NimBLE controller: timer mapping for nrf51

[Hauke Petersen]

Dear community,

I am not fully confident, if this is the right place to ask, so let me 
know if there is a better place :-)

We were recently trying to run the NimBLE controller on nrf51-based 
platforms using RIOT. We found that that the NimBLE controller has a 
hardcoded dependency on the nrf51 NRF_TIMER0. The same timer is per 
default also used as base for the RIOT system timer (xtimer). Although 
its a simple workaround to map RIOT to use some other timer, it is 
sub-optimal in terms of energy usage, as the other timers are all only 
16-bit. So my question: does the NimBLE controller need a >16-bit timer, 
and would it be feasible to make the used hw-timer configurable for the 
NimBLE nrf51-related controller code?

Cheers,
Hauke