82801DB Datasheet, PDF (445/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

EHCI Controller Registers (D29:F7)
Bit
15:14
13
12
11:10
9
Description
Reserved — RW. Should be written to =00b.
Port Owner — RW. Default = 1b. This bit unconditionally goes to a 0 when the Configured Flag bit in
the CONFIGFLAG register makes a 0-to-1 transition.
System software uses this field to release ownership of the port to a selected host controller (in the
event that the attached device is not a high-speed device). Software writes a 1 to this bit when the
attached device is not a high-speed device. A 1 in this bit means that a companion host controller
owns and controls the port. For operational details, see Chapter 4 of the Enhanced Host Controller
Interface (EHCI) Specification for Universal Serial Bus.
Port Power (PP)  RO. Hardwired to 1. This indicates that the port does have power.
Line Status— RO.These bits reflect the current logical levels of the D+ (bit 11) and D- (bit 10) signal
lines. These bits are used for detection of low-speed USB devices prior to the port reset and enable
sequence. This field is valid only when the port enable bit is 0 and the current connect status bit is
set to a 1.
00 = SE0
10 = J-state
01 = K-state
11 = Undefined
Reserved. This bit will return a 0 when read.
Port Reset — RW. When software writes a 1 to this bit (from a 0), the bus reset sequence as
defined in the Universal Serial Bus (USB) Specification, Revision 2.0 is started. Software writes a 0
to this bit to terminate the bus reset sequence. Software must keep this bit at a 1 long enough to
ensure the reset sequence completes, as specified in the Universal Serial Bus (USB) Specification,
Revision 2.0.
0 = Port is not in Reset. (Default)
1 = Port is in Reset.
NOTE: When software writes this bit to a 1, it must also write a 0 to the Port Enable bit. When
software writes a 0 to this bit, there may be a delay before the bit status changes to a 0. The
8
bit status will not read as a 0 until after the reset has completed. If the port is in high-speed
mode after reset is complete, the host controller will automatically enable this port (e.g., set
the Port Enable bit to a 1). A host controller must terminate the reset and stabilize the state
of the port within 2 milliseconds of software transitioning this bit from 1 to 0.
For example: if the port detects that the attached device is high-speed during reset, then the
host controller must have the port in the enabled state within 2 ms of software writing this bit
to a 0. The HCHalted bit in the EHCI_STS register should be a 0 before software attempts
to use this bit. The host controller may hold Port Reset asserted to a 1 when the HCHalted
bit is a 1. This field is 0 if Port Power is 0.
Warning: System software should not attempt to reset a port if the HCHalted bit in the EHCI_STS
register is a 1. Doing so will result in undefined behavior.
Suspend — RW.
0 = Port not in suspend state. (Default).
1 = Port in suspend state.
Port Enabled Bit and Suspend bit of this register define the port states as follows:
Bits [Port Enabled, Suspend]
Port State
0X
Disable
10
7
11
Enable
Suspend
• When in suspend state, downstream propagation of data is blocked on this port, except for port
reset. Note that the bit status does not change until the port is suspended and that there may be
a delay in suspending a port depending on the activity on the port.
• The host controller will unconditionally set this bit to a 0 when software sets the Force Port
Resume bit to a 0 (from a 1). A write of 0 to this bit is ignored by the host controller.
• If host software sets this bit to a 1 when the port is not enabled (i.e., Port enabled bit is a 0) the
results are undefined.
Intel^® 82801DB ICH4 Datasheet
445