K60P100M100SF2RM Datasheet, PDF (1211/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 44 10/100-Mbps Ethernet MAC (ENET)
FIFO read control
RSFL - Section full
RAEM - Almost empty
(FIFO read control)
RSEM - Section empty RAFL - Almost full
(Pause frame (FIFO write protection)
generation)
MAC receive
Figure 44-61. Receive FIFO Overview
44.4.11.2 Transmit FIFO
Four programmable thresholds are available which control the core operation as
described below.
Table 44-80. Transmit FIFO Thresholds Definition
Register
ENETn_TAEM
[TX_ALMOST
_EMPTY]
ENETn_TAFL
[TX_ALMOST
_FULL]
ENETn_TSEM
[TX_SECTION
_EMPTY]
Description
When the FIFO level reaches the ENETn_TAEM value and no end-of-frame is available for the frame, the
MAC transmit logic avoids a FIFO underflow by stopping FIFO reads and transmitting the Ethernet frame
with an MII error indication.
Set ENETn_TAEM to a minimum of 4.
When the FIFO level approaches the maximum, so that there is no more space for at least ENETn_TAFL
number of words, the MAC deasserts its control signal to the application.
If the application does not react on this signal, the FIFO write control logic avoids FIFO overflow by
truncating the current frame and setting the error status. As a result, the frame is transmitted with an MII
error indication.
Set ENETn_TAFL to a minimum of 4. Larger values allow more latency for the application to react on the
MAC control signal deassertion, before the frame is truncated. A typical setting is 8, which offers 3–4
clock cycles of latency to the application to react on the MAC control signal deassertion.
When the FIFO level reaches the ENETn_TSEM value, a MAC status signal is deasserted to indicate that
the transmit FIFO is getting full.
This gives the application an indication to slow or stop its write transaction to avoid a buffer overflow.
This is a pure indication function to the application. It has no effect within the MAC.
When ENETn_TSEM is 0, the signal is never deasserted.
Table continues on the next page...
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1211