Tune time

Hi,

Just a few general querys…

How long does it take for an RFX card to tune and lock to a frequency,
once a set_freq command is issued?
Does it matter if the steps are small or large, ie a greater swing on
the VCO?
Is there a way to tell if/when the VCO is locked, ie its tuned (could I
monitor it via the fpga gpio)?
Is there a way to tell if the frequency reference is locked to an
external reference (could I monitor it via the fpga gpio)?

Regards,
Dave