GMI Transmission - 2.7 English

1G/10G/25G Switching Ethernet Subsystem Product Guide (PG292)

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2.7 English

This section includes figures that illustrate GMII transmission. In these figures the clock is not labeled. The source of this clock signal varies, depending on the options selected when the core is generated.

Normal Frame Transmission

Normal outbound frame transfer timing is shown in the following figure. This figure shows that an Ethernet frame is proceeded by an 8-byte preamble field (inclusive of the Start of Frame Delimiter (SFD)), and completed with a 4-byte Frame Check Sequence (FCS) field. This frame is created by the MAC connected to the other end of the GMII. The PCS logic itself does not recognize the different fields within a frame and treats any value placed on gmii_txd[7:0] within the gmii_tx_en assertion window as data.

Figure 1. GMII Normal Frame Transmission

Error Propagation

A corrupted frame transfer is shown in the following figure. An error can be injected into the frame by asserting gmii_tx_er at any point during the gmii_tx_en assertion window. The core ensures that all errors are propagated through both transmit and receive paths so that the error is eventually detected by the link partner.

Figure 2. GMII Error Propagation Within a Frame