K60P100M100SF2RM Datasheet, PDF (1210/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
44.4.11.1 Receive FIFO
Four programmable thresholds are available, which can be set to any value to control the
core operation as follows.
Table 44-79. Receive FIFO Thresholds Definition
Register
Description
ENETn_RSFL
[RX_SECTION_
FULL]
When the FIFO level reaches the ENETn_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 ENETn_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 ENETn_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 ENETn_RSFL (cut-through operation) it should be greater than
ENETn_RAEM.
ENETn_RAEM When the FIFO level reaches the ENETn_RAEM value, and the end-of-frame has not been received, the
[RX_ALMOST_E
MPTY]
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 ENETn_RAEM to a minimum of six.
ENETn_RAFL When the FIFO level comes close to the maximum, so that there is no more space for at least
[RX_ALMOST_F
ULL]
ENETn_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 ENETn_RAFL to a minimum of 4.
ENETn_RSEM
[RX_SECTION_
EMPTY]
When the FIFO level reaches the ENETn_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 ENETn_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 ENETn_RSEM disables any pause frame generation.
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K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.