Altera Triple Speed Ethernet MegaCore Function - Manual (Page 49)

Receive Thresholds
Figure 4-5: Receive FIFO Thresholds
Network
Switch Fabric
Frame Buffer n
Frame Buffer n - 1
Frame Buffer k
Frame Buffer 2
Frame Buffer 1
The remaining
unwritten entries in
the FIFO buffer
before it is full.
Almost full
The remaining
unread entries in
the FIFO buffer
before it is empty.
Almost empty
An early indication
that the FIFO
buffer is getting
full.
Section Empty
Sufficient unread
entries in the FIFO
buffer for the user
application to start
reading from it.
Section full
Table 4-6: Receive Thresholds
Description Register Name Threshold
The number of unread entries in the FIFO buffer before the buffer
is empty. When the level of the FIFO buffer reaches this threshold,
the MAC function asserts the
ff_rx_a_empty
signal. The MAC
function stops reading from the FIFO buffer and subsequently stops
transferring data to the user application to avoid buffer underflow.
When the MAC function detects an EOP, it transfers all data to the
user application even if the number of unread entries is below this
threshold.
rx_almost_empty
Almost
empty
Altera Corporation Functional Description
Send Feedback
4-13 Receive Thresholds
UG-01008
2014.06.30