#define SKIP_COUNTER_MAX 10000
#define VOLUMES_MAX_INDEX 20
#define VOLUMES_MIN_INDEX 0

int volumes_left[] = {2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 7, 7, 7, 8, 8, 8, 8, 8, 8};

int volumes_right[] = {8, 8, 8, 8, 8, 8, 7, 7, 7, 6, 6, 5, 5, 5, 4, 4, 4, 3, 3, 3, 2};

enum direction
{
  left,
  right
};

enum direction current_direction = right;

int skip_counter = 0;

int current_index = 10;

void process_signal(void)
{
  skip_counter++;

  if (skip_counter >= SKIP_COUNTER_MAX)
  {
    skip_counter = 0;

    if (current_direction == right)
    {
      current_index++;
      if (current_index == VOLUMES_MAX_INDEX)
      {
        current_direction = left;
      }
    }
    else
    {
      current_index--;
      if (current_index == VOLUMES_MIN_INDEX)
      {
        current_direction = right;
      }
    }
  }

  iChannel0LeftOut = ((iChannel0LeftIn << 8) >> (8 - volumes_left[current_index])) >> 8;
  iChannel0RightOut = ((iChannel0RightIn << 8) >> (8 - volumes_right[current_index])) >> 8;
}