Intel 6 SERIES CHIPSET - DATASHEET 01-2011 Datasheet page 210

5.18.9.1.2 IN Transactions
An IN transaction receives data from the debug device. It can occur only when the
following are true:
• The debug port is enabled
• The debug software sets the GO_CNT bit
• The WRITE_READ#_CNT bit is reset
The sequence of the transaction is:
1. Software sets the appropriate values in the following bits:
— USB_ADDRESS_CNF
— USB_ENDPOINT_CNF
— TOKEN_PID_CNT[7:0]
— DATA_LEN_CNT
— WRITE_READ#_CNT: (note: this will always be 0 for IN transactions)
— GO_CNT: (note: this will always be 1 to initiate the transaction)
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.
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Functional Description
Datasheet