ST STM32F446 Series Reference Manual page 1262

USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS)
control and status register to indicate to the OTG_FS/OTG_HS controller that the B-
device supports HNP.
2. When it has finished using the bus, the application suspends by writing the port
suspend bit in the host port control and status register.
3. When the B-device observes a USB suspend, it disconnects, indicating the initial
condition for HNP. The B-device initiates HNP only when it must switch to the host role;
otherwise, the bus continues to be suspended.
The OTG_FS/OTG_HS controller sets the host negotiation detected interrupt in the
OTG interrupt status register, indicating the start of HNP.
The OTG_FS/OTG_HS controller deasserts the DM pull down and DM pull down in the
PHY to indicate a device role. The PHY enables the OTG_DP pull-up resistor to
indicate a connect for B-device.
The application must read the current mode bit in the OTG control and status register
to determine device mode operation.
4. The B-device detects the connection, issues a USB reset, and enumerates the
OTG_FS/OTG_HS controller for data traffic.
5. The B-device continues the host role, initiating traffic, and suspends the bus when
done.
The OTG_FS/OTG_HS controller sets the early suspend bit in the core interrupt
register after 3 ms of bus idleness. Following this, the OTG_FS/OTG_HS controller
sets the USB suspend bit in the core interrupt register.
6. In Negotiated mode, the OTG_FS/OTG_HS controller detects the suspend,
disconnects, and switches back to the host role. The OTG_FS/OTG_HS controller
asserts the DM pull down and DM pull down in the PHY to indicate its assumption of
the host role.
7. The OTG_FS/OTG_HS controller sets the connector ID status change interrupt in the
OTG interrupt status register. The application must read the connector ID status in the
OTG control and status register to determine the OTG_FS/OTG_HS controller
operation as an A-device. This indicates the completion of HNP to the application. The
application must read the Current mode bit in the OTG control and status register to
determine host mode operation.
8. The B-device connects, completing the HNP process.
B-device host negotiation protocol
HNP switches the USB host role from B-device to A-device. The application must set the
HNP-capable bit in the core USB configuration register to enable the OTG_FS/OTG_HS
controller to perform HNP as a B-device.
1262/1328 RM0390 Rev 4
RM0390