DocID018909 Rev 11
RM0090
USB on-the-go full-speed (OTG_FS)
1368
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.
Figure 406. A-device SRP
1. DRV_VBUS = V
BUS
drive signal to the PHY
VBUS_VALID = V
BUS
valid signal from PHY
A_VALID = A-peripheral V
BUS
level signal to PHY
D+ = Data plus line
D- = Data minus line
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
BUS
power is off.
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
BUS
above the A-device session valid (2.0 V minimum) for V
BUS
pulsing.
The OTG_FS controller interrupts the application on detecting SRP. The Session
request detected bit is set in Global interrupt status register (SRQINT set in
OTG_FS_GINTSTS).
6. The application must service the Session request detected interrupt and turn on the
port power bit by writing the port power bit in the host port control and status register.
The PHY indicates port power-on by asserting the VBUS_VALID signal.
7. When the USB is powered, the device connects, completing the SRP process.
ai15681
DRV_VBUS
VBUS_VALID
A_VALID
D+
D-
Suspend
V
BUS
pulsing
Data line pulsing
Connect
1
6
2
5
3
4
7
Low
