Ethernet LED blinking changes DAC voltage

[lneuhaus]

When the ethernet LED on a Stemlab125-14 blinks, this results in a change in DAC voltage of the order of ~0.5 mV. We have confirmed this correlation with a photodetector placed near the ethernet port LED. I believe the linux OS ethernet driver is responsible for this blinking. Is there a way to disable it to get the best possible noise performance out of a redpitaya?

[jeras]

Ethernet port blinking probably can be controlled through the devicetree.

This is the device tree file to modify:
https://github.com/RedPitaya/RedPitaya/blob/master/fpga/dts/ethernet.dtsi

This describes the available led options:
https://github.com/RedPitaya/linux-xlnx/blob/branch-redpitaya-v2017.2/include/dt-bindings/phy/phy-leds.h

This is the Lantiq PHY linux driver source:
https://github.com/RedPitaya/linux-xlnx/blob/branch-redpitaya-v2017.2/drivers/net/phy/lantiq.c

If the change could not be applied at runtime, then the simplest approach would be to create an alternative .dtb file, and overwrite the original on the SD card FAT partition.

It has been a couple of years since I last worked with devicetree, so you will probably have to find somebody else to help with how to properly apply it.

[lneuhaus]

Thanks for these hints. I was able to solve it using https://github.com/PieVo/mdio-tool in the following way:

ssh root@my-redpitaya-hostname
git clone https://github.com/PieVo/mdio-tool.git
cd mdio-tool
cmake .
make
./mdio-tool w eth0 0x1b 0x0000

To re-enable blinking, run

./mdio-tool w eth0 0x1b 0x0f00

The registers addresses and lots of more info can be found at https://datasheet.octopart.com/PEF-7071-V-V1.5-Lantiq-datasheet-62314344.pdf, e.g. page 126.

If anyone knows how I have to modify the .dtsi-file that would be great!

[lneuhaus]

Something like

 
/*
 * Lantiq ethernet PHY 
 */
&gem0 {
	phy-handle = <&ethernet_0_mdio>;
	ethernet_0_mdio: ethernet_0_mdio@1 {
		reg = <1>;
		reg = <0x1b 0x0000>;
	};
};

maybe?

[lneuhaus]

Is this fixed by fbbbde8? Is a usage example for the command-line tool to disable ethernet LEDs available?

[crtvalentincic]

This feature is available in the latest beta release 1.04-11, usage example can be seen here: https://redpitaya.readthedocs.io/en/latest/appsFeatures/command_line_tools/com_line_tool.html#led-enable-disable-utility