Product manual

Spinpoint M9TU-USB 3.0 Product Manual REV 1.0

USB INTERFACE AND USB COMMANDS

Table 6-17: Allowed wMaxPacketSize Values for Different Numbers of Transaction per Microframe

For high-speed bulk and control OUT endpoints, the bInterval field is only used for compliance purposes; the

host controller is not required to change its behavior based on the value in this field.

6.3.6.4.8 String Descriptor

String descriptors are optional. As noted previously, if a device does not support string descriptors, all

references to string descriptors within device, configuration, and interface descriptors must be reset to zero.

String descriptors use UNICODE encodings as defined by The Unicode Standard, Worldwide Character

Encoding, Version 3.0, The Unicode Consortium, Addison-Wesley Publishing Company, Reading,

Massachusetts (URL:

http://www.unicode.com). The strings in a USB device may support multiple languages.

When requesting a string descriptor, the requester specifies the desired language using a sixteenbit language

ID (LANGID) defined by the USB-IF. The list of currently defined USB LANGIDs can be found at

http://www.usb.org/developers/docs.html. String index zero for all languages returns a string descriptor that

contains an array of two-byte LANGID codes supported by the device. Table 6-18 shows the LANGID code

array. A USB device may omit all string descriptors. USB devices that omit all string descriptors must not return

an array of LANGID codes.

The array of LANGID codes is not NULL-terminated. The size of the array (in bytes) is computed by

subtracting two from the value of the first byte of the descriptor.

Table 6-18: String Descriptor Zero, Specifying Language Supported by the Device

The UNICODE string descriptor (shown in Table 6-19) is not NULL-terminated. The string length is

computed by subtracting two from the value of the first byte of the descriptor.

Table 6-19: UNICODE String Descriptor