ST STM32G0 1 Series Reference Manual page 1296

Universal serial bus full-speed host/device interface (USB)
Bit 14 DTOGRX: Data Toggle, for reception transfers
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If the endpoint/channel is not isochronous, this bit contains the expected value of the data
toggle bit (0 = DATA0, 1 = DATA1) for the next data packet to be received. Hardware toggles
this bit, when the ACK handshake is sent following a data packet reception having a
matching data PID value; if the endpoint is defined as a control one, hardware clears this bit
at the reception of a SETUP PID received from host (in device) or acknowledged by device
(in host).
If the endpoint/channel is using the double-buffering feature this bit is used to support packet
buffer swapping too (Refer to
Device mode).
If the endpoint/channel is isochronous, this bit is used only to support packet buffer
swapping for data transmission since no data toggling is used for this kind of
channels/endpoints and only DATA0 packet are transmitted (Refer to
Isochronous transfers in Device
packet reception, since no handshake is used for isochronous transfers.
This bit can also be toggled by the software to initialize its value (mandatory when the
endpoint is not a control one) or to force specific data toggle/packet buffer usage. When the
application software writes 0, the value of DTOGRX remains unchanged, while writing 1
makes the bit value toggle. This bit is read/write but it can be only toggled by writing 1.
Section 37.5.3: Double-buffered endpoints and usage in
mode). Hardware toggles this bit just after the end of data
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Section 37.5.5: