DP83869HM: Recovered clock - SGMII

Alexey Tsirlin

Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Hi,

I am planning to use DP83869 PHY in SyncE application. IO_MUX_CFG register allows configuring the recovered clock to be linked to one of the 4 reception channels, I guess the reception channels are 4 Copper pairs. I am also required to support SFP cage. From my understanding, for the SFP cage I will need RGMII-SGMII mode or RGMII-1000-X modes of operation. How recovered clock works in those modes?

From the following thread https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1480227/dp83869hm-can-we-get-clock-output-that-recovered-from-sgmii-when-dp83869-is-in-rgmii-to-sgmii-bridge-mode I have learned that it is impossible. But it is still not clear to me how it works as the RGMII RX CLK should also outputs recovered clock. What clock does it output in case of RGMII-SGMII mode or in RGMII-1000-X modes?

I have performed the following test - I have configured the CLK_OUTPUT to recovered clock on channel A and compared it with the RX CLK signals and those signals have the same frequency which is not exactly the same frequency as local clock.

Thanks!

Alexey.

7 months ago

0 J 7 months ago

TI__Mastermind 26771 points

Hi Alexey,
RGMII normally uses recovered clock from the MDI signal for its RX_CLK on DP83869.
In fiber connection, the clock is recovered in the same manner as the copper connection does.
In the bridge mode, there is no recovered clock from the MDI. However, we set which side of the signaling connects to the MAC so that the PHY knows which side to recover its clock for the MAC signaling.

Best,
J

0 Alexey Tsirlin 7 months ago in reply to J

Prodigy 85 points

Hi J,

So, is there are way for me to get the recovered RX clock for SyncE operation while I am in RGMII-SGMII mode and in RGMII-1000BaseX mode?

I came across the following thread: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/986350/dp83869hm-is-rx_clk-sychronized-to-the-transmit-clock-of-the-partner-in-rgmii-to-1000base-x-mode where it is suggested by TI team to configure the IO_MUX_CFG [12:8] bits to 12h which is undocumented option. They claim that this option outputs recovered clock from SGMII on the CLK_OUT pin. Is it correct?

Thanks!

Alexey.

+1 J 7 months ago in reply to Alexey Tsirlin

TI__Mastermind 26771 points

Hi Alexey,

I verified that the described configuration in the E2E post gives out 125MHz recovered clock for fiber so that can be used.

Best,

Interface

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DP83869HM: Recovered clock - SGMII