Separate an RTC alarm match from an asserted interrupt pin and a successful host wake. On the NXP PCF8523, a latched alarm flag can coexist with disabled alarm output or a pin still configured as CLKOUT. A later read showing that time passed the alarm is not evidence that the sleeping host received a usable…
A failed suspend attempt needs two kinds of recovery: the failing callback must undo its own partial changes, and the power-management core must unwind phases that other devices completed successfully. Do not assume that returning an error automatically schedules the matching resume callback for the failed phase. Applicability: this article pins Linux v6.12 system suspend…
Assign each pin a sleep role before changing its configuration. A wake input must retain a working input path and a defined inactive level, while an unused input may benefit from disconnecting its input buffer. Applying the same low-power setting to both can produce a quiet board that cannot wake. Applicability: the concrete example uses…
Give every latency-sensitive operation an explicit PM QoS owner and remove its request when that operation finishes. The effective CPU latency constraint is aggregated across owners, so closing one application’s request need not relax the system. Diagnose the surviving owner before changing idle-state policy globally. Applicability: this article pins Linux v6.12 with CONFIG_CPU_IDLE and the…
Divide the energy consumed over a defined workload by the number of results that actually satisfy the product’s acceptance rules. Include failed attempts, retries, wake overhead, and idle time in the numerator. Counting every conversion or transmitted packet as a useful result can make an unreliable low-power policy look efficient. Applicability: this is an original…
A cold battery can retain useful charge yet fail to keep a product above its minimum voltage during a short load pulse. Treat remaining charge and peak-load voltage as separate qualification questions. Measure the cell and the product rail under the actual pulse sequence, with temperature and discharge history controlled. Applicability: the concrete cell is…
A board that boots from a generous bench supply but repeatedly restarts from its intended source may be demanding more startup current than that source can deliver while maintaining voltage. Capture the input ramp, downstream rail, current-limit state, and first boot activity. Separate charging the board’s capacitance from powering the load that starts while that…
A reboot near radio transmission is not enough to diagnose brownout. Capture the voltage at the MCU supply, a trustworthy load-activity marker, and evidence of a new boot on one timeline. Then interpret the earliest reset status using the selected device’s rules. A stable bench-supply display and an empty crash log cannot exclude a short…
A disabled supply can still receive current through a signal connection from an energized domain. Diagnose that path by mapping every crossing signal, observing the supposedly off rail, and removing or changing one supported source at a time. A regulator-disable success and a GPIO configured as input do not establish electrical isolation. Applicability: this is…
Choose a current instrument by the smallest idle signal, largest burst, transition speed, and permitted disturbance to the supply. Then verify that the recorded data preserves charge across range changes. A readable low-current display does not prove that short bursts are captured, and a flattened peak does not automatically mean its energy was lost. Applicability:…