Why did ST assign a pin to their official board and software when it can't even be configured in CubeMX?

[jmh8231]

Looking at the Ethernet PHY circuit of the STM32H735G-DK, the MCU and MAC are connected via the RMII interface, and a pin named "RMII_RX_ER" is connected to the MCU.

However, if you configure it for RMII in CubeMX (version 6.18.1), this pin does not activate normally. If the user manually activates it with the mouse, the pin is marked in yellow, meaning the function is not properly enabled 

Therefore, I checked the official Demo FW located in STM32Cube\Repository\STM32Cube_FW_H7_V1.13.0\Projects\STM32H735G-DK\Applications\LwIP\LwIP_TCP_Echo_Server\STM32CubeIDE, and even there, the pin is configured as GPIO_AF11_ETH.

 

I am curious why it was designed and developed this way when it only gets configured but doesn't actually function. Is it just missing from the ETH group in the CubeMX DB? Or is it originally an unsupported feature, but ended up like this because an existing circuit design was just recycled?

[waclawek.jan]

Now I’d like to add that I am not ST nor Synopsys insider and from the available documentation it’s not clear, if asserting ETH_MII_RX_ER signal at PB10, while the ETH MAC is configured in RMII mode, does or does not set the RE bit within the status bits of writeback Rx descriptor (in RDES0 in the original in ‘F4, in RDES3 in the newer one in ‘H7). It quite well may, and that can be established experimentally (although probably not at this board, as there’s no jumper at that signal to disconnect it and connect to a source of “manually” driven “disturbance”); now even if it does, whether it’s useful or not, is up to you to judge.

Oh, and I am by no means associated with CubeMX.

JW

[jmh8231]

That’s exactly why I wish this had been clearly stated in the documentation. Since the official development tools and the official board are designed in a way that contradicts each other, I hope ST will provide an official response soon. Almost all the information I can find on the forum regarding this is just unofficial “speculation” from people.

[everetcole]

It looks like a mismatch between the board design, CubeMX database, and the generated configuration. Since the official firmware still configures RMII_RX_ER as GPIO_AF11_ETH, I’d suspect the CubeMX pin definition or ETH peripheral metadata is incomplete rather than the board connection being accidental.

[jmh8231]

I agree. I wonder if that pin is missing from the CubeMX ETH group database... It would be great if we could get an official response.