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Receiving Inbound Frames
Maximum Permitted Frame Length
The maximum legal length of a frame specified in IEEE 802.3-2005 is 1518 bytes for non-
VLAN tagged frames. VLAN tagged frames may be extended to 1522 bytes. When jumbo
frame handling is disabled and the core receives a frame which exceeds the maximum
legal length, rx_bad_frame is asserted. When jumbo frame handling is enabled, frames
which are longer than the legal maximum are received in the same way as shorter frames.
For more information about enabling and disabling jumbo frame handling, see
"Configuration Registers," on page
Length/Type Field Error Checks
Enabled
Default operation is with the length/type error checking enabled (see
Configuration," on page
received. If either of these checks fail, the frame is marked as bad.
•
•
Furthermore, if padding is indicated (the length/type field is less than decimal 46) and
client-supplied FCS passing is disabled, the length value in the length/type field will be
used to deassert rx_data_valid after the indicated number of data bytes so that the
padding bytes are removed from the frame. See
Disabled
When the length/type error checking is disabled and the length/type field has a length
interpretation, the MAC does not check the length value against the actual data length
received. See
marked as good.
However, if the length/type field is less than decimal 46 then the MAC will mark a frame
as bad if it is not the minimum frame size of 64 bytes.
If padding is indicated and client-supplied FCS passing is disabled, then a length value in
the length/type field will not be used to deassert rx_data_valid. Instead,
rx_data_valid is deasserted before the start of the FCS field, and any padding is not
removed from the frame.
1-Gigabit Ethernet MAC v8.5 User Guide
UG144 April 24, 2009
-- DISCONTINUED PRODUCT --
79). In this mode, the following checks are made on all frames
A value in the length/type field that is greater than or equal to decimal 46, but less
than decimal 1536 (a length interpretation), is checked against the actual data length
received.
A value in the length/type field that is less than decimal 46 is checked to see that the
data field is padded to exactly 46 bytes (so that the resultant frame is a minimum
frame size of 64 bytes total in length).
"Receiver Configuration" in Chapter
www.xilinx.com
78.
"Client-Supplied FCS Passing."
8. A frame containing only this error is
R
"Receiver
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