Universal Serial Bus (USB) Configuration

Bit

Description

 

 

12

Suspend–R/W.1=Port in suspend state. 0=Port not in suspend state. This bit should not be

 

written to a 1 if global suspend is active (bit 3=1 in the USBCMD register). Bit 2 and bit 12 of this

 

register define the hub states as follows:

 

Bits [12,2] Hub Port State

 

x0 Disable

 

01 Enable

 

11 Suspend

 

When in suspend state, downstream propagation of data is blocked on this port, except for single-

 

ended 0 resets (global reset and 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.

 

 

11

Over-current Indicator Change–R/WC.1=A change from 1 to 0 has been detected on the Over-

 

current (OC[X]#) pin for this port. 0=No change has been detected. Software sets this bit to 0 by

 

writing a 1 to it.

 

 

10

Over-currentIndicator–RO.1=Overcurrent pin (OC[X]#) for this port is at logic 0 indicating over-

 

current condition. 0=Overcurrent pin for this port is at logic 1 indicating a normal condition. If

 

asserted, the corresponding port is disabled.

 

 

9

Port Reset–R/W. 1=Port is in Reset. 0=Port is not in Reset. When in the Reset State, the port is

 

disabled and sends the USB Reset signaling. Note that host software must ensure that the

 

RESET signaling is active for the proper amount of time as specified in the USB Specification.

 

 

8

Low Speed Device Attached–RO.1=Low speed device is attached to this port. 0=Full speed

 

device. Writes have no effect.

 

 

7

Reserved–RO.Always read as 1.

 

 

6

Resume Detect–R/W.1= Resume detected/driven on port. 0=No resume (K-state) 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. Note that when this

 

bit is 1, a K-state is driven on the port as long as this bit remains 1 and the port is still in suspend

 

state. Writing a 0 (from 1) causes the port to send a low speed EOP. This bit will remain a 1 until

 

the EOP has completed.

 

 

5:4

Line Status–RO.These bits reflect the D+ (bit 4) and D- (bit 5) signals lines’ logical levels. These

 

bits are used for fault detect and recovery as well as for USB diagnostics. This field is updated at

 

EOF2 time (See Chapter 11 of the USB Specification).

 

 

3

Port Enable/Disable Change–R/WC.1=Port enabled/disabled status has changed. 0=No

 

change. For the root hub, this bit gets set only when a port is disabled due to disconnect on the

 

that port or due to the appropriate conditions existing at the EOF2 point (See Chapter 11 of the

 

USB Specification). Software clears this bit by writing a 1 to it.

 

 

2

Port Enabled/Disabled–R/W.1=Enable. 0=Disable. Ports can be enabled by host software only.

 

Ports can be disabled by either a fault condition (disconnect event, overcurrent condition, or other

 

fault condition) or by host software. Note that the bit status does not change until the port state

 

actually changes and that there may be a delay in disabling or enabling a port if there is a

 

transaction currently in progress on the USB.

 

 

1

Connect Status Change–R/WC.1=Change in Current Connect Status. 0=No change.

 

Indicates a change has occurred in the port’s Current Connect Status (see bit 0). The hub device

 

sets this bit for any changes to the port device connect status, even if system software has not

 

cleared a connect status change. If, for example, the insertion status changes twice before system

 

software has cleared the changed condition, hub hardware will be “setting” an already-set bit (i.e.

 

the bit will remain set). However, the hub transfers the change bit only once when the Host

 

Controller requests a data transfer to the Status Change endpoint. System software is responsible

 

for determining state change history in such a case. Software sets this bit to 0 by writing a 1 to it.

 

 

0

Current Connect Status–RO.1=Device is present on port. 0=No device is present. 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.

 

 

Intel® 460GX Chipset Software Developer’s Manual

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