Otg Programming Model - ST STM32F413 Reference Manual

USB on-the-go full-speed (OTG_FS)
33.16.7

OTG programming model

The OTG_FS controller is an OTG device supporting HNP and SRP. When the core is
connected to an "A" plug, it is referred to as an A-device. When the core is connected to a
"B" plug it is referred to as a B-device. In host mode, the OTG_FS controller turns off V
to conserve power. SRP is a method by which the B-device signals the A-device to turn on
V power. A device must perform both data-line pulsing and V
BUS
detect either data-line pulsing or V
device negotiates and switches to host role. In Negotiated mode after HNP, the B-device
suspends the bus and reverts to the device role.
A-device session request protocol
The application must set the SRP-capable bit in the Core USB configuration register. This
enables the OTG_FS controller to detect SRP as an A-device.
1. DRV_VBUS = V
VBUS_VALID = V
A_VALID = A-peripheral V
D+ = Data plus line
D- = Data minus line
The following points refer and describe the signal numeration shown in the
1. To save power, the application suspends and turns off port power when the bus is idle
by writing the port suspend and port power bits in the host port control and status
register.
2. PHY indicates port power off by deasserting the VBUS_VALID signal.
3. The device must detect SE0 for at least 2 ms to start SRP when V
4. To initiate SRP, the device turns on its data line pull-up resistor for 5 to 10 ms. The
OTG_FS controller detects data-line pulsing.
5. The device drives V
pulsing.
The OTG_FS controller interrupts the application on detecting SRP. The Session
1240/1284
BUS
Figure 401. A-device SRP
drive signal to the PHY
BUS
valid signal from PHY
BUS
level signal to PHY
BUS
above the A-device session valid (2.0 V minimum) for V
BUS
DocID029473 Rev 3
pulsing for SRP. HNP is a method by which the B-
RM0430
pulsing, but a host can
BUS
Figure 401:
power is off.
BUS
BUS
BUS