GMII Transmission - 2.7 English

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

Document ID
PG292
Release Date
2022-05-11
Version
2.7 English

1/2.5 Gb/s Frame Transmission

The timing of normal outbound frame transfer is shown in the following figure.

Figure 1. GMII Frame Transmission at 1 Gb/s

100 Mb/s Frame Transmission

At 100 Mb/s the operation of the core remains unchanged. It is the responsibility of the client logic (for example, an Ethernet MAC) to enter data at the correct rate. When operating at 100 Mb/s, every byte of the MAC frame (from preamble to the Frame Check Sequence field, inclusive) should be repeated for 10 clock periods to achieve the desired bit rate, as shown in the following figure. The core always expects eight bits from the client logic.

Figure 2. GMII Data Transmission at 100 Mb/s

10 Mb/s Frame Transmission

At 10 Mb/s the operation of the core remains unchanged. It is the responsibility of the client logic (for example, an Ethernet MAC), to enter data at the correct rate. When operating at 10 Mb/s, every byte of the MAC frame (from preamble to the frame check sequence field, inclusive) should be repeated for 100 clock periods to achieve the desired bit rate. It is also the responsibility of the client logic to ensure that the interframe gap period is legal for the current speed of operation. The core always expects eight bits from the client logic.