AMD SB600 Technical Reference Manual page 89

PORTSC (1-N_PORTS) –RW - 32 bits - [EOR_Reg : EHCI_EOR + (44h~68h)]
Field Name Bits
Port Reset 8
Reserved 9
Line Status 11:10
Port Power 12
©2008 Advanced Micro Devices, Inc.
AMD SB600 Register Reference Manual
Default
0b 1 = Port is in Reset.
0 = Port is not in Reset.
When software writes a one to this bit (from a zero), the bus reset
sequence as defined in the USB Specification Revision 2.0 is started.
Software writes a zero to this bit to terminate the bus reset sequence.
Software must keep this bit at a one long enough to ensure the reset
sequence, as specified in the USB Specification Revision 2.0, completes.
Note: when software writes this bit to a one, it must also write a zero to
the Port Enable bit.
Note that when software writes a zero to this bit there may be a delay
before the bit status changes to a zero. The bit status will not read as a
zero 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 one). A host controller must
terminate the reset and stabilize the state of the port within 2 milliseconds
of software transitioning this bit from a one to a zero. 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 2ms of
software writing this bit to a zero.
The HCHalted bit in the USBSTS register should be a zero before
software attempts to use this bit. The host controller may hold Port Reset
asserted to a one when the
HCHalted bit is a one. This field is zero if Port Power is zero.
This bit is reserved for future use, and should return a value of zero when
read.
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 zero and the current connect status bit is
set to a one.
The encoding of the bits are:
Bits[11:10] USB State Interpretation
00b SE0
10b J-state
01b K-state
11b Undefined Not Low-speed device, perform EHCI reset.
This value of this field is undefined if Port Power is zero.
[Read-only]
The function of this bit depends on the value of the Port Power Control
(PPC) field in the HCSPARAMS register. The behavior is as follows:
PPC PP Operation
0b 1b RO -    H ost controller does not have port power control
switches. Each port is hard-wired to power.
1b 1b/0b RW - Host controller has port power control switches.
This bit represents the current setting of the switch (0 = off, 1 = on). When
power is not available on a port (i.e.
PP equals a 0), the port is non-functional and will not report attaches,
detaches, etc.
When an over-current condition is detected on a powered port and PPC is
a one, the PP bit in each affected port may be transitioned by the host
controller from a 1 to 0 (removing power from the port).
[Read-write or Read-only]
Description
Not Low-speed device, perform EHCI reset
Not Low-speed device, perform EHCI reset
Low-speed device, release ownership of port
OCHI USB 1.1 and EHCI USB 2.0 Controllers
Proprietary Page 89