beaglebone cape universal anf u-boot falcon mode

Hi all,

I’m trying to boot bealgebone with u-boot in falcon mode but I don’t know how to enable cape universal in order to use the beaglebone uarts.
I’m useìing the Robert Nelson kernel 4.14.87-bone-rt-r17 and I tried to pass “cape_universal=1” as kernel args but it doesn’t work.

can someone give me a suggestion on how to do it?