Q: I receive an error about invalid PD from iol-master-appl

[12:53:29 WARN ] generic_run0: PDIn data is invalid for port 1
or 
[12:48:33 WARN ] generic_run0: Failed to get PDIn from port 1, len requested=4, len act=2

A: To exchange process data (PD), both PDIn and PDOut have to match the device

Process data is exchanged automatically in the background as soon as the connected device is powered. If the PD has never been set by a PD command, the PD is marked as invalid (PDIn and PDOut length = 0).

The length of the PD is reported back from the device on connection. If there is a mismatch between the set and reported length, the PD fails to match.

Per SDCI specification, the PD is always fully exchanged (send full PDOut, receive full PDIn).