How to Use Timers

There are two classes for timers in package pollen.time. The TimerManager class handles administration and registration of timers. It is usually not necessary for a timer client to access this class. Timer clients can use the timer subsystem via the Timer class.

Here is a simple example that allocates a Timer with a handler and starts it. When the timer ticks, the code toggles an led.

import pollen.environment as Env
from Env import Led

from pollen.time import Timer

module TimerBlink {

  host new Timer t1(tick)    // Declare and allocate a Timer with a tick() handler

  tick() {
    Led.toggle()
  }

  pollen.run() {
    t1.start(500, true)      // Start the timer
    Env.Newsroom.run()
  }
}

The Timer class is located in the pollen-core bundle and you can download it. It is very simple to use.

1. Define a handler for the timer. This handler will define what you want to happen when the timer ticks a specified number of times. In the code above the handler is tick().

2. Declare and initialize a host Timer. In this example the host timer is called t1 and it is initialized with tick() as its handler.

3. Start the timer by calling start(). The first parameter specifies the timer interval in milliseconds and the second is a boolean which controls whether this interval will repeat. In this code the start method is called in pollen.run() which is the main entry function (like main in C).

To stop the timer stop() can be called.

To translate this code an environment must be chosen. You can do this on the command line. There are environments that are available in the pollen-core cloud bundle or you can define your own. The -e option below selects the Arduino Uno environment. All the bundles specified below are cloud bundles as indicated by the @ preceding the bundle name but you can define your own locally. (Or you can download and modify these). The -t option specifies the tool chain. This command line will invoke the avr-gcc compiler on the code.

pollenc    		                        \
    -o <output path>		            \
    -t avr-gcc --mcu atmega328p 		\
    -b @pollen-core 		            \
    -b @atmel 		                    \
    -b @environments 		            \
    -e @environments/arduino/Uno 		\
    TimerBlink.p