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 a 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 a 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.
5.19.10.1.3 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 of the EHCI. However, before this can be accomplished, debug software must
determine which root USB port is designated as the debug port.
Determining the Debug Port
Debug software can easily determine which USB root port has been designated as the
debug port by examining bits 20:23 of the EHCI Host Controller Structural Parameters
register. This 4-bit field represents the numeric value assigned to the debug port
(i.e., 0000 = port 0).
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Datasheet
INTEL [ INTEL ]
