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Spinpoint M8U-Internal Product Manual REV 3.4
74
INSTALLATION
When an endpoint supports isochronous transfers, the endpoint may also require per-frame transfers to vary
in size according to a specific pattern. The host and the endpoint must agree on which frame the repeating
pattern begins. The number of the frame in which the pattern began is returned to the host.
If a high-speed device supports the Synch Frame request, it must internally synchronize itself to the zeroth
microframe and have a time notion of classic frame. Only the frame number is used to synchronize and
reported by the device endpoint (i.e., no microframe number). The endpoint must synchronize to the zeroth
microframe.
This value is only used for isochronous data transfers using implicit pattern synchronization. If wValue is
non-zero or wLength is not two, then the behavior of the device is not specified.
If the specified endpoint does not support this request, then the device will respond with a Request Error.
Default state: Device behavior when this request is received while the device is in the Default state is not
specified
.
Address state: The device shall respond with a Request Error.
Configured state: This is a valid request when the device is in the Configured state.
6.3.6.4 Standard USB Descriptor
The standard descriptors defined in this specification may only be modified or extended by revision of the
Universal Serial Bus Specification.
Note: An extension to the USB 1.0 standard endpoint descriptor has been published in Device Class
Specification for Audio Devices Revision 1.0. This is the only extension defined outside USB Specification
that is allowed. Future revisions of the USB Specification that extend the standard endpoint descriptor will do
so as to not conflict with the extension defined in the Audio Device Class Specification Revision 1.0.
6.3.6.4.1 Standard USB Descriptor Overview
USB devices report their attributes using descriptors. A descriptor is a data structure with a defined format.
Each descriptor begins with a byte-wide field that contains the total number of bytes in the descriptor
followed by a byte-wide field that identifies the descriptor type.
Using descriptors allows concise storage of the attributes of individual configurations because each
configuration may reuse descriptors or portions of descriptors from other configurations that have the same
characteristics. In this manner, the descriptors resemble individual data records in a relational database.
Where appropriate, descriptors contain references to string descriptors that provide displayable information
describing a descriptor in human-readable form. The inclusion of string descriptors is optional. However, the
reference fields within descriptors are mandatory. If a device does not support string descriptors, string
reference
fields must be reset to zero to indicate no string descriptor is available.
If a descriptor returns with a value in its length field that is less than defined by this specification, the
descriptor is invalid and should be rejected by the host. If the descriptor returns with a value in its length field
that is greater than defined by this specification, the extra bytes are ignored by the host, but the next
descriptor is located using the length returned rather than the length expected.
A device may return class- or vendor-specific descriptors in two ways:
1. If the class or vendor specific descriptors use the same format as standard descriptors (e.g., start with a
length byte and followed by a type byte), they must be returned interleaved with standard descriptors in the
configuration information returned by a GetDescriptor(Configuration) request. In this case, the class or
vendor-specific descriptors must follow a related standard descriptor they modify or extend.
2. If the class or vendor specific descriptors are independent of configuration information or use a
nonstandard format, a GetDescriptor() request specifying the class or vendor specific descriptor type and
index may be used to retrieve the descriptor from the device. A class or vendor specification will define the
appropriate way to retrieve these descriptors.