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USB Controller Registers (D31:F2)
10-14
82801AA and 82801AB Datasheet
10.2.7
PORTSC[0,1]—Port Status and Control Register
I/O Offset:
Port 0: Base + (10–11h)
Port 1: Base + (12–13h)
0080h
Attribute:
R/W (Writes must be a Word write
Default Value:
Size:
16 bits
After a Power-up reset, Global reset, or Host Controller reset, the initial conditions of a port are: no
device connected, Port disabled, and the bus line status is 00 (single-ended zero).
Bit
Description
15:13
Reserved— RO.
12
Suspend
— R/W
.
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 State
x,0
Disable
0,1
Enable
1,1
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.
1 = Port in suspend state.
0 = Port not in suspend state.
Note: Suspending a port is supposed to stop when the current transaction completes. However, if
there is a specific error condition, the ICH may issue a start-of-frame, and then shut down.
11
Overcurrent Indicator
— R/WC. Set by hardware
1 = Overcurrent pin has gone from inactive to active on this port.
0 = This bit is cleared by software writing a ‘1’.
10
Overcurrent Active
— RO.
1 = Set by hardware to indicate that the overcurrent pin is active (low).
0 = Cleared by hardware to indicate that the overcurrent pin is inactive (high).
9
Port Reset
— RO
.
When set, the port is disabled and sends the USB Reset signaling.
8
Low Speed Device Attached (LS)
— RO
.
Writes have no effect.
1 = Low speed device is attached to this port.
0 = Full speed device is attached.
7
Reserved— RO: Always read as 1.
6
Resume Detect (RSM_DET)
— R/W. 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 for at least 32 microseconds while
the port is in the Suspend state. The ICH will then reflect the K-state back onto the bus as long as
the bit remains a ‘1’, and the port is still in the suspend state (bit 12,2 are ‘11’). 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.
1 = Resume detected/driven on port.
0 = No resume (K-state) detected/driven on port.
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.
3
Port Enable/Disable Change
— RW
.
For the root hub, this bit gets set only when a port is disabled
due to disconnect on 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.
1 = Port enabled/disabled status has changed.
0 = No change.