ST STM32F40 Series Reference Manual page 1149

USB on-the-go full-speed (OTG_FS)
Application programming sequence:
1. Program the OTG_FS_DIEPCTLx register with the endpoint characteristics and set the
CNAK and EPENA bits.
2. Write the data to be transmitted in the next frame to the transmit FIFO.
3. Asserting the ITTXFE interrupt (in OTG_FS_DIEPINTx) indicates that the application
has not yet written all data to be transmitted to the transmit FIFO.
4. If the interrupt endpoint is already enabled when this interrupt is detected, ignore the
interrupt. If it is not enabled, enable the endpoint so that the data can be transmitted on
the next IN token attempt.
5. Asserting the XFRC interrupt (in OTG_FS_DIEPINTx) with no ITTXFE interrupt in
OTG_FS_DIEPINTx indicates the successful completion of an isochronous IN transfer.
A read to the OTG_FS_DIEPTSIZx register must give transfer size = 0 and packet
count = 0, indicating all data were transmitted on the USB.
6. Asserting the XFRC interrupt (in OTG_FS_DIEPINTx), with or without the ITTXFE
interrupt (in OTG_FS_DIEPINTx), indicates the successful completion of an interrupt
IN transfer. A read to the OTG_FS_DIEPTSIZx register must give transfer size = 0 and
packet count = 0, indicating all data were transmitted on the USB.
7. Asserting the incomplete isochronous IN transfer (IISOIXFR) interrupt in
OTG_FS_GINTSTS with none of the aforementioned interrupts indicates the core did
not receive at least 1 periodic IN token in the current frame.
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Incomplete isochronous IN data transfers
This section describes what the application must do on an incomplete isochronous IN data
transfer.
Internal data flow:
1. An isochronous IN transfer is treated as incomplete in one of the following conditions:
a)
b)
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.
1149/1422
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_FS_GINTSTS).
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 TxFIFO
empty interrupt in OTG_FS_DIEPINTx. The application can ignore this interrupt,
as it eventually results in an incomplete isochronous IN transfer interrupt
(IISOIXFR in OTG_FS_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.
Doc ID 018909 Rev 4
RM0090