DS537 Datasheet, PDF (89/148 Pages) Xilinx, Inc – LogiCORE IP XPS LL TEMAC

LogiCORE IP XPS LL TEMAC (v2.03a)
General
One VLAN tag will be added depending on mode of operation:
• Non-VLAN frames will get one VLAN tag added to become single VLAN tagged frames.
• VLAN tagged frames will receive another VLAN tag and no checking will be performed to see how many
VLAN tags the frame already has (if there are already 3 tags it will now have 4).
Therefore, in cases that require adding a VLAN tag, one VLAN tag will be added to the existing frame.
The TEMAC core’s basic VLAN mode extends the maximum normal frame size validation by 4 bytes. This mode
does not extend to multiple VLAN tagging. Multiple VLAN frames that exceed 1522 bytes would be discarded as
too long. As mentioned previously, this requires the use of jumbo frame mode which will eliminate the automatic
invalidation of frames that normally would be too large for "normal" frame sizes.
When VLAN tagging is enabled at build time with the appropriate parameter, a field in the Reset and Address Filter
Registers (RAF0 and RAF1) will be used to select one of four VLAN tagging modes and the Transmit VLAN Tag
Register (TTAG0 and TTAG1) and Receive VLAN Tag Register (RTAG0 and RTAG1) will be used to hold the VLAN
tag value which will be inserted.
The four VLAN tagging modes which are selectable at run time are:
1. Do not add tags to any frames
2. Add one tag to all frames
3. Add one tag only to frames that are already VLAN tagged
4. Add one tag only to select frames that are already VLAN tagged based on VID value
The forth mode requires a method for specifying which tagged frames should receive an additional VLAN tag. The
Transmit VLAN Data Table (0 and 1) and Receive VLAN Data Table (0 and 1) are used for this purpose. A 1 in the
tag enable field for a TPID value indicates that frame should receive an additional tag.
Again, transmit In-Band FCS mode is not allowed and receive FCS stripping is required when using VLAN tagging
because FCS field value would not be correct for the frame with the additional VLAN tag. Although receive
stripping is enabled, any padding if present will not be stripped because the TYPE / LENGTH field of the receive
frame contains a VLAN tag rather than a length value. However, the length field is still present.
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