commodore 65 kernal functions

I'm trying to port something from c64 mode to c65 mode, but it never
returns from OPEN ($ffc0) when trying to read from $0:*

I currently am using xemu, but I can't find any c65 samples that do
anything with files on disk & so I can't rule out there is a bug in xemu.

I have

0 BANK0:SYS8209

I've added a SETBANK call at the start and tried all manner of MAP &
even putting some code <$2000 that switches to system map, calls the
kernal and then switches the map back.

It seems like something fundamental and yet isn't documented anywhere.

Some c65 samples don't touch disk, some need a later version of the rom
from mega65 (which I don't have access to).


I kinda figure that reading the list of files on disk from machine code
is something that someone would have needed to do.

Any help would be appreciated


Thanks