ST STM32L4x6 Reference Manual page 1574

USB on-the-go full-speed (OTG_FS)
Bit 28 SD0PID: Set DATA0 PID
SEVNFRM: Set even frame
Bit 27 SNAK: Set NAK
Bit 26 CNAK: Clear NAK
Bits 25:22 TXFNUM: Tx FIFO number
Bit 21 STALL: STALL handshake
Bit 20 Reserved, must be kept at reset value.
Bits 19:18 EPTYP: Endpoint type
Bit 17 NAKSTS: NAK status
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Applies to interrupt/bulk IN endpoints only.
Writing to this field sets the endpoint data PID (DPID) field in this register to DATA0.
Applies to isochronous IN endpoints only.
Writing to this field sets the Even/Odd frame (EONUM) field to even frame.
A write to this bit sets the NAK bit for the endpoint.
Using this bit, the application can control the transmission of NAK handshakes on an
endpoint. The core can also set this bit for OUT endpoints on a Transfer completed interrupt,
or after a SETUP is received on the endpoint.
A write to this bit clears the NAK bit for the endpoint.
These bits specify the FIFO number associated with this endpoint. Each active IN endpoint
must be programmed to a separate FIFO number.
This field is valid only for IN endpoints.
Applies to non-control, non-isochronous IN endpoints only (access type is rw).
The application sets this bit to stall all tokens from the USB host to this endpoint. If a NAK
bit, Global IN NAK, or Global OUT NAK is set along with this bit, the STALL bit takes priority.
Only the application can clear this bit, never the core.
Applies to control endpoints only (access type is rs).
The application can only set this bit, and the core clears it, when a SETUP token is received
for this endpoint. If a NAK bit, Global IN NAK, or Global OUT NAK is set along with this bit,
the STALL bit takes priority. Irrespective of this bit's setting, the core always responds to
SETUP data packets with an ACK handshake.
This is the transfer type supported by this logical endpoint.
00: Control
01: Isochronous
10: Bulk
11: Interrupt
It indicates the following:
0: The core is transmitting non-NAK handshakes based on the FIFO status.
1: The core is transmitting NAK handshakes on this endpoint.
When either the application or the core sets this bit:
For non-isochronous IN endpoints: The core stops transmitting any data on an IN endpoint,
even if there are data available in the Tx FIFO.
For isochronous IN endpoints: The core sends out a zero-length data packet, even if there
are data available in the Tx FIFO.
Irrespective of this bit's setting, the core always responds to SETUP data packets with an
ACK handshake.
DocID024597 Rev 3
RM0351