DS537 Datasheet, PDF (77/148 Pages) Xilinx, Inc – LogiCORE IP XPS LL TEMAC

LogiCORE IP XPS LL TEMAC (v2.03a)
FCS Pass Through
The XPS_LL_TEMAC can calculate and add the FCS field to each transmitted frame or it can pass through an FCS
field supplied with the frame data by the user. When a user supplied FCS field is passed through, the user must
supply padding as necessary to ensure that the frame meets the minimum frame length requirement. FCS insertion
or pass through is controlled by the TC register bit 29 (page 53).
Virtual LAN (VLAN) Frames
When transmitting VLAN frames (if enabled by the TC register bit 27 page 53) without extended VLAN mode, the
user must supply the VLAN type tag 0x8100 a well as the two byte tag control field along with the rest of the frame
data. More information about the tag control field is available in the IEEE Std 802.3-2002 specification.
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 (TC
register bit 30 page 53) and the user attempts to transmit a frame that exceeds the maximum legal length, the
XPS_LL_TEMAC inserts an error code to corrupt the current frame and the frame is truncated to the maximum
legal length. When jumbo frame handling is enabled, frames longer then the legal maximum are transmitted error
free. Jumbo frames are restricted by the XPS_LL_TEMAC design to less than 16K Bytes.
Frame Reception
Frame Reception with Errors
An unsuccessful frame reception (for example, a fragment frame or a frame with an incorrect FCS) will be dropped
and not passed to the user. A Receive Reject interrupt will be activated (see bit 28 in Table 12).
FCS Pass Through or Stripping
If the Length/Type field has a length interpretation, the received frame could be padded to meet the minimum
frame size specification. If FCS Pass Through is disabled (RCW1 register bit 29 page 51) and Length/Type filed
error checking is enabled (RCW1 register bit 25 page 51), the padding is stripped along with the FCS field and is not
passed to the user. If FCS Pass Through is disabled (RCW1 register bit 29 page 51) and Length/Type field error
checking is also disabled, the padding is not stripped and is passed to the user but the FCS field is stripped and is
not passed to the user.
If the FCS Pass Through is enabled, any padding will be passed to the user along with the FCS field. Even though
the FCS is passed up to the user, it is also verified and the frame will be dropped if the FCS is incorrect. A Receive
Reject interrupt will be activated (see bit 28 in Table 12).
Table 57: Receive Frame FCS Field and Pad Field Stripping or Pass Through
FCS Pass Through
(RCW1 register bit 29 = 1)
FCS Strip
(RCW1 register bit 29 = 0)
Length/Type field error check
(RCW1 register bit 25 = 0)
FCS and padding (if present) fields
passed to user for all accepted frames
FCS and padding (if present) fields
stripped and not passed to user for all
accepted frames
Length/Type field error ignore
(RCW1 register bit 25 = 1)
FCS and padding (if present) fields
passed to user for all accepted frames
FCS field stripped and not passed to
user but padding (if present) passed to
user for all accepted frames
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