MAC Loopback

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

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2.4 English

MAC local loopback can be enabled on MII/GMII by setting the GEM{0:3}.network_control[loopback_local] = 1.

In MAC internal loopback mode, both transmit and receive clock are sourced from the internal Ethernet reference clocks (see GEM Ref clock internal clock source in Figure This Figure).


IMPORTANT:   Receive and transmit must be disabled when making the switch into and out of internal loopback because the clocks provided might glitch while switching to the loopback reference clock.

Also, TBI mode must be disabled for internal loopback by setting GEM{0:3}.network_config[pcs_select] = 0.