This section includes figures that illustrate GMII reception. In these figures, the clock is not labeled. The source of this clock signal varies, depending on the options used when the core is generated.
Normal Frame Reception
The timing of normal inbound frame transfer is illustrated in the following figure. This shows that Ethernet frame reception is proceeded by a preamble field. The (see clause 35) allows for up to all of the seven preamble bytes that proceed the Start of Frame Delimiter (SFD) to be lost in the network. The SFD is always present in well-formed frames.
Normal Frame Reception with Extension Field
In accordance with the IEEE 802.3-2008 Specification [Ref 2], clause 36, state
machines for the 1000BASE-X PCS, gmii_rx_er_chx can
be driven High following reception of the end frame with gmii_rxd_chx[7:0] containing the hexadecimal value of 0x0F to signal
carrier extension. This is illustrated in the following figure. This is not an error
condition and can occur even for full-duplex frames.
This is not an error condition and can occur even for full-duplex frames.
Frame Reception with Errors
The signal gmii_rx_er_chx when
asserted within the assertion window signals that a frame was received with a
detected error (following figure). In addition, a late error can also be detected
during the Carrier Extension interval. This is indicated by gmii_rxd_chx[7:0] containing the hexadecimal value 0x1F, also
illustrated in the following figure.