Detecting whether ATN is asserted or un-asserted

I have been working on a low level approach to driving a GPIB device and 
found the ibcac() and ibgts() functions, however, I cannot find a way to 
test whether the signal is asserted or un-asserted. For example, there 
is ibsta, but this is a on-shot value returned when calling a function 
but doesn't then tell me what has happened to the state of ATN after 
calling the function. For example, after un-asserting ATN, I need to 
make sure that the signal is high before sending data.

I also discovered iblines(), but this returns a constant value of 32768.

There is also ibcmd() which writes "command bytes", but I am unsure 
whether this actually asserts ATN or not while doing so or whether 
asserting ATN has to be done separately? How does this differ to ibwrt()?

My interface is a National Instruments PCI card dated 1997 and marked 
PCI-GPIB+. It uses the tnt4882 driver. I am working on Linux,

I would appreciate a little guidance on how to manage ATN manually.

Thank you.