TDA4VH-Q1: SERDES Polarity Configuration Support

Antonio Steiger

Part Number: TDA4VH-Q1
Other Parts Discussed in Thread: TDA4VH

Tool/software:

Hello TI Engineering Team,

we would like to know whether SERDES lane polarity on TDA4VH can be configured and if so, what the procedure for it looks like. We are struggling to find any references to it in the reference manual / data sheet.

Here is our planned SERDES configuration:

This is our first embedded Linux design, so we are wondering how SERDES polarity configuration is typically done. Can we use the device tree for this?

Thank you for your time,

Antonio Steiger
Duneo
UnternehmerTUM / Venture Labs Startup, Munich

over 1 year ago

0 Takuma Fujiwara over 1 year ago

TI__Guru 60963 points

Hi Antonio,

I would recommend reading the Linux SDK documentation for SERDES as a starting point as this explains the hardware, software, and limitations: https://software-dl.ti.com/jacinto7/esd/processor-sdk-linux-j784s4/10_00_00_08/exports/docs/linux/Foundational_Components/Kernel/Kernel_Drivers/SERDES/SERDES.html

In terms of how this is set up in Linux, the following locations in code will be a good place to look at to get an idea for how the SERDES configuration is done in Linux:

This gives you what each lane can be configured as in device tree (J784S4=TDA4VH): https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/include/dt-bindings/mux/ti-serdes.h?h=ti-linux-6.1.y
The default SERDES lane configuration when using the TI J784S4 EVM with default SDK can be found in the EVM dts file: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-j784s4-evm.dts?h=ti-linux-6.1.y

Regards,

Takuma

0 Antonio Steiger over 1 year ago in reply to Takuma Fujiwara

Prodigy 30 points

Hello Takuma,

thank you for the overview. We understand how to assign IP to the different lanes, but none of the linked pages mention how to actually invert the polarity of a lane. The header file (your second link) mentions "SWAP" on USB IP, maybe this means the lane polarity is inverted? Or is there a register we missed that sets lane polarity?

This is crucial to know for PCB routing reasons.

0 Takuma Fujiwara over 1 year ago in reply to Antonio Steiger

TI__Guru 60963 points

Hi Antonio,

By polarity, if you mean RX/TX or P/N, SERDES comes in pairs of differential signals for TX/RX. Below is a screenshot from the schematic file available under "Design files" section of the EVM board product page: https://www.ti.com/tool/J784S4XEVM

Regards,

Takuma

0 Antonio Steiger over 1 year ago in reply to Takuma Fujiwara

Prodigy 30 points

Yes exactly, we mean mainly Positive / Negative. If the polarity of a particular SERDES differential pair (RX or TX) does not match the connected chip, we would have to reverse the polarity on the PCB. In the worst case this means having to run two vias per trace (four total), which we would like to avoid on high speed signals (e.g. 10Gb XFI). This is why it would be really convenient for us to swap the polarity in such cases. Many SoCs have this feature, I suspect TDA4VH has this too, we are just really struggling to find any references to it. Please see the following picture to better understand what I am referring to:

As you can see, the differential pairs need to connect, but the polarities do not match. I hope this gets the issue across better.

It didn't occur to us that RX/TX can also be swapped, that would of course also be very helpful.

Thank you for your time,

Antonio Steiger
Duneo
UnternehmerTUM / VentureLabs Startup

+1 Takuma Fujiwara over 1 year ago in reply to Antonio Steiger

TI__Guru 60963 points

Hi Antonio,

No swapping supported for RX/TX or P/N.

Regards,

Takuma

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TDA4VH-Q1: SERDES Polarity Configuration Support