DocID13902 Rev 15 828/1128
RM0008 USB on-the-go full-speed (OTG_FS)
957
28.5.2 Peripheral states
Powered state
The V
BUS
input detects the B-Session valid voltage by which the USB peripheral is allowed
to enter the powered state (see USB2.0 par9.1). The OTG_FS then automatically connects
the DP pull-up resistor to signal full-speed device connection to the host and generates the
session request interrupt (SRQINT bit in OTG_FS_GINTSTS) to notify the powered state.
The V
BUS
input also ensures that valid V
BUS
levels are supplied by the host during USB
operations. If a drop in V
BUS
below B-session valid happens to be detected (for instance
because of a power disturbance or if the host port has been switched off), the OTG_FS
automatically disconnects and the session end detected (SEDET bit in
OTG_FS_GOTGINT) interrupt is generated to notify that the OTG_FS has exited the
powered state.
In the powered state, the OTG_FS expects to receive some reset signaling from the host.
No other USB operation is possible. When a reset signaling is received the reset detected
interrupt (USBRST in OTG_FS_GINTSTS) is generated. When the reset signaling is
complete, the enumeration done interrupt (ENUMDNE bit in OTG_FS_GINTSTS) is
generated and the OTG_FS enters the Default state.
Soft disconnect
The powered state can be exited by software with the soft disconnect feature. The DP pull-
up resistor is removed by setting the soft disconnect bit in the device control register (SDIS
bit in OTG_FS_DCTL), causing a device disconnect detection interrupt on the host side
even though the USB cable was not really removed from the host port.
Default state
In the Default state the OTG_FS expects to receive a SET_ADDRESS command from the
host. No other USB operation is possible. When a valid SET_ADDRESS command is
decoded on the USB, the application writes the corresponding number into the device
address field in the device configuration register (DAD bit in OTG_FS_DCFG). The
OTG_FS then enters the address state and is ready to answer host transactions at the
configured USB address.
Suspended state
The OTG_FS peripheral constantly monitors the USB activity. After counting 3 ms of USB
idleness, the early suspend interrupt (ESUSP bit in OTG_FS_GINTSTS) is issued, and
confirmed 3 ms later, if appropriate, by the suspend interrupt (USBSUSP bit in
OTG_FS_GINTSTS). The device suspend bit is then automatically set in the device status
register (SUSPSTS bit in OTG_FS_DSTS) and the OTG_FS enters the suspended state.
The suspended state may optionally be exited by the device itself. In this case the
application sets the remote wakeup signaling bit in the device control register (RWUSIG bit
in OTG_FS_DCTL) and clears it after 1 to 15 ms.
When a resume signaling is detected from the host, the resume interrupt (WKUPINT bit in
OTG_FS_GINTSTS) is generated and the device suspend bit is automatically cleared.
To Next Page
Loading...
Need help?
General
