空気にタッチ：簡単なジェスチャによる機器のウェイクアップ

__interrupt void TimedInterrupt( void ) 
{

  uint8 proximity_counts;
  ....
  .... 


  if ( device_status == SLEEP_MODE )
  {
    // read one byte from register 0x16
    proximity_counts = read_i2c_register(MAX44000_ADDR,0x16,1);
    if (proximity_counts > WAKEUP_THRESHOLD)
    {
      device_status = WAKE_MODE;
      ...
    }
    else
    {
      // do whatever it is you need to in sleep mode
      ...
      ...
    }
  }

  ...
  ...

}

// example interrupt function where this might be implemented
__interrupt void TimedInterrupt( void ) 
{

  uint8 proximity_counts;
  uint8 filtered_counts;
  ....
  .... 


  if ( device_status == SLEEP_MODE )
  {
    // read one byte from register 0x16
    proximity_counts = read_i2c_register(MAX44000_ADDR,0x16,1);

    // weights[QUEUE_SIZE] contains the filter weights for the FIR filter
    // data_queue[QUEUE_SIZE] is a FIFO queue meant to be the input to the filter
    filtered_counts = fir_filter(proximity_counts,weights,data_queue);
    
    if (filtered_counts > WAKEUP_THRESHOLD)
    {
      device_status = WAKE_MODE;
      ...
    }
    else
    {
      // do whatever it is you need to in sleep mode
      ...
      ...
    }
  }

  ...
  ...

}

/**
 * fir_filter()
 *
 * Implements an FIR filter in the form
 *   y = w[0]*x[0] + w[1]*x[1] + ... + w[QUEUE_SIZE]*x[QUEUE_SIZE]
 *
 * Arguments:
 *	uint8 input - newest datapoint taken (that is, x[0])
 *	uint8 *weights - w[0]...w[QUEUE_SIZE]
 *	uint8 *queue - the discrete sequence x[0]...x[QUEUE_SIZE]
 * 
 * Returns: 
 *	The FIR-filtered output, y
 */
uint8 fir_filter(uint8 input, uint8 *weights, uint8 *queue)
{

  uint8 i;
  int sum = 0;

  // pop first entry in the queue, then
  // push new data into the last position
  push_into_queue(queue,input);

  // input is now x[0]
  for (i=0; i<QUEUE_SIZE; ++i)
  {
    sum += weights[i]*queue[i];
  }

  return (sum/QUEUE_SIZE);
}

// this handles hardware-level interrupts on the micro
__interrupt void irq_handler( void )
{
  ...
  
  // if the hardware interrupt came from the MAX44000 sensor
  // pulling its \INT pin low
  if ( irq_source == MAX44000 )
  {
    // if the device is in sleep mode
    if (device_status == SLEEP_MODE)
    {
      device_status = WAKE_MODE;	// wake up the device
      ...
      // reconfigure whatever else you need here as the system wakes up
    }
    // otherwise, handle it however it is you wish
    else
    {
      ...
    }
  }
  
  ...
}

/**
 *	configure_max44000_for_sleep_mode()
 *
 *	Sets up the MAX44000 to trigger a hardware interrupt when the proximity
 *	counts go above some set threshold.
 *
 *	Arguments:
 *		uint8 upper_threshold - the set threshold (8-bit mode)
 *
 *	Returns:
 *		n/a
 */
void configure_max44000_for_sleep_mode(uint8 upper_threshold)
{
  uint8 max44000_thresh_registers[] = {0x0B,0x0C};
  uint8 max44000_upper_thresh[] = {0x40,0};
  
  max44000_upper_thresh[1] = upper_threshold;
  
  // do a consecutive write of 0 followed by upper_threshold to 
  // registers 0xB and 0xC, respectively
  //	MAX44000_ADDR is usually 0x94
  // interrupt will trigger only if proximity value is above the threshold
  write_i2c_register(MAX44000_ADDR,max44000_thresh_registers,
				max44000_upper_thresh,2);
				
  
  // write to bits 2 and 3 of register 0x0A here if you wish to set the
  // persist time to anything other than one sample
  
  // writes to register 0x01 to enable interrupts on the MAX44000
  max44000_enable_interrupt();
  
  return;
}