fido2100 3-Port Industrial Ethernet DLR Switch with IEEE1588
Data Sheet
April 10, 2013
The MAC will drop frames received with errors signaled by the PHY device and those with frame
check sequence (CRC) errors. It will drop frames shorter than 64 bytes as per IEEE 802.3 specification.
It will drop frames longer than maximum IEEE 802.3 tagged frame size of 1522 bytes. The MAC will
also drop frames with alignment error, i.e. those having a non-integral number of bytes.
2.1.1 IEEE 802.3 Full Duplex Flow Control
The fido2100 implements IEEE 802.3 compliant full duplex flow control using PAUSE frames. In
order to provide optimum performance, a special set of rules are followed for PAUSE frame generation
and reception.
PAUSE frame reception is enabled on external ports operating in full duplex mode and transmission on
the port through which the PAUSE frame was received will be suspended for specified pause duration
in the PAUSE frame. PAUSE frame reception is always disabled on the internal port, since the host
CPU will always have enough memory for its communications.
If speed and duplex modes of external ports are same and when buffer usage on either one of external
ports reaches 95% of buffer capacity, a PAUSE frame will be generated from internal port to host CPU
with maximum pause duration. If the buffer situation has not improved at the end of pause duration,
additional PAUSE frames will be generated from internal port as needed. When buffer usage on both
external ports reaches below 85% of buffer capacity, a PAUSE frame will be generated on internal port
with zero pause duration to cancel pause. If speed and duplex modes of external ports are not same,
PAUSE frames will not be generated.
For external ports, PAUSE frame generation on a port is enabled only for full duplex mode and when
both external ports have same speed and duplex settings. When a first external port is operating in full
duplex mode and buffer usage on internal port or second external port reaches 95% of buffer capacity a
PAUSE frame will be generated on first external port with maximum pause duration. If the buffer
situation has not improved at the end of pause duration, additional PAUSE frames will be generated
from first external port as needed. When buffer usage on both internal and second external ports
reaches below 85% of buffer capacity, a PAUSE frame will be generated on first external port with
zero pause duration to cancel pause. If speed and duplex modes of external ports are not same, PAUSE
frames will not be generated.
Obviously, for flow control on fido2100 to work properly, the integrated MAC on host CPU must
support flow control as well. Most Ethernet microprocessors do support this capability and dual port
product designer must ensure that the selected host CPU supports flow control.
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