AM69A: PCIe data line order swap

Xingyu Zhu

Part Number: AM69A

Tool/software:

Hi expert,

Our customer connect PCIe_N and PCIe_P in wrong order by mistake. They would like to know if they can adjust the order by software? Thanks

Best Regards,

Xingyu Zhu

4 months ago

0 Takuma Fujiwara 4 months ago

TI__Guru 50723 points

Hi Xingyu,

From software-side, I am not aware of anything adjustable for PCIe P/N polarity.

As far as I know, I have heard in past that complete lane reversal (which is different from polarity reversal) is possible and this is handled by hardware. I see that polarity is also possible hardware-wise from this past E2E ticket that the hardware team has responded to: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1219261/tda4vh-q1-can-the-pcie-interface-swap-lanes-and-p-n-for-better-layout?tisearch=e2e-sitesearch&keymatch=pcie%25252525252520p%25252525252520n%25252525252520swap#. However, I am not sure if that is also all handled by hardware, and if not, whether it is possible to handle in software.

Let me check with the internal software development team to see if they have seen the polarity swap before.

Regards,

Takuma

0 Xingyu Zhu 4 months ago in reply to Takuma Fujiwara

TI__Expert 4295 points

Hi Takuma,

Thanks for your reply. Please help to confirm internally.

+1 Takuma Fujiwara 4 months ago in reply to Xingyu Zhu

TI__Guru 50723 points

Hi Xingyu,

I have gotten confirmation from our hardware team that polarity inversion is supported automatically by hardware per PCIe spec. No SW required to adjust this.

To quote:

"""

From PCIe Spec:
"4.2.4.4
During the training sequence in Polling, the Receiver looks at Symbols 6-15 of the TS1 and TS2 20 Ordered Sets as the indicator of Lane polarity inversion (D+ and D- are swapped). If Lane polarity inversion occurs, the TS1 Symbols 6-15 received will be D21.5 as opposed to the expected D10.2. Similarly, if Lane polarity inversion occurs, Symbols 6-15 of the TS2 Ordered Set will be D26.5 as opposed to the expected D5.2. This provides the clear indication of Lane polarity inversion.
If polarity inversion is detected the Receiver must invert the received data. The Transmitter must 25 never invert the transmitted data. Support for Lane Polarity Inversion is required on all PCI Express Receivers across all Lanes independently. "

"""

Regards,

Takuma

0 Xingyu Zhu 4 months ago in reply to Takuma Fujiwara

TI__Expert 4295 points

Thanks for your detailed reply. It is helpful. Our customer also would like to know if they can swap RX and TX?

0 Takuma Fujiwara 4 months ago in reply to Xingyu Zhu

TI__Guru 50723 points

Hi Xingyu,

That is answered in this E2E thread I posted before if you mean lane reversal: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1219261/tda4vh-q1-can-the-pcie-interface-swap-lanes-and-p-n-for-better-layout?tisearch=e2e-sitesearch&keymatch=pcie%25252525252520p%25252525252520n%25252525252520swap

To quote:

"""

Tx / Rx must go together. So either standard config or complete reversal for both Tx and Rx.

"""

Or, do you mean the customer is trying to receive on the TX and transmit on the RX?

Regards,

Takuma

0 Xingyu Zhu 4 months ago in reply to Takuma Fujiwara

TI__Expert 4295 points

Hi Takuma,

Takuma Fujiwara said:
Or, do you mean the customer is trying to receive on the TX and transmit on the RX?

Yes, customer would like know if we support this?

+1 Takuma Fujiwara 4 months ago in reply to Xingyu Zhu

TI__Guru 50723 points

Hi Xingyu,

No.

Regards,

Takuma

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AM69A: PCIe data line order swap