def packet_lengths=(len)
      ptr = @ptr + Call::Transfer.size
      num_packets.times do
        ptr.write_uint(len)
        ptr += Call::IsoPacketDescriptor.size
      end
    end
def packet_lengths=(len)
      ptr = @ptr + Call::Transfer.size
      num_packets.times do
        ptr.write_uint(len)
        ptr += Call::IsoPacketDescriptor.size
      end
    end
Convenience function to set the length of all packets in an
 isochronous transfer, based on {IsochronousTransfer#num_packets}.