The packet provides the status of the data packet received. The device sends this packet in case of OUT transaction. Handshake Packet: This packet is sent by Host if there is an IN transaction. For IN transaction, the device sends the data and for OUT transaction, the Host sends the data. It used Data1 PID for the first packet and additional alternate Data0/Data1. The data may be sent in more than one packet if the data length exceeds the maximum value of packet length. The length of the data is already specified by the wLength field. This packet is sent by host.ĭata Packet: This packet is used to transfer the requested data. Token Packet: This packet contains PID that specifies whether the transaction is IN or OUT, device address, endpoint and CRC. Each transaction contains three packets, Token, Data and Handshake. It contains various IN or OUT transactions. In this stage the requested data is transferred. This is the second and an optional stage in Control Transfer. 2: Image showing Data Format of Setup Transaction 2. For interface, bit 7-0 represents the interface number.įig. For endpoint, bit 3-0 represents the endpoint number and bit 7 represents the direction 0 : OUT 1 : IN. The typical use includes passing the endpoint or interface number. wIndex – This field also specifies the information that needs to be passed from host to device with the request.For example, in Set_Address request, wValue contains the device address. wValue – This field specifies the information that needs to be passed from host to device with the request.For example, bRequest value can be used to select one of the standard USB requests. The unique value of the bRequest specifies one of the selected requests. bRequest – The type of request can be selected by bmRequestType.Bit 4-0 specifies the recipient for the request. Bit 7 represents the direction of data flow in data stage. bmRequestType – This field provides information related to data direction, type of request, and the designated recipient.The contents of data payload includes following fields : This packet is sent by host.ĭata Packet : It contains Data0 PID. The address is updated after assigning a unique address to the device. The default endpoint and device address 0 is used. Token Packet: It contains Setup PID (Packet Identifier), device address, endpoint and CRC. The transaction consists of three packets – Token, Data and Handshake. The setup transaction is used in this stage. The Control Transfer starts with a Setup Stage. As discussed before while discussing USB protocol, the Control Transfer consists of three transactions – Setup transaction, Data transaction (optional) and Status transaction. Therefore, the first request that is prompted by the host to the peripheral just involves a control transfer. The default endpoint is endpoint 0 which is bidirectional and used for control transfers. That is the reason, it is used for sending requests and obtaining the descriptors. The Control Transfer is the only transfer type which is supported even when the device is yet not configured. The subsequent descriptors implements the functioning, the peripheral is meant for. The device descriptor is the first descriptor sent to the host and it helps configuring the peripheral with respect to the host. The Descriptors contain the information required for identifying and configuring the peripheral device, implementing the interfaces and setting endpoints. The peripheral responds by sending Descriptors. When a USB peripheral is connected to a host device, the host sends queries in the form of requests. This package also enables other advanced analysis capabilities including USB 2.0 automated signal quality testing, mask testing, and frequency response analysis (Bode plots) to help test and debug high-speed digital signals, such as USB 2.0.In the previous article of this series, USB Descriptors were discussed. The USB software package for Keysight’s InfiniiVision 3000T and 3000G X-Series oscilloscopes enables USB 2.0 low-, full-, and hi-speed protocol triggering and decode, as well as USB PD (Power Delivery) trigger and decode. Precision differential probes available.Compatible with segmented memory acquisition with decoding on every captured packet.Serial decode trace time-correlated with USB waveforms.
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