Figure 372. B-Device Hnp - ST STM32F207 Series Reference Manual

USB on-the-go full-speed (OTG_FS)
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 controller to
perform HNP as a B-device.
OTG core
DP
DM
DPPULLDOWN
DMPULLDOWN
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.
1. The A-device sends the SetFeature b_hnp_enable descriptor to enable HNP support.
The OTG_FS controller's ACK response indicates that it supports HNP. The application
must set the device HNP enable bit in the OTG Control and status register to indicate
HNP support.
The application sets the HNP request bit in the OTG Control and status register to
indicate to the OTG_FS controller to initiate HNP.
2. When it has finished using the bus, the A-device suspends by writing the Port suspend
bit in the host port control and status register.
The OTG_FS controller sets the Early suspend bit in the Core interrupt register after 3
ms of bus idleness. Following this, the OTG_FS controller sets the USB suspend bit in
the Core interrupt register.
The OTG_FS controller disconnects and the A-device detects SE0 on the bus,
indicating HNP. The OTG_FS controller asserts the DP pull down and DM pull down in
the PHY to indicate its assumption of the host role.
The A-device responds by activating its OTG_FS_DP pull-up resistor within 3 ms of
detecting SE0. The OTG_FS controller detects this as a connect.
The OTG_FS controller sets the host negotiation success status change interrupt in the
OTG Interrupt status register, indicating the HNP status. The application must read the
host negotiation success bit in the OTG Control and status register to determine host
negotiation success. The application must read the current Mode bit in the Core
interrupt register (OTG_FS_GINTSTS) to determine host mode operation.
3. The application sets the reset bit (PRST in OTG_FS_HPRT) and the OTG_FS
controller issues a USB reset and enumerates the A-device for data traffic.
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Figure 372. B-device HNP

1
Device
Suspend 2 4
3
RM0033 Rev 9
Host
6
5
Reset Traffic
Traffic
RM0033
Device
8
Connect
7
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