Cintro doesn't work on 3.90 because the autoboot function is broken on all custom firmwares after 3.52..
I thought I had saw a cintro thingy for 3.80m33 :s
nope! like i said the autoboot function has been broken since 3.52 so Cintro won't work on any firmware after that...well, until the autoboot function is fixed anyway