PCI Express System Architecture

Error Situations Reliably Handled by ACK/NAK Protocol

This section describes the possible sources of errors that may occur in delivery of TLPs from a transmitter to a receiver across a Link. The ACK/NAK protocol guarantees reliable delivery of TLPs despite the unlikely event that these errors occur. Below is a bullet list of errors and the related error correction mechanism the protocol uses to resolve the error:

• Problem: CRC error occurs in transmission of a TLP (see “Transmitter's Response to a NAK DLLP” on page 224 and “Receiver Schedules a NAK” on page 233.)

  Solution: Receiver detects LCRC error and schedules a NAK DLLP with Sequence Number = NEXT_RCV_SEQ count - 1. Transmitter replays TLPs.

• Problem: One or more TLPs are lost en route to ...