DP83TG720S-Q1: RGMII cannot communicate

Hi Amy,

It's possible this is an RGMII timing problem between the MAC and PHY.

Please try testing the device in RGMII shift mode by strapping RX_D2 and RX_D1 high.

Shift mode can also be enabled by programming register 0x602[1:0] = '11', and the shift delay can be tuned using register 0x430[11:4].

This FAQ is a useful reference for selecting the correct RGMII delay mode.

Thank you,

Evan

Hi Evan,

Thank you for your assistance. The following is the customer feedback, could you please give your comments.

I tried this advice:Enable shift mode by programming register 0x602 [1:0] = '11'; and all TX delay values were tried on register 0x430[11:8].

(Why did I not change the RX delay because there are many ways to combine the two delays and I intend to switch on the tx link first.）

My test equipment is "VECTOR VN5620". I haven't seen the data coming from VN5620.I would like to ask if this method of only looking at TX data and only adjusting TX delay is correct?

The following figure shows the waveform on the TX link：

Below I dump the relevant registers for use with reference:

This data goes from MAC to PHY. Is there any way to check whether the phy is receiving data correctly?

My MAC terminal uses SJA1110, have you tried this combination?

Thanks,

Amy

Hi Amy,

If the TX/RX traces between the MAC and PHY are length-matched, I recommend testing with the same delay applied to both TX and RX in shift mode.

To check if the PHY is receiving the data from the MAC:

Enable RGMII loopback with reg<0x0000> = 0x4140, and probe the RGMII RX pins to see if the same data from the MAC is looped back. Register 0x063C[15:0] reports the total received packets, this can be compared to the number of packets sent from the MAC.

Thank you,

Evan