ST STM32F412 Reference Manual page 1104

USB on-the-go full-speed (OTG_FS)
1. The internal data flow for isochronous OUT endpoints is the same as that for non-
isochronous OUT endpoints, but for a few differences.
2. When an isochronous OUT endpoint is enabled by setting the endpoint enable and
clearing the NAK bits, the Even/Odd frame bit must also be set appropriately. The core
receives data on an isochronous OUT endpoint in a particular frame only if the
following condition is met:
–
3. When the application completely reads an isochronous OUT data packet (data and
status) from the receive FIFO, the core updates the RXDPID field in OTG_DOEPTSIZx
with the data PID of the last isochronous OUT data packet read from the receive FIFO.
Application programming sequence:
1. Program the OTG_DOEPTSIZx register for the transfer size and the corresponding
packet count
2. Program the OTG_DOEPCTLx register with the endpoint characteristics and set the
endpoint enable, ClearNAK, and Even/Odd frame bits.
–
–
–
3. Wait for the RXFLVL interrupt (in OTG_GINTSTS) and empty the data packets from the
receive FIFO
–
4. The assertion of the XFRC interrupt (in OTG_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 INCOMPISOOUT interrupt in OTG_GINTSTS.
6. Read the OTG_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:
–
–
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_DOEPINTx) may not
always be asserted. If the core drops isochronous OUT data packets, the application
1104/1163
EONUM (in OTG_DOEPCTLx) = FNSOF[0] (in OTG_DSTS)
EPENA = 1
CNAK = 1
EONUM = (0: Even/1: Odd)
This step can be repeated many times, depending on the transfer size.
RXDPID = DATA0 (in OTG_DOEPTSIZx) and the number of USB packets in
which this payload was received = 1
RXDPID = DATA1 (in OTG_DOEPTSIZx) and the number of USB packets in
which this payload was received = 2
The number of USB packets in which this payload was received =
Application programmed initial packet count – core updated final packet count
RM0402 Rev 6
RM0402