RM0390 Rev 4 1255/1328
RM0390 USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS)
1264
Internal data flow:
1. An isochronous IN transfer is treated as incomplete in one of the following conditions:
a) The core receives a corrupted isochronous IN token on at least one isochronous
IN endpoint. In this case, the application detects an incomplete isochronous IN
transfer interrupt (IISOIXFR in OTG_GINTSTS).
b) The application is slow to write the complete data payload to the transmit FIFO
and an IN token is received before the complete data payload is written to the
FIFO. In this case, the application detects an IN token received when Tx FIFO
empty interrupt in OTG_DIEPINTx. The application can ignore this interrupt, as it
eventually results in an incomplete isochronous IN transfer interrupt (IISOIXFR in
OTG_GINTSTS) at the end of periodic frame.
The core transmits a zero-length data packet on the USB in response to the
received IN token.
2. The application must stop writing the data payload to the transmit FIFO as soon as
possible.
3. The application must set the NAK bit and the disable bit for the endpoint.
4. The core disables the endpoint, clears the disable bit, and asserts the endpoint disable
interrupt for the endpoint.
Application programming sequence:
1. The application can ignore the IN token received when Tx FIFO empty interrupt in
OTG_DIEPINTx on any isochronous IN endpoint, as it eventually results in an
incomplete isochronous IN transfer interrupt (in OTG_GINTSTS).
2. Assertion of the incomplete isochronous IN transfer interrupt (in OTG_GINTSTS)
indicates an incomplete isochronous IN transfer on at least one of the isochronous IN
endpoints.
3. The application must read the endpoint control register for all isochronous IN endpoints
to detect endpoints with incomplete IN data transfers.
4. The application must stop writing data to the Periodic Transmit FIFOs associated with
these endpoints on the AHB.
5. Program the following fields in the OTG_DIEPCTLx register to disable the endpoint:
– SNAK = 1 in OTG_DIEPCTLx
– EPDIS = 1 in OTG_DIEPCTLx
6. The assertion of the endpoint disabled interrupt in OTG_DIEPINTx indicates that the
core has disabled the endpoint.
– At this point, the application must flush the data in the associated transmit FIFO or
overwrite the existing data in the FIFO by enabling the endpoint for a new transfer
in the next microframe. To flush the data, the application must use the
OTG_GRSTCTL register.
• Stalling non-isochronous IN endpoints
This section describes how the application can stall a non-isochronous endpoint.
Application programming sequence:
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