code: func (node *ClientNode) recalcBV(now mclock.AbsTime) {
  	dt := uint64(now - node.lastTime)
  	if now < node.lastTime {
  		dt = 0
  	}
  	node.bufValue += node.params.MinRecharge * dt / uint64(fcTimeConst)
  	if node.bufValue > node.params.BufLimit {
  		node.bufValue = node.params.BufLimit
  	}
  	if node.log != nil {
  		node.log.add(now, fmt.Sprintf("updated  bv=%d  MRR=%d  BufLimit=%d", node.bufValue, node.params.MinRecharge, node.params.BufLimit))
  	}
  	node.lastTime = now
  }
docs: // recalcBV recalculates the buffer value at a specified time