ST STM32L4+ Series Reference Manual page 2242

USB on-the-go full-speed (OTG_FS)
time can be obtained from the transceiver vendor and varies from one transceiver to
another.
3. The OTG_FS core informs the PHY to speed up V
4. The application initiates SRP by writing the session request bit in the OTG control and
status register. The OTG_FS controller perform data-line pulsing followed by V
pulsing.
5. The host detects SRP from either the data-line or V
The PHY indicates V
6. The OTG_FS controller performs V
The host starts a new session by turning on V
OTG_FS controller interrupts the application by setting the session request success
status change bit in the OTG interrupt status register. The application reads the session
request success bit in the OTG control and status register.
7. When the USB is powered, the OTG_FS controller connects, completing the SRP
process.
A-device host negotiation protocol
HNP switches the USB host role from the A-device to the B-device. The application must set
the HNP-capable bit in the core USB configuration register to enable the OTG_FS controller
to perform HNP as an A-device.
1. DPPULLDOWN = signal from core to PHY to enable/disable the pull-down on the DP line inside the PHY.
DMPULLDOWN = signal from core to PHY to enable/disable the pull-down on the DM line inside the PHY.
The following points refer and describe the signal numeration shown in the
1. The OTG_FS controller sends the B-device a SetFeature b_hnp_enable descriptor to
enable HNP support. The B-device's ACK response indicates that the B-device
supports HNP. The application must set host Set HNP enable bit in the OTG control
2242/2301
power-on to the device.
BUS
pulsing.
BUS
Figure 640. A-device HNP
RM0432 Rev 6
discharge.
BUS
pulsing, and turns on V
BUS
, indicating SRP success. The
BUS
RM0432
BUS
.
BUS
Figure 640: