isoc_frame_no

Specify this field when the overall transfer must start from a specific frame number. The value of this field must be greater than the current frame number. Use usb_get_current_frame_number(9F) to find the current frame number. Note that the current frame number is a moving target. For low-speed and full-speed buses, the current frame is new each millisecond. For high-speed buses, the current frame is new each 0.125 millisecond. Set the USB_ATTR_ISOC_START_FRAME attribute so that the isoc_frame_no field is recognized.

To ignore this frame number field and start as soon as possible, set the USB_ATTR_ISOC_XFER_ASAP flag.

isoc_pkts_count

This field is the number of packets in the request. This value is bounded by the value returned by the usb_get_max_pkts_per_isoc_request(9F) function and by the size of the isoc_pkt_descr array (see below). The number of bytes transferable with this request is equal to the product of this isoc_pkts_count value and the wMaxPacketSize value of the endpoint.

isoc_pkts_length

This field is the sum of the lengths of all packets of the request. This value is set by the initiator. This value should be set to zero so that the sum of isoc_pkts_length in the isoc_pkt_descr list will be used automatically and no check will be applied to this element.

isoc_error_count

This field is the number of packets that completed with errors. This value is set by the USBA 2.0 framework. 

isoc_pkt_descr

This field points to an array of packet descriptors that define how much data to transfer per packet. For an outgoing request, this value defines a private queue of sub-requests to process. For an incoming request, this value describes how the data arrived in pieces. The client driver allocates these descriptors for outgoing requests. The framework allocates and initializes these descriptors for incoming requests. Descriptors in this array contain framework-initialized fields that hold the number of bytes actually transferred and the status of the transfer. See the usb_isoc_request(9S) man page for more details.