handshake.
• USB 2.0 uses a polling model while the Enhanced SuperSpeed protocol uses asynchronous notifications.
• USB 2.0 does not have a Streaming capability while the Enhanced SuperSpeed protocol supports Streaming for bulk endpoints.

1.2 Enhanced Superspeed Packet

• Enhanced SuperSpeed packets start with a 16-byte header. Some packets consist of a header
  only.
• The header is protected by a 16-bit CRC (CRC-16) and ends with a 2-byte link control word.
• There are four basic types of packets: Link Management Packets, Transaction Packets, Data Packets, and Isochronous
• • A Link Management Packet (LMP) only traverses a pair of directly connected ports
    and is primarily used to manage that link.
• • A Transaction Packet (TP) traverses all the links in the path directly connecting the
    host and a device. It is used to control the flow of data packets, configure devices
    and hubs.
• • A Data Packet (DP) traverses all the links in the path directly connecting the host
    and a device. Data Packets consist of two parts: a Data Packet Header (DPH) and a Data Packet Payload (DPP)
• • An Isochronous Timestamp Packet (ITP) is a multicast packet sent by an Enhanced SuperSpeed host/hub to all active links.

1.3 Transfer Description

1.3.1 Data Bursting

• Data Bursting enhances efficiency by eliminating the wait time for acknowledgements on a
  per data packet basis.

1.3.2 IN/OUT Transfers

• A host initiates a transfer by sending an acknowledgement packet (IN) to the device.
• The host tells the device the number of data packets it can send and the sequence number of the first data packet expected from the device
• The acknowledgement packet(IN) also let device implicitly acknowledges the previous data packet that was received successfully.
• An IN transfer on the Enhanced SuperSpeed bus consists of one, or more, IN transactions consisting of one, or more, packets.
• An OUT transfer on the Enhanced SuperSpeed bus consists of one, or more, OUT transactions
  consisting of one, or more, packets.

1.3.2