... works on XP, Vista, 7 and 8

USBPcap Capture format specification.

Following document describes the LINKTYPE_USBPCAP used in USBPcap. This merely describes the packet data mentioned in pcap file format.

General notes

The types presented below are described in Windows DDK 7.1.0. Short description:

  • UCHAR - 8 bit unsigned value
  • USHORT - 16 bit unsigned value
  • UINT32 - 32 bit unsigned value
  • UINT64 - 64 bit unsigned value
  • ULONG - 64 bit unsigned value
  • USBD_STATUS - 32 bit unsigned value
All multi-byte values are LITTLE-ENDIAN.

Base packet header

The USBPCAP_BUFFER_PACKET_HEADER as defined in USBPcapBuffer.h:

#pragma pack(1)
typedef struct
    USHORT       headerLen; /* This header length */
    UINT64       irpId;     /* I/O Request packet ID */
    USBD_STATUS  status;    /* USB status code
                               (on return from host controller) */
    USHORT       function;  /* URB Function */
    UCHAR        info;      /* I/O Request info */

    USHORT       bus;       /* bus (RootHub) number */
    USHORT       device;    /* device address */
    UCHAR        endpoint;  /* endpoint number and transfer direction */
    UCHAR        transfer;  /* transfer type */

    UINT32       dataLength;/* Data length */
  • headerLen (offset 0) describes the total length, in bytes, of the header (including all transfer-specific header data).
  • irpId (offset 2) is merely a pointer to IRP casted to the UINT64. This value can be used to match the request with respons.
  • status (offset 10) is valid only on return from host-controller. This field corrensponds to the Status member of _URB_HEADER
  • function (offset 14) corrensponds to the Function member of _URB_HEADER
  • info (offset 16) is descibed on the bit-field basis. Currently only the least significant bit (USBPCAP_INFO_PDO_TO_FDO) is defined: it is 0 when IRP goes from FDO to PDO, 1 the other way round. The remaining bits are reserved and must be set to 0.
  • bus (offset 17) is the root hub identifier used to distingush between multiple root hubs.
  • device (offset 19) is USB device number. This field is, contary to the USB specification, 16-bit because the Windows uses 16-bits value for that matter. Check DeviceAddress field of USB_NODE_CONNECTION_INFORMATION
  • endpoint (offset 21) is the endpoint number used on the USB bus (the MSB describes transfer direction)
  • transfer (offset 22) determines the transfer type and thus the header type. See below for details.
  • dataLength (offset 23) specifies the total length of transfer data to follow directly after the header (at offset headerLen).

Transfer-specific headers

All transfer-specific headers inherit the USBPCAP_BUFFER_PACKET_HEADER, so first there is the USBPCAP_BUFFER_PACKET_HEADER, then (if any) additional transfer-specific header data and then the transfer data.


When function is equal to USBPCAP_TRANSFER_ISOCHRONOUS (0) the header type is USBPCAP_BUFFER_ISOCH_HEADER

/* Note about isochronous packets:
 *   packet[x].length, packet[x].status and errorCount are only relevant
 *   when USBPCAP_INFO_PDO_TO_FDO is set
 *   packet[x].length is not used for isochronous OUT transfers.
 * Buffer data is attached to:
 *   * for isochronous OUT transactions (write to device)
 *       Requests (USBPCAP_INFO_PDO_TO_FDO is not set)
 *   * for isochronous IN transactions (read from device)
 *       Responses (USBPCAP_INFO_PDO_TO_FDO is set)
#pragma pack(1)
typedef struct
    ULONG        offset;
    ULONG        length;
    USBD_STATUS  status;

#pragma pack(1)
typedef struct
    ULONG                         startFrame;
    ULONG                         numberOfPackets;
    ULONG                         errorCount;
    USBPCAP_BUFFER_ISO_PACKET     packet[1];


When function is equal to USBPCAP_TRANSFER_INTERRUPT (1) the header type is USBPCAP_BUFFER_PACKET_HEADER


When function is equal to USBPCAP_TRANSFER_CONTROL (2) the header type is USBPCAP_BUFFER_CONTROL_HEADER


#pragma pack(1)
typedef struct
    UCHAR                         stage;
Where stage determines the control transfer stage.


When function is equal to USBPCAP_TRANSFER_BULK (3) the header type is USBPCAP_BUFFER_PACKET_HEADER