NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 740 -
Revision V1.30
NUC97
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CHNIC
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[7]
SUSPEND
Suspend (R/W)
Port Enabled Bit and Suspend bit of this register define the port states as follows:.
00 = Disable.
01 = Disable.
10 = Enable.
11 = Suspend.
When in suspend state, downstream propagation of data is blocked on this port, except for
port reset. The blocking occurs at the end of the current transaction, if a transaction was in
progress when this bit was written to 1. In the suspend state, the port is sensitive to
resume detection. Note that the bit status does not change until the port is suspended and
that there may be a delay in suspending a port if there is a transaction currently in progress
on the USB.
A write of zero to this bit is ignored by the host controller. The host controller will
unconditionally set this bit to a zero when:
Software sets the Force Port Resume bit to a zero (from a one).
Software sets the Port Reset bit to a one (from a zero).
If host software sets this bit to a one when the port is not enabled (i.e.
Port enabled bit is a zero) the results are undefined.
This field is zero if Port Power is zero.
0 = Port not in suspend state.
1 = Port in suspend state.
[6]
FPR
Force Port Resume (R/W)
This functionality defined for manipulating this bit depends on the value of the Suspend bit.
For example, if the port is not suspended (Suspend and Enabled bits are a one) and
software transitions this bit to a one, then the effects on the bus are undefined.
Software sets this bit to a 1 to drive resume signaling. The Host Controller sets this bit to a
1 if a J-to-K transition is detected while the port is in the Suspend state. When this bit
transitions to a one because a J-to-K transition is detected, the Port Change Detect bit in
the USBSTS register is also set to a one. If software sets this bit to a one, the host
controller must not set the Port Change Detect bit.
Note that when the EHCI controller owns the port, the resume sequence follows the
defined sequence documented in the USB Specification Revision 2.0. The resume
signaling (Full-speed 'K') is driven on the port as long as this bit remains a one. Software
must appropriately time the Resume and set this bit to a zero when the appropriate amount
of time has elapsed. Writing a zero (from one) causes the port to return to high-speed
mode (forcing the bus below the port into a high-speed idle). This bit will remain a one until
the port has switched to the high-speed idle. The host controller must complete this
transition within 2 milliseconds of software setting this bit to a zero.
This field is zero if Port Power is zero.
0 = No resume (Kstate) detected/driven on port.
1 = Resume detected/driven on port.
[5]
OCC
Over-current Change (R/WC)
1 = This bit gets set to a one when there is a change to Over-current Active. Software
clears this bit by writing a one to this bit position.
[4]
OCA
Over-current Active (RO)
This bit will automatically transition from a one to a zero when the over current condition is
removed.
0 = This port does not have an over-current condition.
1 = This port currently has an overcurrent condition.