ST STM32L4 5 Series Reference Manual page 1629

RM0351
1. Use a regulator to build a bus-powered device.
47.6.1 SRP-capable peripheral
The SRP capable bit in the Global USB configuration register (SRPCAP bit in
OTG_GUSBCFG) enables the OTG_FS to support the session request protocol (SRP). In
this way, it allows the remote A-device to save power by switching off V
session is suspended.
The SRP peripheral mode program model is described in detail in the
request protocol
47.6.2 Peripheral states
Powered state
The V
BUS
to enter the powered state (see USB2.0 section 9.1). 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_GINTSTS) to notify the
powered state.
The V
BUS
operations. If a drop in V
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_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_GINTSTS) is generated. When the reset signaling is complete,
the enumeration done interrupt (ENUMDNE bit in OTG_GINTSTS) is generated and the
OTG_FS enters the Default state.
Figure 519. USB_FS peripheral-only connection
section.
input detects the B-Session valid voltage by which the USB peripheral is allowed
input also ensures that valid V
below B-session valid happens to be detected (for instance
BUS
DocID024597 Rev 5
USB on-the-go full-speed (OTG_FS)
levels are supplied by the host during USB
BUS
while the USB
BUS
B-device session
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