Xilinx Virtex-4 User Manual
Also see for Virtex-4 RocketIO: User guideConfiguration user guide
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56 www.xilinx.com Embedded Tri-Mode Ethernet MAC User GuideUG074 (v2.2) February 22, 2010Chapter 3: Client, Host, and MDIO Interfaces RLength/Type Field Error ChecksLength/Type Field Error checking is specified in IEEE Std 802.3. The Length/Type FieldError checks consist of comparing the value in the Length/Type field with the actual size ofthe data field received. This check is only performed when the value in the Length/Typefield is less than 1536 (0x600). This check does not perform any checks on the total lengthof the frame. This functionality must be enabled to comply with this specification.Disabling Length/Type checking is intended only for specific applications, such as whenusing over a proprietary backplane.EnabledWhen Length/Type error checking is enabled (see “Receiver Configuration Register (Word1),” page 75), the following checks are made on frames with a value less than 1536 (0x600)in the Length/Type field. (If either of these checks fails, EMAC#CLIENTRXBADFRAME isasserted):• A value greater than or equal to decimal 46 but less than decimal 1536 (a lengthinterpretation) in the Length/Type field is checked against the actual data lengthreceived.• A value less than decimal 46 in the Length/Type field is checked to ensure the datafield is padded to exactly 46 bytes.Furthermore, if padding is indicated (the Length/Type field is less than decimal 46) andclient-supplied FCS passing is disabled, then the length value in the Length/Type field isused to deassert EMAC#CLIENTRXDVLD after the indicated number of data bytes,removing the padding bytes from the frame.DisabledWhen the Length/Type error checking is disabled (see “Receiver Configuration Register(Word 1),” page 75), the Length/Type error checks described above are not performed. Aframe containing only these errors causes EMAC#CLIENTRXGOODFRAME to beasserted. Disabling this check does not disable total frame length checks. Any frame of lessthan 64 total bytes (minimum frame size) or any frame exceeding the maximum frame sizechecks (if enabled) will still cause EMAC#CLIENTRXBADFRAME to be asserted. Controlframes will still be marked bad if they are not exactly 64 bytes in total length.Furthermore, if padding is indicated and client-supplied FCS passing is disabled, then alength value in the Length/Type field is not used to deassert EMAC#CLIENTRXDVLD.Instead EMAC#CLIENTRXDVLD is deasserted before the start of the FCS field; in thisway, any padding is not removed from the frame.Receive (RX) Client – 16-bit Wide InterfaceThis optional configuration can only be used when the Ethernet MAC is configured in1000BASE-X PCS/PMA mode. The frequency of the receive client clock is half thefrequency of the internal receive clock. The 16-bit client interface allows the Ethernet MACto run at an internal clock frequency of greater than 125 MHz. The interface allows theEthernet MAC to run at a line rate greater than 1 Gb/s as specified in IEEE Std 802.3.Therefore, the interface should not be used for Ethernet compliant applications, but it canbe useful for customer’s backplane applications.The PHYEMAC#RXCLK is used as the input clock port for theCLIENTEMAC#RXCLIENTCLKOUT divided by two, as shown in the receive client blockdiagram in Figure 3-2, page 39. Using a DCM with the receive client clock,www.BDTIC.com/XILINX |
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