Application Layer may need to track credits consumed and use the credit limit information to calculate the number of credits available. The number of credits available is calculated by the credit limit minus credits consumed.
Since "tx_cred_fchipcons" is asserted for 1 cycle each time the Hard IP consumes a credit, Application Layer user logic may capture the signal and reflect it to internal counter to be aware of credits consumed.
The credit limit is the sum of all credits issued by the receiver. It's initialized during the flow control initialization phase of link initialization and then updated during operation by Flow Control (FC) Update DLLPs.
Prior to PCIe® Hard IP of Stratix® V devices, the TX datapath provides a TX credit (tx_cred) vector which reflects the number of credits available. But TX credit interfaces was changed since PCIe Hard IP of Stratix V devices, and it provides "credits limit" and "credits consumed" information on "tx_cred_datafc*", "tx_cred_hdrfc*" and "tx_credfchipcons" interfaces for posted headers, posted data, non-posted headers, non-posted data, completion headers and completion data, instead of the number of credits available.