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AM625: Which register to configure RMII_REF_CLK src?

Part Number: AM625

#1. From the description, there should be a register to configure the RMII_REF_CLK source, which one is it?

#2. How to configure rmii-clock-ext in dts file?

  • Schulyer,

    would you help?

  • Is there such a configurable option? 

  • If you look at the "12.3.1.2.1 CPSW0 RMII Interface" chapter in the AM62x TRM it seems that the only difference between "internal clock source" and "external clock source" is that in the "internal" case the clocks comes from CLKOUT0 whereas in the "external" case it comes from "somewhere else" (ext. oscillator or PHY). From the CPSW's point of view it is always external.

    If you further look at the Boot Modes chapter on Ethernet in "Table 5-22. Ethernet RMII Clocking" you see that the only valid configurations have BOOTMODE Pin 8 as '0' (external clock source). The two encodings with BOOTMODE Pin 8 as '1' are "Not a valid configuration". Either RMII1_REF_CLK is driven from "somewhere else" or from CLKOUT0.

    I'm pretty sure that at the CPSW / RMII1_REF_CLK level there are only external clocks, and the pin is input only (also supported by the datasheet, which says RMII Reference Clock is input only). The only question is whether CLKOUT0 gets enabled to drive the 50 MHz clock or not.

    Your colleagues might of course have a different answer.

    Regards,

    Dominic

  • Thanks Dominic,

    So actually only BOOTMODE_9 effect to enable CLKOUT0 output or not.