DS537 Datasheet, PDF (90/148 Pages) Xilinx, Inc – LogiCORE IP XPS LL TEMAC

LogiCORE IP XPS LL TEMAC (v2.03a)
VLAN Stripping
VLAN stripping allows the TEMAC to remove a VLAN tag in select Ethernet frames as they pass through the
xps_ll_temac core in either the transmit or receive direction.
X-Ref Target - Figure 58
Dest Srce VLAN Type
Addr Addr _{Tag /Len}
Data
FCS
4
bytes
Dest Srce Type
Addr Addr _/Len
Data
FCS
6
6
2 ^{46 - 1500 bytes normal} 4
bytes bytes bytes 46 - 9198 bytes jumbo bytes
Dest Srce VLAN VLAN Type
Addr Addr _{Tag Tag /Len}
4
bytes
Data
FCS
Dest Srce VLAN Type
Addr Addr _{Tag /Len}
Data
FCS
Figure 58: VLAN Stripping
DS537_58_091909
General
One VLAN tag will be removed:
• Non-VLAN frames will not be changed
• VLAN tagged frames will have the outer VLAN tag removed and we won’t check to see how many VLAN
tags it already has (if there are 4 tags we will make it 3).
When VLAN stripping 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 three VLAN stripping modes.
1. Do not strip tags from any frames
2. Strip one tag from all VLAN tagged frames
3. Strip one tag only from select VLAN tagged frames based on VID value
The third mode requires a method for specifying which tagged frames should be stripped. 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 strip enable field
for a TPID value indicates that frame should have its VLAN tag stripped.
Again, transmit In-Band FCS mode is not allowed and receive FCS stripping is required when using VLAN
stripping because FCS field value would not be correct for the frame with the VLAN tag removed. Please note that
although receive stripping is enabled, any padding if present will not be stripped due to the TYPE / LENGTH field
of the receive frame containing a VLAN tag rather than a length value.
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