Atmel SAM9X25, Manual

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33.6.4 USB V2.0 High Speed BUS Transactions
Each transfer results in one or more transactions over the USB bus.
There are five kinds of transactions flowing across the bus in packets:
1. Setup Transaction
2. Data IN Transaction
3. Data OUT Transaction
4. Status IN Transaction
5. Status OUT Transaction
Figure 33-4. Control Read and Write Sequences
A status IN or OUT transaction is identical to a data IN or OUT transaction.
33.6.5 Endpoint Configuration
The endpoint 0 is always a control endpoint, it must be programmed and active in order to be
enabled when the End Of Reset interrupt occurs.
To configure the endpoints:
• Fill the configuration register (UDPHS_EPTCFG) with the endpoint size, direction (IN or
OUT), type (CTRL, Bulk, IT, ISO) and the number of banks.
• Fill the number of transactions (NB_TRANS) for isochronous endpoints.
Note: For control endpoints the direction has no effect.
• Verify that the EPT_MAPD flag is set. This flag is set if the endpoint size and the number of
banks are correct compared to the FIFO maximum capacity and the maximum number of
allowed banks.
• Configure control flags of the endpoint and enable it in UDPHS_EPTCTLENBx according to
“UDPHS Endpoint Control Register” on page 584 .
Control endpoints can generate interrupts and use only 1 bank.
Control Write
Setup TX Data OUT TX Data OUT TX
Data Stage
Control Read
Setup Stage
Setup Stage
Setup TX
Setup TX
No Data
Control
Data IN TX Data IN TX
Status Stage
Status Stage
Status IN TX
Status OUT TX
Status IN TX
Data Stage
Setup Stage Status Stage