Micropython Concurrency: Mastering Timers and Interrupts

Micropython Concurrency: Mastering Timers and Interrupts

Concurrency in Micropython, especially on resource-constrained microcontrollers, can be a powerful tool. While true threading isn’t directly supported, Micropython offers clever alternatives: Timers and Interrupts. Let’s explore how to leverage them effectively.

Understanding the Basics

• Timers: Think of timers as scheduled events. You program them to trigger a function call after a specific time interval or at a predefined frequency. This is excellent for tasks like periodic sensor readings or controlling actuators.
• Interrupts: Interrupts are event-driven. They sit dormant until a specific hardware event occurs – a button press, a sensor threshold, etc. This makes them ideal for real-time responsiveness.

Working with Timers

1. Initialization: Begin by importing the machine module and creating a Timer object. Micropython usually provides multiple timer channels (Timer0, Timer1, etc.).

import machine

timer = machine.Timer(0) 

2. Callback Function: Define a function that will be executed when the timer triggers.

def timer_callback(timer):
    print("Timer Event!")

3. Configuration: Use the init() method to configure the timer mode and link your callback function.

   • period: Time in milliseconds between events (for periodic timers)
   • mode: machine.Timer.ONE_SHOT for a single event, machine.Timer.PERIODIC for recurring events

timer.init(period=1000, mode=machine.Timer.PERIODIC, callback=timer_callback)  

Handling Interrupts

1. Pin Setup: Configure the GPIO pin where you expect the interrupt.

pin = machine.Pin(12, machine.Pin.IN, machine.Pin.PULL_UP)

2. Interrupt Handler: Write a function to process the interrupt. Keep it short and efficient.

def interrupt_handler(pin):
    print("Button Pressed!")

3. Attaching the Interrupt: Use the irq() method to associate the interrupt handler with the pin.

   • trigger: Specify the trigger condition (e.g., machine.Pin.IRQ_FALLING for a button press on a pull-up resistor)

pin.irq(trigger=machine.Pin.IRQ_FALLING, handler=interrupt_handler)

Pro Tips:

• Non-Blocking Code: Both timer callbacks and interrupt handlers should execute quickly to avoid blocking the main Micropython thread. For longer operations, consider using flags or queues to signal the main thread.
• Debouncing: Hardware can produce noisy signals. Implement debouncing techniques, especially for button interrupts, to prevent multiple spurious triggers.

Tags: Micropython, Concurrency, Timers, Interrupts, Embedded Systems, Hardware, Real-time