Datasheet 677
EHCI Controller Registers (D29:F0, D26:F0)
6
Force Port Resume — R/W.
0 = No resume (K-state) detected/driven on port. (Default)
1 = Resume detected/driven on port. 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 1 because a
J-to-K transition is detected, the Port Change Detect bit (D29:F0,
D26:F0:CAPLENGTH + 24h, bit 2) in the USB2.0_STS register is also set to a 1. If
software sets this bit to a 1, the host controller must not set the Port Change Detect
bit.
NOTE: 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 1. Software must appropriately time the Resume and set this bit to a 0 when
the appropriate amount of time has elapsed. Writing a 0 (from 1) 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 1 until the port has switched to the high-speed idle.
5
Overcurrent Change — R/WC. The functionality of this bit is not dependent upon the
port owner. Software clears this bit by writing a 1 to it.
0 = No change. (Default)
1 = There is a change to Overcurrent Active.
4
Overcurrent Active — RO.
0 = This port does not have an overcurrent condition. (Default)
1 = This port currently has an overcurrent condition. This bit will automatically
transition from 1 to 0 when the over current condition is removed. The PCH
automatically disables the port when the overcurrent active bit is 1.
3
Port Enable/Disable Change — R/WC. For the root hub, this bit gets set to a 1 only
when a port is disabled due to the appropriate conditions existing at the EOF2 point (See
Chapter 11 of the USB Specification for the definition of a port error). This bit is not set
due to the Disabled-to-Enabled transition, nor due to a disconnect. Software clears this
bit by writing a 1 to it.
0 = No change in status. (Default).
1 = Port enabled/disabled status has changed.
2
Port Enabled/Disabled — R/W. Ports can only be enabled by the host controller as a
part of the reset and enable. Software cannot enable a port by writing a 1 to this bit.
Ports can be disabled by either a fault condition (disconnect event or other fault
condition) or by host software. Note that the bit status does not change until the port
state actually changes. There may be a delay in disabling or enabling a port due to other
host controller and bus events.
0 = Disable
1 = Enable (Default)
1
Connect Status Change — R/WC. This bit indicates a change has occurred in the port’s
Current Connect Status. Software sets this bit to 0 by writing a 1 to it.
0 = No change (Default).
1 = Change in Current Connect Status. The host controller sets this bit for all changes to
the port device connect status, even if system software has not cleared an existing
connect status change. For example, the insertion status changes twice before
system software has cleared the changed condition, hub hardware will be “setting”
an already-set bit (that is, the bit will remain set).
0
Current Connect Status — RO. This value reflects the current state of the port, and
may not correspond directly to the event that caused the Connect Status Change bit (Bit
1) to be set.
0 = No device is present. (Default)
1 = Device is present on port.
Bit Description
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