Teledyne LeCroy Conquest User Manual - Users Manual - Manual (Page 164)

OTG Exerciser (Optional)
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Session Request Protocol (SRP)
To conserve power, the OTG supplement allows an A-device to leave VBUS
turned off when the bus is not being used. If the B-device wants to use the bus
when VBUS is turned off, the B-device can use the OTG-supplement
Session Request Protocol (SRP) to request the A-device to supply power on
the VBUS.
The SRP has two methods that the B-device uses to request that the A-device
begins a session: data-line pulsing and VBUS pulsing. The two signaling
methods allow maximum latitude in the design of A-devices. An A-device is
only required to respond to one of the two SRP signaling methods. When
initiating SRP, a B-device must use both methods, to insure that the A-device
responds. Any A-device, including a PC or laptop, can respond to SRP.
Any B-device, including a standard USB peripheral, can initiate SRP.
Dual-role devices can initiate and respond to SRP.
A session is the time period that VBUS is above the Session Valid threshold
of a device. The A-device threshold is within the range defined by
VA_SESS_VLD, and the B-device threshold is within the range defined by
VB_SESS_VLD, as shown in the following table.
When a session starts, the A-device defaults to the role of Host. During a
session, the Host Negotiation Protocol (see preceding section) can transfer
the role of Host back and forth between the A-device and the B-device any
number of times. The session ends when VBUS falls below the A-device
Session Valid threshold.
How to Turn Off the VBUS (in an OTG Script)
To turn off the VBus, click the Drop Session button in the OTG Exerciser GUI.
How Long Does Conquest Take to Drop D+ Pull-up?
After detecting the sequence Chirp K-J-K-J-K-J, the USB Analyzer
disconnects the D+ pull-up resistor in 500 microseconds.