nx_energy_probe.nx

nx_energy_probe.nx -- REAL-hardware energy probe, HARDWARE-AGNOSTIC. The gate-activity model (nx_gate_energy) gives a PORTABLE energy currency that runs on any hardware. This probe is the other half: read the REAL energy the NODE actually burns, using whatever sensor THIS silicon exposes, and degrade gracefully when none exists -- never fabricating a joule we didn't measure. Source priority (best real measurement first), detected at runtime: RAPL -- x86 package energy counter via /sys (microjoules, accumulating). Real. PSU -- battery fuel-gauge. The GARDEN-SENSOR / laptop-on-battery case. HONEST RULE: a battery only attributes the CPU's energy while DISCHARGING -- on AC the wall adapter powers the CPU and the pack charges separately, so a charging battery CANNOT measure the workload. And energy_now is uWh-coarse (a short workload moves it by 0), so we integrate instantaneous power_now (uW) x measured time (us) -> real microjoules. I2C -- an INA219/INA260 current-sense chip on an I2C bus (/dev/i2c-*): the canonical embedded power sensor. Detected; the INA219 register read streams in as a later SEED piece (honest: not faked here). CYCLE -- rdtsc/rdcycle: ALWAYS available, every target (the compiler lowers __rdtsc to rdcycle on RV64/ARM). NOT a sad fallback: the cycle COUNT is itself CHARGE-INDEPENDENT, and nx_energy_model turns it into real joules via a calibrated fJ/cycle -> energy is measurable in ANY power state. IMPORTANT (operator: "only measuring when not charging is not S-class"): the S-class path does NOT depend on the battery. RAPL and an INA219 rail sensor are state-independent; nx_energy_model + nx_perf_counters give real joules from charge-independent activity counters (cycles/instructions) on ANY node in ANY power state. The battery-discharge path is only a calibration source, demoted below the state-independent ones. Cardinal #14: a missing sensor is never a failure -- fall through to the universal charge-independent estimator. CITATIONS (real): RAPL -- Intel SDM Vol.3B; Khan et al., ACM TOMPECS 2018. Battery -- Linux power_supply class (Documentation/power/power_supply_class.rst, GPL). Rail sensor -- TI INA219 datasheet (SBOS448). Activity->energy -- Horowitz, ISSCC 2014; Bircher & John, ISPASS 2007.