Electronic – Broadcom Ethernet PHY link-up issue

ethernetsgmii

We are using BCM5482SA2KFBG PHY for ethernet link in SGMII mode by selecting INTSEL = 2'b10. The PHY was supposed to establish a link upon power up using Autonegotitation without any management configuration. PHY auto-negotiates to 10Mbps half duplex, though the PC and the PHY are capable of 1Gbps. The same 2 PHYs establish 1Gbps link with each other. Is there any other setting that is supposed to be done??
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This is how we have connected the interfaces as shown in the schematic.

Test cases:
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In this test, 2 different Broadcom PHYs in different boards(identical boards but not in the same board). The PHYs link up at 1Gbps (Autonegotiation – Autonegotiation done bit is high). We even created data traffic from one board and the data was received correctly in the other board.

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Test 2: This is what we aren't able to understand. The PHY does not connect to PC most of the times. We have to disable the SGMII interface for the PHY to link-up with PC (at 10Mbps with Autonegotiation). How does the SGMII interface affect the working of PHY ??

Test 3: We have another board with Marvell PHY which links correctly (1Gbps – Autonegotiation). Same PC, same ethernet.

Best Answer

The problem was with input frequency to the PHY. We were giving wrong frequency to the PHYs, but since the frequency was same on both the boards, they had no problem connecting at full speed with each other.