82801FB Datasheet, PDF (209/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

Functional Description
The Debug port facilitates operating system and device driver debug. It allows the software to
communicate with an external console using a USB 2.0 connection. Because the interface to this
link does not go through the normal USB 2.0 stack, it allows communication with the external
console during cases where the operating system is not loaded, the USB 2.0 software is broken, or
where the USB 2.0 software is being debugged. Specific features of this implementation of a debug
port are:
• Only works with an external USB 2.0 debug device (console)
• Implemented for a specific port on the host controller
• Operational anytime the port is not suspended AND the host controller is in D0 power state.
• Capability is interrupted when port is driving USB RESET
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.
Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet
209