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PCI Express System Architecture by MindShare, Inc, Ravi Budruk, Don Anderson, Tom Shanley

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ACK/NAK Protocol Details

This section describes the detailed transmitter and receiver behavior in processing TLPs and ACK/NAK DLLPs. The examples demonstrate flow of TLPs from transmitter to the remote receiver in both the normal non-error case, as well as the error cases.

Transmitter Protocol Details

This section delves deeper into the ACK/NAK protocol. Consider the transmit side of a device's Data Link Layer shown in Figure 5-4 on page 215.

Sequence Number

Before a transmitter sends TLPs delivered by the Transaction Layer, the Data Link Layer appends a 12-bit Sequence Numbers to each TLP. The Sequence Number is generated by the 12-bit NEXT_TRANSMIT_SEQ counter. The counter is initialized to 0 at reset, or when the Data Link Layer is in the ...

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