usertools ui_led_example4 explained -- part1

ui_led_example4--p1.cpp

#include <ui.h>           // include protothread library

#define LEDPIN 13  // LEDPIN is a constant 

uint16_t sub_time = 0;  // subtracts time from LED periods

void toggleLED() {
  boolean ledstate = digitalRead(LEDPIN); // get LED state
  ledstate ^= 1;   // toggle LED state using xor
  digitalWrite(LEDPIN, ledstate); // write inversed state back
}

/* This function toggles the LED after 'interval' ms passed */
PT_THREAD blinky_thread(pthread *pt) {
  // Notice that this function doesn't require any static integers. Everything
  // is stored inside of pt.
  PT_BEGIN(pt);
  while(1) {
    //* Use PT_WAIT_MS instead of the timestamp, etc.
    PT_WAIT_MS(pt, pt->get_int_input(0) - sub_time); // macro to do "wait for milliseconds"
    toggleLED();
  }
  PT_END(pt);
}