text: /* mbed Microcontroller Library
   * Copyright (c) 2006-2013 ARM Limited
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  #include <stddef.h>
  #include "us_ticker_api.h"
  #include "PeripheralNames.h"
  
  #define US_TICKER_TIMER      ((LPC_TIM_TypeDef *)LPC_TIM3_BASE)
  #define US_TICKER_TIMER_IRQn TIMER3_IRQn
  
  int us_ticker_inited = 0;
  
  void us_ticker_init(void) {
      if (us_ticker_inited) return;
      us_ticker_inited = 1;
      
      LPC_SC->PCONP |= 1 << 23; // Clock TIMER_3
      
      US_TICKER_TIMER->CTCR = 0x0; // timer mode
      uint32_t PCLK = PeripheralClock;
      
      US_TICKER_TIMER->TCR = 0x2;  // reset
      
      uint32_t prescale = PCLK / 1000000; // default to 1MHz (1 us ticks)
      US_TICKER_TIMER->PR = prescale - 1;
      US_TICKER_TIMER->TCR = 1; // enable = 1, reset = 0
      
      NVIC_SetVector(US_TICKER_TIMER_IRQn, (uint32_t)us_ticker_irq_handler);
      NVIC_EnableIRQ(US_TICKER_TIMER_IRQn);
  }
  
  uint32_t us_ticker_read() {
      if (!us_ticker_inited)
          us_ticker_init();
      
      return US_TICKER_TIMER->TC;
  }
  
  void us_ticker_set_interrupt(unsigned int timestamp) {
      // set match value
      US_TICKER_TIMER->MR0 = timestamp;
      // enable match interrupt
      US_TICKER_TIMER->MCR |= 1;
  }
  
  void us_ticker_disable_interrupt(void) {
      US_TICKER_TIMER->MCR &= ~1;
  }
  
  void us_ticker_clear_interrupt(void) {
      US_TICKER_TIMER->IR = 1;
  }
  