Table 46-80. Transmit FIFO Thresholds Definition (continued)
Register
Description
ENET
n
_TFWR
When the FIFO level reaches the ENET
n
_TFWR value and when STRFWD is cleared, the MAC transmit
control logic starts frame transmission before the end-of-frame is available in the FIFO (cut-through
operation).
If a complete frame has a size smaller than the ENET
n
_TFWR threshold, the MAC also transmits the
frame to the line.
To enable store and forward on the transmit path, set STRFWD. In this case, the MAC starts to transmit
data only when a complete frame is stored in the transmit FIFO.
MAC transmit
FIFO write control
(FIFO write control)
TAFL - Almost full
TAEM - Almost empty
TSEM - Section empty
TFWR - Section full
(MAC read control)
(Core FIFO status)
(MAC transmit start)
Figure 46-62. Transmit FIFO Overview
46.4.12 Loopback Options
The core implements external and internal loopback options, which are controlled by the
following ENETn_RCR register bits:
Table 46-81. Loopback Options
Register Bit
Description
LOOP
Internal MII loopback. The MAC transmit is returned to the MAC receive. No data is transmitted to the
external interfaces.
In MII internal loopback, MII_TXCLK and MII_RXCLK must be provided with a clock signal (2.5MHz for
10Mbps and 25MHz for 100Mbps)
Functional Description
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