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4–20 Chapter 4: Functional Description—Receiver

Error Flagging and Handling

POS-PHY Level 4 IP Core User Guide December 2014 Altera Corporation

The Atlantic FIFO buffer error checker block checks for missing SOP and EOP

markers, for each port. If these markers are found to be missing, their respective

err_ry_msopN

and

err_ry_meopN

signals are asserted (high). These signals remain

high for one

rxsys_clk

cycle. These error conditions do not correlate directly—in

terms of latency—to the data going into, or coming out of, the FIFO buffer.

1 Altera recommends that you assert the

ctl_ax_fifo_eopdav

signal with the error

checker to ensure the buffer is emptied in the event of an overflow.

Atlantic buffer overflow

■ The Atlantic FIFO buffer error

checker block also handles

overflows

(

err_ry_fifo_oflwN

asserted).

■ If a packet is open when an

overflow occurs, the open

packet is closed and all

subsequent data associated

with that address is ignored

until an EOP associated with

that address is received.

■ Assert the

err_ry_fifo_oflwN

flag until the

FIFO buffer is flushed.

■ Any open packets are truncated with EOP and

ERR signal. If the last successful write

immediately before the overflow was an EOP, then

truncation is not necessary.

■ All further writes to the FIFO buffer are discarded

and ignored.

■ The FIFO buffer is drained (due to the assurance

that an EOP is in the FIFO buffer). Draining is

accomplished by the Atlantic sink logic (user

logic) as it continues to read data from the FIFO

buffer. Complete packets already written to the

FIFO buffer before the overflow occurred are not

corrupted and can be safely read.

■ Once the FIFO buffer is empty, the

err_ry_fifo_oflwN

is deasserted (low). Writes

to the FIFO buffer are ignored until a SOP is

received on that port.

Atlantic buffer underflow —

■ Assert

stat_aN_fifo_emptyN

for each Atlantic

FIFO buffer.

■ No loss of data if Atlantic compliant.

Table 4–4. Atlantic Error Handling (Part 2 of 2)

Error Condition Response

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 141 142

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