Timer — `pymcu.hal.timer`#

from pymcu.hal.timer import Timer

Hardware timer configuration. Wraps Timer/Counter 0, 1, and 2 on ATmega328P.

class `Timer`#

`Timer(n: uint8, prescaler: uint16)`#

Configures a hardware timer. n selects the timer (0, 1, or 2).

Prescaler	Divisor	Period per tick (16 MHz)
1	/1	62.5 ns
8	/8	500 ns
64	/64	4 µs
256	/256	16 µs
1024	/1024	64 µs

Methods#

Method	Description
`start()`	Enable the timer
`stop()`	Disable the timer (prescaler = 0)
`clear()`	Reset TCNT to 0
`set_compare(val: uint8)`	Set OCR register + enable CTC mode

Examples#

Overflow interrupt (periodic task)#

from pymcu.hal.timer import Timer
from pymcu.types import uint8, ptr

TIMSK0: ptr[uint8] = ptr(0x6E)

tick: uint8 = 0

@interrupt(0x0020)    # Timer0 OVF vector (ATmega328P)
def on_timer0_ovf():
    global tick
    tick += 1

def main():
    t = Timer(0, 64)
    TIMSK0[1] = 1     # enable TOIE0 (Timer0 Overflow Interrupt)
    t.start()
    # sei emitted automatically because @interrupt handler is registered
    while True:
        pass

CTC mode (precise frequency)#

from pymcu.hal.timer import Timer
from pymcu.types import uint8, ptr

TIMSK1: ptr[uint8] = ptr(0x6F)

@interrupt(0x0018)    # Timer1 COMPA vector
def on_compare():
    pass              # fires at exactly 1 kHz (16 MHz / 64 / 250)

def main():
    t = Timer(1, 64)
    t.set_compare(250)        # OCR1A = 250; CTC mode
    TIMSK1[1] = 1             # enable OCIE1A
    t.start()
    while True:
        pass

Timer0 register map (ATmega328P)#

Register	Address	Description
`TCCR0A`	`0x44`	Waveform generation mode
`TCCR0B`	`0x45`	Clock select (prescaler)
`TCNT0`	`0x46`	Counter value
`OCR0A`	`0x47`	Output Compare A
`OCR0B`	`0x48`	Output Compare B
`TIMSK0`	`0x6E`	Interrupt mask (TOIE0, OCIE0A, OCIE0B)
`TIFR0`	`0x35`	Interrupt flag register