Power and cooling

There is no fan. Cooling means a slower clock and a dimmer backlight. Saving power uses the same two controls, plus a light-sleep recommendation when nothing is runnable.

kernel/power_governor.c is the only policy that changes them. Apps do not pick a megahertz. They publish how much compute they want, and the governor treats that as a ceiling.

Levels

The governor ranks whatever frequencies power_get_available_freqs() returns. It does not hardcode 240 MHz. On the host those are 240, 160, 80, 40, and 10. The ESP32-C6 boot path installs 160, 80, 40, 20, and 10.

Level	When	Clock	Backlight cap
Performance	A short burst, or an app that asked for HIGH	Highest	255
Balanced	Default interactive app	Middle	180
Economy	Idle, or the app asked for little work	Second lowest	64
Cool	The die is hot, or a task is burning CPU without having asked for HIGH	Lowest	16

One busy window steps up, so a tap still feels quick. Several quiet windows step down, so the clock does not flicker. A sustained full load with a hint below HIGH drops one level and stays there until the machine goes quiet. HIGH may keep the top clock.

Temperature, when a sensor answers, overrides everything. At 70 °C the level is Cool, including a refused HIGH request. It stays there until the die falls to 60 °C. No sample means the thermal rule stays off. The simulator has no die sensor.

What apps publish

APP_HELPER(clock_app, "clock",
    .demand = POWER_DEMAND_LOW,
    .every_ms = 100,
    .on_view = on_view);

Hint	Meaning
POWER_DEMAND_LOW	Timer, clock, sensor list. Cannot sit on the top clock.
POWER_DEMAND_NORMAL	Default interactive app.
POWER_DEMAND_HIGH	A game that may use the top clock until the die is hot.
POWER_DEMAND_IDLE	Nothing runnable should be doing work.

app_kit_set_demand() is the same hint for a screen that does not use APP_HELPER. Leaving the foreground puts that app's live hint back to NORMAL, so a game in the background does not keep the fast clock. Pomodoro, clock, and sensors publish LOW on the app task. A worker that must stay quiet calls power_set_demand() itself.

scheduler_step() never runs idle_task(). A step that finds only the idle task is an idle sample. scheduler_tick() closes a 100 ms window and calls power_governor_tick().

Light sleep, not deep sleep

When the level is Economy or Cool, nothing is runnable, and the next wake is at least 50 ms away, power_governor_light_sleep_ms() returns that gap. The governor does not call power_light_sleep(). On the host that function blocks on the wall clock. Deep sleep stays an explicit power_deep_sleep() call. It drops RAM and is still outside this policy.

Actuators

Tests install fakes with power_governor_set_actuators(). A NULL frequency callback uses power_set_cpu_freq(). A NULL temperature callback leaves the thermal rule off.

The simulator registers hal_display_set_backlight_cap(). That cap clamps later hal_display_set_brightness() calls. The ESP32-C6 backlight is on/off, so a non-zero cap leaves the panel on and only a zero cap blanks it.

ESP32-C6 boot (boards/esp32-c6-lcd/src_kernel/kernel_boot.cpp) registers hal_power_set_cpu_freq() and reads the die through the temp sensor the board config already owns. hal_power_get_die_temp_c() is the same reading for a caller that does not go through the sensor service. AVR and ESP8266 report no die temperature.