Data Sheet

Ethernet Controller I210 —Interconnects
108
3.7.6.5.1 Setting the I210 Internal PHY to External Loopback Mode
For 1000 Mb/s, the following procedure should be used to put the I210 internal PHY into external
loopback mode:
• Set Link mode to PHY: CTRL_EXT.LINK_MODE = 00b
• In the PHY control register (Address 0 in the PHY):
— Set duplex mode (bit 8)
— Clear loopback bit (bit 14)
— Set auto-negotiation enable bit (bit 12)
• In the Checker Control (Page 6, PHY Register 18)
— Set Enable Stub Test (bit 3)
• Restart auto-negotiation (set bit 9)
• Reset the PHY (set bit 15).
• Wait for auto-negotiation to complete, then transmit and receive normally.
3.7.6.6 Line Loopback
In line loopback (Figure 3-13), MAC and SerDes interfaces are not functional and the data is sent from
a link partner to the PHY to test transmit and receive data paths. Frames that originate from a link
partner are looped back from the PHY and sent out on the wire before reaching the MAC interface pins.
The following should be confirmed before enabling the line loopback feature:
• The PHY must first establish a full-duplex link with another PHY link partner, either through auto-
negotiation or through forcing the same link speed.
In order to enable line loopback mode once the link is established, set bit 14 to 1b in the MAC Specific
Control Register 2 - Page 2, Register 21 (see Section 8.27.3.27).
Figure 3-13. Line Loopback
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