Probe disabled (in a vi that accesses FPGA nodes), why?

Question

Hi all,
I have problems with debugging code I wrote for a project that runs on a cRIO device. In one of the sub-vi's  on the RT target I am trying to write to analog outputs on this
device by calling a read/write node to access the FPGA devices. This vi "crashes" for some reason. Strangely enough, I cannot debug this vi (debugging is enabled),
but the probe menu item is disabled. The probe tool is still active but does not do anything. So I am unable to track the problem here. Why? The only thing I know is
that the vi returns with an error -1073807346 and afterwards the FPGA reference is "empty" so I have lost the connection to the FPGA and further parts
of the program cannot access the hardware anymore.
Maybe I should mention that the code I am using to access the FPGA is derived from some examples provided by NI, but I guess this does not affect the probe item?
Any ideas what the problem might be?
Thanks,
Olaf

Answer 1

Hi again,
I finally could find the problem. Actually, the FPGA reference was lost somwhere else already in another sub-vi which is not finished yet. For some reason
other parts of the software - those who got a valid FPGA reference upon first call - still worked even when they were called with a meanwhile empty reference
which is stored in a shift register in the main loop. This is a behaviour of Labview I will never fully understand, that it "stores" and remembers data in some
registers even though it should have been overwritten. This makes debugging hard because you suspect the error somewhere else.
The still remaining question is why I cannot use variable probes in those sub-vi's on the RT target that use FPGA interface nodes to read or write data to the FPGA-vi.
Olaf
Olaf Stetzer wrote:
Hi all,
I have problems with debugging code I wrote for a project that runs on a cRIO device. In one of the sub-vi's  on the RT target I am trying to write to analog outputs on this
device by calling a read/write node to access the FPGA devices. This vi "crashes" for some reason. Strangely enough, I cannot debug this vi (debugging is enabled),
but the probe menu item is disabled. The probe tool is still active but does not do anything. So I am unable to track the problem here. Why? The only thing I know is
that the vi returns with an error -1073807346 and afterwards the FPGA reference is "empty" so I have lost the connection to the FPGA and further parts
of the program cannot access the hardware anymore.
Maybe I should mention that the code I am using to access the FPGA is derived from some examples provided by NI, but I guess this does not affect the probe item?
Any ideas what the problem might be?
Thanks,
Olaf