some question about AD9361 fastlock

hi,

i am studying AD9361, and i want to realize the LO frequency sweep by using the fastlock mode.

But i have a problem with the picture below:

When i try to change LO frequency by the command :"echo 2 > out_altvoltage0_RX_LO_fastlock_recall",

the LO frequency didn't change as my expectation.

Wish someone would tell me why, thanks.