> I meet a problem of interface converter listed as below.

RMII uses the same bit order (transmission order, little) as MII. It
orders it's 2bit-words in the same order as MII order it's 4bit-words
(nibbles).

Basically RMII is just the same as MII but smaller words.

The spec:s of your RMII-interface most likely describes this bit-order in
detail.

I could dig up some VHDL models of RMII from an academic project. That
project never flew on RMII, so the RMII-model is not verified against the
real world.

Regards,
Peter