Is it possible to count pulses with the 51822 from an external device in the range of 250-15.000 pulses pr. second, while the CPU is powered down (softdevice sleep)?
I've had a look at the pwm_analyzer sample, which might do the trick. But I'm not familiar with all the GPIOTE events and tasks. and I'm a little unsure that the resolution is high enough for this purpose. As far as I can tell the example measures both the low and high duty cycles, and firing an interrupt after right after it has measured the high cycle.
I'm not particular interested in generating an interrupt for this reading, as I would rather read the results while the BLE stack is executing to avoid extra wake-up cycles. But according to the example, it seems there is no specific code that restarts the events/task. So I guess it means that they will continuously provide the result to the registers.
Am I totally off here or is there an easier way to simply count the number of pulses from an external device?
Looking at the Timer description in the reference manual, it can also operate in a counter mode triggered by a COUNT task. Is it possible to setup a GPIO pin to trigger that task by a lo-hi transition? This way I can simply read the register whenever the SD is awake and do the frequency calculation based on the time elapsed since last read.