Sleep / Power — `pymcu.hal.power`#

from pymcu.hal.power import sleep_power_down

Sleep mode helpers that halt the CPU and reduce current consumption. Returning from any sleep_* function means the MCU has woken from sleep.

Warning

Interrupts must be enabled Global interrupts (sei) must be enabled before calling any sleep function, or the MCU will sleep indefinitely. The compiler emits sei automatically when at least one @interrupt handler is registered; otherwise call asm("sei") explicitly.

Sleep modes#

Function	Typical current (3 V, 25 °C)	Wake sources
`sleep_idle()`	~6 mA	All interrupts
`sleep_adc_noise()`	~1 mA	ADC complete, ext-int, TWI address match, Timer2
`sleep_power_down()`	~0.1 µA	External INT0/INT1, TWI address match, WDT
`sleep_power_save()`	~0.1 µA	Same as power-down + Timer2 async
`sleep_standby()`	~0.1 µA	Same as power-down (faster oscillator startup)

Examples#

Power-down on button press#

from pymcu.hal.gpio import Pin
from pymcu.hal.power import sleep_power_down
from pymcu.types import uint8, ptr

EICRA: ptr[uint8] = ptr(0x69)
EIMSK: ptr[uint8] = ptr(0x3D)

led = Pin("PB5", Pin.OUT)

@interrupt(0x0002)    # INT0 vector (ATmega328P)
def on_int0():
    led.toggle()

def main():
    EICRA[0] = 0    # INT0 triggered on low level
    EIMSK[0] = 1    # enable INT0
    asm("sei")
    while True:
        sleep_power_down()   # wake on INT0, toggle LED, sleep again

ADC noise reduction sleep#

from pymcu.hal.adc import AnalogPin
from pymcu.hal.power import sleep_adc_noise
from pymcu.types import uint16

sensor = AnalogPin("A0")

def read_quiet() -> uint16:
    sensor.start()
    sleep_adc_noise()    # CPU sleeps; ADC completes, ADC ISR wakes CPU
    return sensor.value()

Watchdog-based periodic wake (~0.1 µA between wakes)#

from pymcu.hal.power import sleep_power_down
from pymcu.hal.watchdog import Watchdog

wdt = Watchdog(timeout_ms=1000)

@interrupt(0x0018)    # WDT vector
def on_wdt():
    pass

def main():
    wdt.enable()
    asm("sei")
    while True:
        sleep_power_down()
        do_periodic_task()

ATmega328P register map#

Register	Address	Description
`SMCR`	`0x53`	Sleep Mode Control Register (SM2:0, SE)
`MCUCR`	`0x55`	MCU Control Register (BODS, BODSE)