Altera POS-PHY Level 4 IP Core Manual do Utilizador descarregar pdf (Página 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

IDLE

s 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.

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