Comment by Karliss

From what I understand the timer registers should be on APB(1) bus which operates at fixed 26MHz clock. That should be much closer to the scale of fast timer clocks compared to cpu_relax() and main CPU clock running somewhere in the range of 0.5-1GHz and potentially doing some dynamic frequency scaling for power saving purpose.

The silliest part of this mess is that 26Mhz clock for APB1 bus is derived from the same source as 13Mhz, 6.5Mhz 3.25Mhz, 1Mhz clocks usable by fast timers.