ST STM32G0 1 Series Reference Manual page 1295

RM0444
Bit 15 VTRX: USB valid transaction received
– Device mode
– Host mode
Universal serial bus full-speed host/device interface (USB)
This bit is set by the hardware when an OUT/SETUP transaction is successfully completed
on this endpoint; the software can only clear this bit. If the CTRM bit in USB_CNTR register
is set accordingly, a generic interrupt condition is generated together with the endpoint
related interrupt condition, which is always activated. The type of occurred transaction, OUT
or SETUP, can be determined from the SETUP bit described below.
A transaction ended with a NAK or STALL handshake does not set this bit, since no data is
actually transferred, as in the case of protocol errors or data toggle mismatches.
This bit is read/write but only 0 can be written, writing 1 has no effect.
This bit is set by the hardware when an IN transaction is successfully completed on this
channel. The software can only clear this bit. If the CTRM bit in USB_CNTR register is set a
generic interrupt condition is generated together with the channel related flag, which is
always activated.
- A transaction ended with a NAK sets this bit and NAK answer is reported to application
reading the NAK state from the STATRX field of this register. One NAKed transaction keeps
pending and is automatically retried by the host at the next frame, or the host can
immediately retry by resetting STATRX state to VALID.
- A transaction ended by STALL handshake sets this bit and the STALL answer is reported
to application reading the STALL state from the STATRX field of this register. Host
application should consequently disable the channel and re-enumerate.
- A transaction ended with ACK handshake sets this bit
If double buffering is disabled, ACK answer is reported by application reading the DISABLE
state from the STATRX field of this register. Host application should read received data from
USBRAM and re-arm the channel by writing VALID to the STATRX field of this register.
If double buffering is enabled, ACK answer is reported by application reading VALID state
from the STATRX field of this register. Host application should read received data from
USBRAM and toggle the DTOGTX bit of this register.
- A transaction ended with error sets this bit
This bit is read/write but only 0 can be written, writing 1 has no effect.
RM0444 Rev 5 1295/1390
1307