307013-003 Datasheet, PDF (480/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

UHCI Controllers Registers
11.2.1
USBCMD—USB Command Register
I/O Offset:
Default Value:
Base + (00h–01h)
0000h
Attribute:
Size:
R/W
16 bits
The Command Register indicates the command to be executed by the serial bus host
controller. Writing to the register causes a command to be executed. The table
following the bit description provides additional information on the operation of the
Run/Stop and Debug bits.
Bit
Description
15:7
8
7
6
5
4
Reserved
Loop Back Test Mode — R/W.
0 = Disable loop back test mode.
1 = Intel^® ICH7 is in loop back test mode. When both ports are connected together, a
write to one port will be seen on the other port and the data will be stored in I/O
offset 18h.
Max Packet (MAXP) — R/W. This bit selects the maximum packet size that can be
used for full speed bandwidth reclamation at the end of a frame. This value is used by
the host controller to determine whether it should initiate another transaction based on
the time remaining in the SOF counter. Use of reclamation packets larger than the
programmed size will cause a Babble error if executed during the critical window at
frame end. The Babble error results in the offending endpoint being stalled. Software is
responsible for ensuring that any packet which could be executed under bandwidth
reclamation be within this size limit.
0 = 32 bytes
1 = 64 bytes
Configure Flag (CF) — R/W. This bit has no effect on the hardware. It is provided only
as a semaphore service for software.
0 = Indicates that software has not completed host controller configuration.
1 = HCD software sets this bit as the last action in its process of configuring the host
controller.
Software Debug (SWDBG) — R/W. The SWDBG bit must only be manipulated when
the controller is in the stopped state. This can be determined by checking the HCHalted
bit in the USBSTS register.
0 = Normal Mode.
1 = Debug mode. In SW Debug mode, the host controller clears the Run/Stop bit after
the completion of each USB transaction. The next transaction is executed when
software sets the Run/Stop bit back to 1.
Force Global Resume (FGR) — R/W.
0 = Software resets this bit to 0 after 20 ms has elapsed to stop sending the Global
Resume signal. At that time all USB devices should be ready for bus activity. The 1
to 0 transition causes the port to send a low speed EOP signal. This bit will remain
a 1 until the EOP has completed.
1 = Host controller sends the Global Resume signal on the USB, and sets this bit to 1
when a resume event (connect, disconnect, or K-state) is detected while in global
suspend mode.
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Intel ^® ICH7 Family Datasheet