text: /*
   * This file is part of the MicroPython project, http://micropython.org/
   *
   * The MIT License (MIT)
   *
   * Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  
  #include "tick.h"
  
  #include "supervisor/shared/autoreload.h"
  #include "shared-module/gamepad/__init__.h"
  #include "shared-bindings/microcontroller/Processor.h"
  #include "nrf.h"
  
  // Global millisecond tick count
  volatile uint64_t ticks_ms = 0;
  
  void SysTick_Handler(void) {
      // SysTick interrupt handler called when the SysTick timer reaches zero
      // (every millisecond).
      ticks_ms += 1;
  
      #ifdef CIRCUITPY_AUTORELOAD_DELAY_MS
          autoreload_tick();
      #endif
      #ifdef CIRCUITPY_GAMEPAD_TICKS
      if (!(ticks_ms & CIRCUITPY_GAMEPAD_TICKS)) {
          gamepad_tick();
      }
      #endif
  }
  
  void tick_init() {
      uint32_t ticks_per_ms = common_hal_mcu_processor_get_frequency() / 1000;
      SysTick_Config(ticks_per_ms); // interrupt is enabled
  }
  
  void tick_delay(uint32_t us) {
      uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
      uint32_t us_between_ticks = SysTick->VAL / ticks_per_us;
      uint64_t start_ms = ticks_ms;
      while (us > 1000) {
          while (ticks_ms == start_ms) {}
          us -= us_between_ticks;
          start_ms = ticks_ms;
          us_between_ticks = 1000;
      }
      while (SysTick->VAL > ((us_between_ticks - us) * ticks_per_us)) {}
  }
  
  // us counts down!
  void current_tick(uint64_t* ms, uint32_t* us_until_ms) {
      uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
      *ms = ticks_ms;
      *us_until_ms = SysTick->VAL / ticks_per_us;
  }
  
  void wait_until(uint64_t ms, uint32_t us_until_ms) {
      uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
      while(ticks_ms <= ms && SysTick->VAL / ticks_per_us >= us_until_ms) {}
  }
  