USB on-the-go full-speed (OTG_FS) RM0033
1080/1381 RM0033 Rev 9
Application programming sequence
1. Program the OTG_FS_DOEPTSIZx register for the transfer size and the corresponding
packet count
2. Program the OTG_FS_DOEPCTLx register with the endpoint characteristics and set
the Endpoint Enable, ClearNAK, and Even/Odd frame bits.
– EPENA = 1
–CNAK=1
– EONUM = (0: Even/1: Odd)
3. Wait for the RXFLVL interrupt (in OTG_FS_GINTSTS) and empty the data packets
from the receive FIFO
– This step can be repeated many times, depending on the transfer size.
4. The assertion of the XFRC interrupt (in OTG_FS_DOEPINTx) marks the completion of
the isochronous OUT data transfer. This interrupt does not necessarily mean that the
data in memory are good.
5. This interrupt cannot always be detected for isochronous OUT transfers. Instead, the
application can detect the IISOOXFRM interrupt in OTG_FS_GINTSTS.
6. Read the OTG_FS_DOEPTSIZx register to determine the size of the received transfer
and to determine the validity of the data received in the frame. The application must
treat the data received in memory as valid only if one of the following conditions is met:
– RXDPID = D0 (in OTG_FS_DOEPTSIZx) and the number of USB packets in
which this payload was received = 1
– RXDPID = D1 (in OTG_FS_DOEPTSIZx) and the number of USB packets in
which this payload was received = 2
– RXDPID = D2 (in OTG_FS_DOEPTSIZx) and the number of USB packets in
which this payload was received = 3
The number of USB packets in which this payload was received =
Application programmed initial packet count – Core updated final packet count
The application can discard invalid data packets.
• Incomplete isochronous OUT data transfers
This section describes the application programming sequence when isochronous OUT data
packets are dropped inside the core.
Internal data flow
1. For isochronous OUT endpoints, the XFRC interrupt (in OTG_FS_DOEPINTx) may not
always be asserted. If the core drops isochronous OUT data packets, the application
could fail to detect the XFRC interrupt (OTG_FS_DOEPINTx) under the following
circumstances:
– When the receive FIFO cannot accommodate the complete ISO OUT data packet,
the core drops the received ISO OUT data
– When the isochronous OUT data packet is received with CRC errors
– When the isochronous OUT token received by the core is corrupted
– When the application is very slow in reading the data from the receive FIFO
2. When the core detects an end of periodic frame before transfer completion to all
isochronous OUT endpoints, it asserts the incomplete Isochronous OUT data interrupt
(IISOOXFRM in OTG_FS_GINTSTS), indicating that an XFRC interrupt (in
OTG_FS_DOEPINTx) is not asserted on at least one of the isochronous OUT
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