Texas Instruments OMAP5912 Reference Manual page 1532

USB OTG Controller
Figure 57. OMAP5912 OTG Controller HNP Events When Acting as a Default-A
Dual-Role OTG Device
D+ from
OMAP5912
(acting as default-A
device)
D+ Signaling by
default-B device
Composite D+
Normal USB activity
Pulldown dominates D+
Pulldown dominates D+
A: OMAP5912 application has no more traffic for default-B device. System software suspends
the USB host port which is being used for the OTG link, sets OTG_CTRL.A_BUSREQ to 0.
If the OTG transceiver supports the autoconnect feature, system software should initiate
the appropriate I
B: Default-B device sees OTG link suspended by default-A device. Because the default-B device
is enabled for HNP, and desires to issue HNP, it disables its D+ pullup, allowing D+ to
float. Default-B controller waits for OMAP5912 to enable its D+ pullup.
C: OMAP5912 OTG controller sees OTG_CTRL.A_SETB_HNPEN=1 and sees SE0 on the bus.
OTG controller sets OTG_CTRL.OTG_PU to 0 and issues both the OPRT_CHG interrupt
and the driver switch interrupt.
C1. If the OTG transceiver autoconnect feature was enabled in step A, the OTG transceiver will
automatically enable its D+ pullup upon seeing SE0 on the bus, and issue an interrupt.
C2.OMAP5912 GPIO interrupt handler sees an OTG transceiver interrupt and issues I
operations to query the transceiver interrupt source.
C3. OMAP5912 I
It is not necessary to update any OTG controller registers when auto-HNP occurs.
D. OMAP5912 OTG interrupt handler sees OPRT_CHG interrupt and OTG_PU set to 1, and (if
auto-HNP is not used) causes I
OMAP5912 OTG interrupt handler sees driver switch interrupt and begins initialization of
USB device controller.
E. Default-B device sees D+ pullup as HNP operation and begins acting as a USB host. It
signals USB reset and enumerates the OMAP5912 dual-role device as a peripheral, and
begins normal USB bus activity.
F. OMAP5912 USB device controller sees and responds appropriately to USB reset, enumeration
and normal USB bus activity.
G. Default-B device finishes its bus activity and suspends the USB link.
H. OMAP5912 application decides that it wants to communicate with the default-B device. System
software sets OTG_CTRL.A_BUSREQ.
I. OMAP5912 OTG controller sees suspend signaled on the OTG link, sets OTG_CTRL.OTG_PU
to 0, issues OPRT_CHG interrupt.
J. OMAP5912 OTG interrupt handler sees OPRT_CHG interrupt, sees OTG_CTRL.OTG_PU set to
0, issues I
K. OMAP5912 I
OTG_CTRL.OTG_PU to 1 to indicate that the D+ pullup disable operation has completed.
L. OMAP5912 OTG controller sees write of 1 to OTG_CTRL.OTG_PU and issues driver switch
interupt.
M. OMAP5912 OTG interrupt handler sees driver switch interrupt, begins intialization of host port.
N. Default-B device sees SE0 on the OTG link, turns on its D+ pullup.
O. OMAP5912 OTG controller and USB host controller see D+ pullup as HNP operation.
OMAP5912 USB host controller signals USB reset, sends the set feature signal with B_HNPEN
feature enabled, and enumerates the default-B dual-role device as a peripheral, and
begins normal USB bus activity.
P. Default-B device sees and responds appropriately to USB reset, the set feature signal, enumeration and
normal USB bus activity.
240 Universal Serial Bus (USB)
(optional)
C1C2C3
A
D
B
E
C
2
C operations to enable it before suspending the OTG link.
2
C operation completes and the interrupt status shows autoconnect occurred.
C operation to enable OTG transceiver D+ pullup.
2
2
C operations to disable the OTG transceiver D+ pullup.
2
C operations to disable the D+ pullup complete. OMAP5912 software sets
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L M
H
J
O
G I
N
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