AXP 209 PMU - Sampling frequency and power profiling

AFAIK, from last year, there are some new driver for AXP209/202 PMU for mainline kernel. One of the main new features that i really like is custom sampling frequency compared to the original driver for linux kernel 3.4 (i just remember the interval are 2 seconds).

I want to use AXP209 PMU for power/energy profiling and consumption study of some SBC such as Banana Pi/Pro and some other Allwinner based SBC as comparison. The question is

1. How i want to know current sampling frequency from PMU and how to change the frequency? (25, 50,  100 or 200Hz)
2. What is the reasonable/best practice to write the captured power consumption value (with timestamp) into some logfile or send it through serial communication? if possible without effecting the power consumption itself? I tried AXP209 driver for linux kernel 3.4 and using i2c command to write the captured power consumption value into logfile but it seem the process itself consumed a lot of power.

p/s - I don't have professional electric/electronic background. I just learn it from internet.