tx_cont random data

In the wl1271 calibrator tx_cont mode, you can select the packet content, as described in the README:

  Type is 0-data packet, 1-ack, 2-probe req, 3-random data, 4-user data

Our approval consultant asks what "random data" actually is - PN9, PN15, something else?

Hope somebody knows - thanks in advance!