"Throughout the test, the Arm Cortex-M0+ processor drew an average current from the compact Al-BPV of 1.4±0.4 μA with a voltage of 0.72±0.14 V. ... As the average power drawn from the compact Al-BPV during the 27 weeks of experimental run (1.05 μW) was larger than the minimum power required to run the CPU (i.e., 0.3 μW), it is likely that a smaller power-generating system could be used, or that more computationally intensive algorithms could be performed."
and:
"We programmed the Cortex-M0+ CPU to calculate a sum of consecutive integers as an example compute workload, and assess the correctness of the computation by verifying the sum against a precomputed value."
Pretty neat -- although it looks like they were clocking the chip at only 10 KHz.