On Mon, 23 Oct 2023 10:41:50 +0200, Oleksij Rempel wrote: > Here is KSZ8873 as initial reference: > https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/00002348A.pdf > 3.3.9 RMII INTERFACE OPERATION: > "When EN_REFCLKO_3 is high, KSZ8873RLL will output a 50 MHz in REFCLKO_3. > Register 198 bit[3] is used to select internal or external reference > clock. Internal reference clock means that the clock for the RMII of > KSZ8873RLL will be provided by the KSZ8873RLL internally and the > REFCLKI_3 pin is unconnected. For the external reference clock, the > clock will provide to KSZ8873RLL via REFCLKI_3." > > KSZ9897: > http://ww1.microchip.com/downloads/en/DeviceDoc/00002330B.pdf > 4.11.2 REDUCED MEDIA INDEPENDENT INTERFACE (RMII) The upper paragraph refers to the case when switch is acting as a clock provider (regardless whether its set as internal or external reference clock). You can see this if you look at the next paragraph: "If KSZ8863RLL does not provide the reference clock, this 50 MHz reference clock with divide-by-2 (25 MHz) has to be used in X1 pin instead of the 25 MHz crystal, since the ..." So rmii-clk-internal property does not select whether switch is acting as a clock provider or clock consumer which is what you are refering to I believe? The clock provider/consumer is set via strapping pins. Real case scenario: I have a board where switch is acting as a clock provider, generating output to REFCLKO pin and feeding it to uC. This board does not have externally routed copper track from REFCLKO to REFCLKI, thus making the RMII interface not operable, unless the rmii-clk-internal bit is set. If this bit is not set, only way to make it running is to solder a jumper wire from REFCLKO to REFCLKI.
