DS537 Datasheet, PDF (78/148 Pages) Xilinx, Inc – LogiCORE IP XPS LL TEMAC

LogiCORE IP XPS LL TEMAC (v2.03a)
Virtual LAN (VLAN) Frames
Received VLAN tagged frames will be passed to the user if VLAN frame reception is enabled (RCW1 register bit 27
page 51). This is the basic native VLAN support provided by the TEMAC core. For more information about
extended VLAN functions, please refer to those sections which follow.
Maximum Frame Length and Jumbo Frames
The maximum length of a frame specified in the IEEE Std 802.3-2002 specification is 1518 bytes for non-VLAN
tagged frames. VLAN tagged frames can be extended to 1522 bytes. When jumbo frame handling is disabled
(RCW1 register bit 30 page 51) and a received frame exceeds the maximum legal length, the frame is dropped and
a Receive Reject interrupt will be activated (see bit 28 in Table 12). When jumbo frame handling is enabled, frames
longer then the legal maximum are received in the same way as shorter frames. Jumbo frames are restricted by the
XPS_LL_TEMAC design to less than 16K Bytes.
Length/Type Field Error Checks
Length/Type field error checking is specified in IEEE Std 802.3. This functionality must be enabled (RCW1 register
bit 25 page 51) to comply with this specification. Disabling Length/Type checking is intended only for specific
applications, such as when using over a proprietary backplane.
Enabled
When Length/Type error checking is enabled, the following checks are made on all frames received. (If either of
these checks fails, the frame is dropped and a Receive Reject interrupt will be activated (see bit 28 in Table 12).
• A value greater than or equal to decimal 46 but less than decimal 1536 in the length/type field is checked
against the actual data length received.
• A value less than decimal 46 in the length/type field is checked to ensure the data field is padded to exactly 46
bytes. The resultant frame is now the minimum frame size: 64 bytes total in length.
Additionally, if FCS passing is disabled, the length/type field will be used to strip the FCS field AND any padding
that may exist. NEITHER will be passed to the user.
Disabled
When the length/type error checking is disabled, the length/type error checking above is not performed and a
frame that has only these errors will be accepted.
Additionally, if FCS passing is disabled, the length/type field is NOT used to determine padding that may exist and
the FCS field WILL be stripped but any padding that may exist in the frame WILL NOT be stripped and WILL be
passed to the user.
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