In `rtt_rosclock::rtt_now()` and `rtt_rosclock::rtt_wall_now()`:

I would suggest to use type `RTT::nsecs` here instead of `uint64_t`, which is the return type of `ticks2nsecs()` and resolves to `long long`. Furthermore `1E9` should be replaced by `1000000000ll` as constants in scientific notation are floating point constants, making the operations floating point instead of integer operations.