code: func (c *Adaptor) GetSpiConnection(busNum, chipNum, mode, bits int, maxSpeed int64) (connection spi.Connection, err error) {
  	c.mutex.Lock()
  	defer c.mutex.Unlock()
  
  	if (busNum < 0) || (busNum > 1) {
  		return nil, fmt.Errorf("Bus number %d out of range", busNum)
  	}
  
  	if c.spiBuses[busNum] == nil {
  		c.spiBuses[busNum], err = spi.GetSpiConnection(busNum, chipNum, mode, bits, maxSpeed)
  	}
  
  	return c.spiBuses[busNum], err
  }
docs: // GetSpiConnection returns an spi connection to a device on a specified bus.
  // Valid bus number is [0..1] which corresponds to /dev/spidev0.0 through /dev/spidev0.1.