Altera POS-PHY Level 4 IP Core - Manual (Page 54)

4–16 Chapter 4: Functional Description—Receiver
Error Flagging and Handling
POS-PHY Level 4 IP Core User Guide December 2014 Altera Corporation
After the optional channel aligner, the training pattern is treated as IDLEs and
discarded. The training pattern has no internal function because the data entering the
IP core is already byte aligned.
A status flag, stat_rd_tp_flag, is also provided. This flag pulses high for one clock
cycle at the end of the training pattern to indicate that a correct training pattern has
been detected. This flag pulses once for every occurrence of 10 (repeated) training
control words followed by 10 (repeated) training data words. This flag does not
indicate that the data path has been deskewed.
DIP-4 Marking
The receiver IP core supports three different ways of handling DIP-4 errors. In the first
mode, the none mode, the err_rd_dip4 signal is asserted but no packets are marked
as errored. You should use a higher level CRC or FCS to detect packets with errors. In
the second mode, the optimistic mode, the IP core only marks packets that have a high
probability of having errors. In the third mode, the pessimistic mode, the IP core
assumes the worst case and marks any packet that may have errors. In all modes, if
the IP core detects a DIP-4 error, it asserts the err_rd_dip4 signal.
The optimistic and pessimistic modes are discussed further in these sub-sections,
where an open packet is a packet for which a SOP but not an EOP has been received
when the error was detected.
Optimistic Mode
This mode attempts to error individual bursts as opposed to entire packets. Any data
burst incoming on the SPI-4.2 interface is marked with an Atlantic error if its starting
payload control word contains a DIP-4 error, or its terminating control word contains
a DIP-4 error.
If the starting payload control word contains a DIP-4 error, the aN_arxerr signal is
asserted for as long as the burst is present on the Atlantic interface. If the terminating
control word contains a DIP-4 error, the aN_arxerr signal is asserted on the last
Atlantic data cycle of the burst.
The IP core does not keep track of open packets containing errors that have not been
terminated with an EOP. The Atlantic error signal is not held until EOP and it is up to
the user logic to ensure that errors are carried across continued packets if required.
1 In cases where the terminating control word contains an EOP, the associated
aN_arxmty
value is not rounded down to the nearest even value.
Pessimistic Mode
In the event of a DIP-4 error, all open packets are marked. All subsequent data for
each port is marked until a new SOP for that port is received.
1
Because of the logic required to track open packets per ports, this feature uses a large
amount of logic for systems with many ports.