1) How is CSpin to be specified, as IO-pin or PCA5 pin?
You have to do nothing at all. Pin 29 should be CS by default.
2) Why don't we see CS going low during read and write actions?
I am back in the office at 22.4.14 i will check it than. But it is stange, because we have only to register the CS all other things should be done by the processor. Maybe there is a bug in the driver ... .
3) Does NativeSPI use some other pin for CS?
At the time only one pin is usabel. But we can expand the driver so that more than one pin is useable as CS.