Endpoint Queue Head - Freescale Semiconductor MPC8313E Family Reference Manual

Universal Serial Bus Interface
The USB DR module includes DCD software called the USB 2.0 Device API. The device API provides
an easy to use Application Program Interface for developing device (peripheral) applications. The device
API incorporates and abstracts for the application developer all of the elements of the program interface.
Up to
32 Elements
ENDPOINTLISTADDR
16.7.1

Endpoint Queue Head

The device Endpoint Queue Head (dQH) is where all transfers are managed. The dQH is a 48-byte data
structure, but must be aligned on 64-byte boundaries. During priming of an endpoint, the dTD (device
transfer descriptor) is copied into the overlay area of the dQH, which starts at the nextTD pointer DWord
and continues through the end of the buffer pointers DWords. After a transfer is complete, the dTD status
DWord is updated in the dTD pointed to by the currentTD pointer. While a packet is in progress, the
overlay area of the dQH is used as a staging area for the dTD so that the Device Controller can access
needed information with little minimal latency.
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
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Endpoint QH 1—Out
Endpoint QH 0—In
Endpoint QH 0—Out
Endpoint Queue Heads
Figure 16-60. Endpoint Queue Head Organization
Endpoint Transfer Descriptor
Transfer
Transfer
Buffer
Buffer
Pointer
Transfer Buffer Pointer
Transfer Buffer Pointer
Transfer Buffer Pointer
Transfer
Buffer
Transfer
Buffer
Transfer
Buffer
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