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Xilinx UG194 Virtex-5 FPGA Embedded Tri-Mode Ethernet MAC ...

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Chapter 3: Client Interface<br />

Normal Frame Reception<br />

CLIENTE<strong>MAC</strong>#RXCLIENTCLKIN<br />

The timing of a normal inbound frame transfer is shown in Figure 3-15. The client must<br />

accept data at any time; there is no buffering within the <strong>Ethernet</strong> <strong>MAC</strong> to allow for receive<br />

client latency. After frame reception begins, data is transferred on consecutive clock cycles<br />

to the receive client until the frame is complete. The <strong>Ethernet</strong> <strong>MAC</strong> asserts the<br />

E<strong>MAC</strong>#CLIENTRXGOODFRAME signal to indicate successful receipt of the frame and the ability<br />

to analyze the frame by the client.<br />

E<strong>MAC</strong>#CLIENTRXD[7:0]<br />

E<strong>MAC</strong>#CLIENTRXDVLD<br />

E<strong>MAC</strong>#CLIENTRXGOODFRAME<br />

E<strong>MAC</strong>#CLIENTRXBADFRAME<br />

Figure 3-15: Normal Frame Reception<br />

Frame parameters (destination address, source address, LT, data, and optionally FCS) are<br />

supplied on the data bus as shown in the timing diagram. The abbreviations are the same<br />

as those described in Table 3-1, page 52.<br />

If the LT field has a length interpretation, the inbound frame could be padded to meet the<br />

<strong>Ethernet</strong> minimum frame size specification. This padding is not passed to the client in the<br />

data payload; an exception is when FCS passing is enabled. See “Client-Supplied FCS<br />

Passing,” page 66.<br />

Therefore, when client-supplied FCS passing is disabled, E<strong>MAC</strong>#CLIENTRXDVLD is Low<br />

between frames for the duration of the padding field (if present), the FCS field, carrier<br />

extension (if present), the IFG following the frame, and the preamble field of the next<br />

frame. When client-supplied FCS passing is enabled, E<strong>MAC</strong>#CLIENTRXDVLD is Low between<br />

frames for the duration of carrier extension (if present), the IFG, and the preamble field of<br />

the following frame.<br />

Signal Timing of Good/Bad Frame Pulses<br />

DA SA L/T DATA<br />

<strong>UG194</strong>_3_15_072106<br />

Although the timing diagram in Figure 3-15 shows the E<strong>MAC</strong>#CLIENTRXGOODFRAME signal<br />

asserted shortly after the last valid data on E<strong>MAC</strong>#CLIENTRXD[7:0], this is not always the<br />

case. The E<strong>MAC</strong>#CLIENTRXGOODFRAME or E<strong>MAC</strong>#CLIENTRXBADFRAME signals are asserted only<br />

after completing all the frame checks. These frame checks occur only after receipt of any<br />

padding (if present), followed by the FCS and any carrier extension (if present). Therefore,<br />

either E<strong>MAC</strong>#CLIENTRXGOODFRAME or E<strong>MAC</strong>#CLIENTRXBADFRAME is asserted following frame<br />

reception at the beginning of the IFG.<br />

64 www.xilinx.com TE<strong>MAC</strong> User Guide<br />

<strong>UG194</strong> (v1.10) February 14, 2011<br />

R

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