RM0090: Reference manual - STMicroelectronics

USB on-the-go high-speed (OTG_HS) RM0090
A-device session request protocol
The application must set the SRP-capable bit in the Core USB configuration register. This
enables the OTG_HS controller to detect SRP as an A-device.
Figure 398. A-device SRP
DRV_VBUS
VBUS_VALID
A_VALID
OTG_HS_FS_DP
OTG_HS_FS_DM
Suspend
Low
1. DRV_VBUS = VBUS drive signal to the PHY
VBUS_VALID = VBUS valid signal from PHY
A_VALID = A-device VBUS level signal to PHY
DP = Data plus line
DM = 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 VBUS power is off.
4. To initiate SRP, the device turns on its data line pull-up resistor for 5 to 10 ms. The
OTG_HS controller detects data-line pulsing.
5. The device drives VBUS above the A-device session valid (2.0 V minimum) for VBUS pulsing.
The OTG_HS controller interrupts the application on detecting SRP. The Session
request detected bit is set in Global interrupt status register (SRQINT set in
OTG_HS_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.
1307/1416 Doc ID 018909 Rev 3
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V BUS pulsing
4 7
Data line pulsing
Connect
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