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USB OTG Controller
Figure 58.
OMAP5912 OTG Controller HNP Events When Acting as a Default-B
Dual-Role OTG Device
D+ signaling by
default-A device
D+ from
OMAP5912
(acting as
default-B device)
Composite D+
Normal USB activity
Pulldown dominates D+
Pulldown dominates D+
A: OMAP5912 application decides that it wishes to communicate with the default-A device. System software
sets OTG_CTRL.B_BUSREQ.
B: Default-A device has no more traffic for the default-B device (OMAP5912). Default-A device suspends
the OTG link.
C: OMAP5912 OTG controller (acting as the OTG dual-role default-B device) sees OTG link suspended, sees
OTG_CTRL.B_HNPEN set to 1, sees OTG_CTRL.B_BUSREQ set to 1. OTG controller sets
OTG_CTRL.OTG_PU to 0 and issues OPRT_CHG interrupt.
D. OMAP5912 OTG interrupt handler sees OPRT_CHG interrupt and sees OTG_PU = 0. Handler initiates I
operation to disable OTG transceiver D+ pullup.
2
E. OMAP5912 I
C operations to disable the D+ pullup complete. OMAP5912 software sets
OTG_CTRL.OTG_PU to 1 to indicate that the D+ pullup disable operation has completed.
F. OMAP5912 OTG controller sees write of 1 to OTG_CTRL.OTG_PU and issues driver switch interupt.
G. OMAP5912 OTG interrupt handler sees driver switch interrupt, begins intialization of host port.
H. Default-A device sees SE0 on the OTG link, turns on its D+ pullup.
I. OMAP5912 OTG controller sees D+ pullup as HNP operation and OMAP5912 USB host contoller sees D+
pullup as an attach. OMAP5912 USB host controller signals USB reset, and enumerates the default-A
dual-role device as a peripheral, and begins normal USB bus activity.
J. Default-A device sees and responds appropriately to USB reset, enumeration and normal USB bus activity.
K. OMAP5912 application decides it has no more information to communicate to the default-A device. System
software suspends the USB host port which is being used for the OTG link, sets
OTG_CTRL.A_BUSREQ to 0.
L. OMAP5912 OTG controller sees OTG_CTRL.A_BUSREQ set to 0. OTG controller sets OTG_CTRL.OTG_PU
to 1 and issues both OPRT_CHG and driver switch interrupts.
M. Default-A device sees OTG link signal USB Suspend. Default-A device disables its D+ pullup.
N. OMAP5912 OTG interrupt handler sees OPRT_CHG interrupt, sees OTG_CTRL.OTG_PU set to 1, initiates
2
I
C operations to enable OTG transceiver D+ pullup.
O. OMAP5912 OTG interrupt handler sees Driver Switch and begins initialization of OMAP5912 USB device
controller.
2
P. OMAP5912 I
C operations to enable OTG transceiver D+ pullup complete.
Q. Default-A devcie sees D+ pullup, signals USB reset, issues Set Feature of the B_HNP_ENABLE feature,
and enumerates the OMAP5912 default-B dual-role device as a peripheral, and begins normal USB
bus activity.
R. OMAP5912 USB device controller sees and responds appropriately to USB reset, set feature of the
B_HNP_ENABLE feature, enumeration, and normal USB bus activity.
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Universal Serial Bus (USB)
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SPRU761A
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