The RGMII specification specifies a rise time of 0.75ns max. Looking at the STM32MP151A datasheet I can't select a speed setting to match this specification, they are all to slow. In the AN5031 a "High speed" selection is recommended. Do I miss something?

[PatrickF]

Hi,

STM32MP15 datasheet specify tr/tf for 10%/90% 1.8V or 3.3V on specified capacitive load whereas RGMII v2.0 specify it for 20%/90% at 1.5V without any details on the load.

Most RGMII PHYs uses in fact 1.8V or 3.3V levels.

The 0.75ns is quite aggressive for 3.3V swing and probably also over-specified for a 8ns cycle period.

I confirm that STM32MP15 is working well with many different RGMII model and vendors.

As mentioned in AN5031, you should select high-speed for RGMII IOs (i.e. IOSPEEDR=2) and in case VDD=1.8V, HSLVEN_ETH = 1.

All this is natively managed by device tree and visible in examples provided.

e.g. https://github.com/STMicroelectronics/u-boot/blob/v2021.10-stm32mp/arch/arm/dts/stm32mp15-pinctrl.dtsi#L244

Regards.

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