KV58: is RMII clock supported on ENET_1588_CLKIN

[iainristmt]

I want to run my microcontroller with the system clock derived from EXTAL and the RMII clock sourced from ENET_1588_CLKIN. I cannot run with a 50 MHz clock attached to EXTAL due to system requirements.

The KV58 reference manual inlcludes the following contradictory statements:

1. RMII clock source is tied to EXTAL:
   • Section 51.1.2 states that RMII_REF_CLK is internally tied to EXTAL.
2. RMII clock source is configurable:
   • Section 6.5.9 and Table 11-26 state that the RMII clock source can be EXTAL or ENET_1588_CLKIN, selected via SIM_SOPT2[RMIISRC].

Which one is it? Can I have the microcontroller system clock derived from EXTAL and have the RMII clock sourced from a 50 MHz clock attached to ENET_1588_CLKIN?

[imferreira]

Hello,

Is there any update to clarify this contradiction on the reference manual?

1. RMII clock source is tied to EXTAL:
   • Section 51.1.2 states that RMII_REF_CLK is internally tied to EXTAL.
2. RMII clock source is configurable:
   • Section 6.5.9 and Table 11-26 state that the RMII clock source can be EXTAL or ENET_1588_CLKIN, selected via SIM_SOPT2[RMIISRC].

I am also trying to use RMII interface clock sourced from ENET_1588_CLKIN and having issues to make works properly, then I found this contradiction on the documentation and I am wondering if it might be the cause. 

Thanks,

[Robin_Shen]

Hi Iain Rist,

The 50MHz external clock source can be connect to EXTAL pin.(The 48MHz allowable maximum clock of this source is a mistake in datasheet.)
You can refer the input clock circuit on TWR-KV58F220M:

I am not sure if the "Section 51.1.2 states that RMII_REF_CLK is internally tied to EXTAL." is documentation error or not.
Experiments may be needed to verify feasibility.
First select PTE26 to ENET_1588_CLKIN function via PORTE_PCR26[MUX].
Then select ENET_1588_CLKIN via SIM_SOPT2[RMIISRC].
Check whether the ENET_1588_CLKIN from PTE26 is able to clock RMII.

Best Regards,

Robin

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