The below does two things:
(i) do not try to spin up a CF reader without media
(ii) be careful when asking for the cache parameters mode page

[do not ask for this page when no media are present:
it is meaningless, and some devices react badly if we do;
check the reply so that we do not read past the end of the reply;
first give a small transport length - some USB devices are unhappy
if we ask for more than they provide]

Andries