46.4.11.1 Receive FIFO
Four programmable thresholds are available, which can be set to any value to control the
core operation as follows.
Table 46-79. Receive FIFO Thresholds Definition
Register
Description
ENET
n
_RSFL
[RX_SECTION_
FULL]
When the FIFO level reaches the ENET
n
_RSFL value, the MAC status signal is asserted to indicate that
data is available in the receive FIFO (cut-through operation). Once asserted, if the FIFO empties below
the threshold set with ENET
n
_RAEM and if the end-of-frame is not yet stored in the FIFO, the status
signal is deasserted again.
If a frame has a size smaller than the threshold (i.e. an end-of-frame is available for the frame), the status
is also asserted.
To enable store and forward on the receive path, clear ENET
n
_RSFL. the MAC status signal is asserted
only when a complete frame is stored in the receive FIFO.
When programming a non-zero value to ENET
n
_RSFL (cut-through operation) it should be greater than
ENET
n
_RAEM.
ENET
n
_RAEM
[RX_ALMOST_E
MPTY]
When the FIFO level reaches the ENET
n
_RAEM value, and the end-of-frame has not been received, the
core receive read control stops the FIFO read (and subsequently stops transferring data to the MAC client
application).
It continues to deliver the frame, if again more data than the threshold or the end-of-frame is available in
the FIFO.
Set ENET
n
_RAEM to a minimum of six.
ENET
n
_RAFL
[RX_ALMOST_F
ULL]
When the FIFO level comes close to the maximum, so that there is no more space for at least
ENET
n
_RAFL number of words, the MAC control logic stops writing data in the FIFO and truncates the
received frame to avoid FIFO overflow.
The corresponding error status is set when the frame is delivered to the application.
Set ENET
n
_RAFL to a minimum of 4.
ENET
n
_RSEM
[RX_SECTION_
EMPTY]
When the FIFO level reaches the ENET
n
_RSEM value, an indication is sent to the MAC transmit logic,
which generates a XOFF pause frame. This indicates FIFO congestion to the remote Ethernet client.
When the FIFO level goes below the value programmed in ENET
n
_MRBR, an indication is sent to the
MAC transmit logic, which generates a XON pause frame. This indicates the FIFO congestion is cleared
to the remote Ethernet client.
Clearing ENET
n
_RSEM disables any pause frame generation.
Functional Description
K53 Sub-Family Reference Manual, Rev. 6, Nov 2011
1240
Freescale Semiconductor, Inc.
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