307013-003 Datasheet, PDF (215/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
5.20.10.1 Theory of Operation
There are two operational modes for the USB debug port:
1. Mode 1 is when the USB port is in a disabled state from the viewpoint of a standard
host controller driver. In Mode 1, the Debug Port controller is required to generate a
“keepalive” packets less than 2 ms apart to keep the attached debug device from
suspending. The keepalive packet should be a standalone 32-bit SYNC field.
2. Mode 2 is when the host controller is running (i.e., host controller’s Run/Stop# bit
is 1). In Mode 2, the normal transmission of SOF packets will keep the debug
device from suspending.
Behavioral Rules
1. In both modes 1 and 2, the Debug Port controller must check for software
requested debug transactions at least every 125 microseconds.
2. If the debug port is enabled by the debug driver, and the standard host controller
driver resets the USB port, USB debug transactions are held off for the duration of
the reset and until after the first SOF is sent.
3. If the standard host controller driver suspends the USB port, then USB debug
transactions are held off for the duration of the suspend/resume sequence and until
after the first SOF is sent.
4. The ENABLED_CNT bit in the debug register space is independent of the similar
port control bit in the associated Port Status and Control register.
Table 5-49 shows the debug port behavior related to the state of bits in the debug
registers as well as bits in the associated Port Status and Control register.
Table 5-49. Debug Port Behavior (Sheet 1 of 2)
OWNER_CNT ENABLED_CT
Port
Enable
Run /
Stop
Suspend
Debug Port Behavior
0
X
X
X
X
Debug port is not being used.
Normal operation.
1
0
X
X
X
Debug port is not being used.
Normal operation.
Debug port in Mode 1. SYNC
1
1
0
0
X
keepalives sent plus debug
traffic
Debug port in Mode 2. SOF
(and only SOF) is sent as
keepalive. Debug traffic is
1
1
0
1
X
also sent. Note that no other
normal traffic is sent out this
port, because the port is not
enabled.
Invalid. Host controller driver
1
1
1
0
0
should not put the controller
into this state (enabled, not
running and not suspended).
Intel ^® ICH7 Family Datasheet
215