help! Ethernet PHY Loopback problem

Hi guys, A problem concering broadcom PHY 5461 loopback mode(internal loopback).from mac ----phy----mac the phy works well on 100M loopback, but cannot works in 1000M mode,i am sure regiser setting are write correctly.

A strange problem is : when i ping from another swith(not in loopback mode), 5461phy can received data correctly , and mac connected with 5461 return arp requset to phy, but, 5461 cannot transmitted the data,using oscilliscope, i can see the data on 5461 TX pins, it means mac succefully transmit data to 5461,

now we consider loopback again,since we can receive data, and mac can transmit data, why the phy cannot loop the data back to MAC

any advice from you would be great help!

Reply to
jasonleehan
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Jason,

I've never worked with the 5461 but most PHYs have different register write sequences for different loopback modes. Draw a picture of what you want to do and check your register write sequence again. The fact that 100BASE-TX works but 1000BASE-T does not seems to indicate that

1000BASE-T is not auto-negotiating properly (1000BASE-T is master/ slave timing system.) You cannot force 1000BASE-T to link, you must auto-negotiate.

regards, Kadir "Solid Gold" Suleyman

Reply to
Kadir Solid Gold Suleyman

The clocking schemes for 10/100 (MII) are different from 1000 (GMII). The clocks also go in different directions. At 10/100, the MAC is driven by the PHY's TXCLK. At 1000, the PHY is driven by the MAC's GTXCLK.

One simple test would be that if you can achieve a gigabit link and

*receive* packets but not *send* them.
--
Ben Jackson AD7GD

http://www.ben.com/
Reply to
Ben Jackson

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