CHAPTER 12 USB FUNCTION CONTROLLER (USBF)
Preliminary User’s Manual U19014EJ1V0UD
278
(c) GET_DESCRIPTOR() request
If the subject descriptor has a length that is a multiple of wMaxPacketSize, a Null packet is returned to
indicate the end of the data stage. If the length of the descriptor at this time is less than the wLength value,
the entire descriptor is returned; if the length of the descriptor is greater than the wLength value, the
descriptor up to the wLength value is returned.
•
Default
state:
The value stored in UF0 device descriptor register n (UF0DDn) and UF0
configuration/interface/endpoint descriptor register m (UF0CIEm) is returned (n = 0 to
17, m = 0 to 255) when the GET_DESCRIPTOR() request has been received.
•
Addressed state: The value stored in the UF0DDn register and UF0CIEm register is returned when the
GET_DESCRIPTOR() request has been received.
•
Configured state: The value stored in the UF0DDn register and UF0CIEm register is returned when the
GET_DESCRIPTOR() request has been received.
A descriptor of up to 256 bytes can be stored in the UF0CIEm register. To return a descriptor of more than
256 bytes, set the CDCGDST bit of the UF0MODC register to 1 and process the GET_DESCRIPTOR()
request by FW.
Store the value of the total number of bytes of the descriptor set by the UF0CIEm register – 1 in the UF0
descriptor length register (UF0DSCL). The transfer data is controlled by the value of this data + 1 and
wLength.
(d) GET_INTERFACE() request
If either of wValue and wLength is other than that shown in Table 12-3, or if wIndex is other than that set by
the UF0 active interface number register (UF0AIFN), a STALL response is made in the data stage.
•
Default state:
A STALL response is made in the data stage when the GET_INTERFACE() request
has been received.
•
Addressed state: A STALL response is made in the data stage when the GET_INTERFACE() request
has been received.
•
Configured state: The value stored in the UF0 interface n register (UF0IFn) corresponding to the wIndex
value is returned (n = 0 to 4) when the GET_INTERFACE() request has been received.
electronic components distributor