82801DB Datasheet, PDF (208/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
2. The debug port controller sends a token packet consisting of:
— SYNC
— TOKEN_PID_CNT field
— USB_ADDRESS_CNT field
— USB_ENDPOINT_CNT field
— 5-bit CRC field.
3. After sending the token packet, the debug port controller waits for a response from the debug
device.
If a response is received:
— The received PID is placed into the RECEIVED_PID_STS field
— Any subsequent bytes are placed into the DATA_BUFFER
— The DATA_LEN_CNT field is updated to show the number of bytes that were received
after the PID.
4. If valid packet was received from the device that was one byte in length (indicating it was a
handshake packet), then the debug port controller:
— Resets the ERROR_GOOD#_STS bit
— Sets the DONE_STS bit
5. If valid packet was received from the device that was more than one byte in length (indicating
it was a data packet), then the debug port controller:
— Transmits an ACK handshake packet
— Resets the ERROR_GOOD#_STS bit
— Sets the DONE_STS bit
6. If no valid packet is received, then the debug port controller:
— Sets the EXCEPTION_STS field to 001b
— Sets the ERROR_GOOD#_STS bit
— Sets the DONE_STS bit.
5.17.10.1.3 Debug Software
Enabling the Debug Port
There are two mutually exclusive conditions that debug software must address as part of its startup
processing:
• The EHCI has been initialized by system software
• The EHCI has not been initialized by system software
Debug software can determine the current “initialized” state of the EHCI by examining the
Configure Flag in the EHCI USB 2.0 Command Register. If this flag is set, then system software
has initialized the EHCI. Otherwise, the EHCI should not be considered initialized. Debug
software will initialize the debug port registers depending on the state the EHCI. However, before
this can be accomplished, debug software must determine which root USB port is designated as the
debug port.
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Intel^® 82801DB ICH4 Datasheet