Power save
Cut idle power with one build flag: power_save turns on automatic light sleep, so an event-driven device sleeps between events for free — plus power_hold() for the rare stretch that must stay awake.
Automatic light sleep — free, nothing to call
The light sleep is already in the firmware: in the event-driven model the reactor sleeps on its own between one event and the next, free, without you calling anything. Turn it on with one line in php-baremetal.config.toml:
power_save = trueThis enables esp_pm tickless idle. Whenever the reactor is idle — blocked waiting for the next event — the chip drops into light sleep by itself: RAM is retained and it wakes instantly on the next timer, GPIO or request. No sleep code in your PHP.
On a bare ESP32-S3-Zero, a script with one heartbeat every 10 s idled at ~0.95 mA (from ~49 mA active) — about a 50x drop — measured on external 5 V.
This pairs naturally with the event-driven model: the more your device waits on events instead of looping, the more of the time it spends asleep.
Staying awake when it matters
For a short time-critical stretch, forbid light sleep around it:
power_hold(); // no light sleep from here
// ... time-critical work ...
power_release(); // allow it againpower_hold() can nest; each call needs a matching power_release(). As a safety net, the reactor auto-releases any hold still standing at the end of each event handler, so a forgotten power_release() can't pin the chip awake forever.
What doesn't mix with power_save
An I2cBus::CORE1 bus is rejected under power_save (the constructor throws): its core-1 polling loop keeps the CPU busy and would defeat light sleep. Use the default I2cBus::SYNC instead.
Measuring it
Put a current meter inline on the supply and expect a low idle current, with a step up during any power_hold() window.
Measure from external 5 V, not over USB
With the USB data cable attached, the USB-Serial/JTAG driver can hold a power-management lock that keeps the chip from actually entering light sleep, so the idle current may not drop. For a clean reading, power the board from 5 V externally with the USB data cable disconnected.
Explicit sleep (deep sleep)
Explicit light_sleep() / deep_sleep() calls are not built into the firmware. With power_save you rarely need an explicit light sleep. Deep sleep tears everything down and depends on the board's wake topology (which pin wakes it, pull-ups, state saved to NVS to resume), so for now it lives as a small per-project C extension you can copy and adapt — see the power-bench example. The power-save example shows the automatic path.