Loading 7831R memory with contents of Array from Host VI?

Question

Hi,
Can anyone help - how can I load the contents of an array in the
labview Host VI into the memory of the FPGA on the 7831 board? When I
try to do this in a FOR loop, and index each element, it says that the
array must be a fixed size for this target. How do I do this? I
initialise the array in an earlier sequence frame, and am reading from
a local variable.
Thanks for any advice,
Joe.

Answer 1

In LabVIEW FPGA all arrays must have a fixed size, because they are allocated as static memory on the FPGA. As much as possible you should avoid allocating (large) arrays in your LabVIEW FPGA diagram since this will use a lot of FPGA space; about 1% of the FPGA for every 4 bytes of array data.
Instead of using an array in your diagram you can use the Memory Read and Write functions which provide access to 16kB of memory which is separate from the FPGA.
If you want to use an array as you described, you should create an array constant in your diagram or an array control on your front panel. To set the size, right click on the array index display and select 'Set Dimension Size'. Select the fixed size and specify the number of elements in the array.
T
o pass values to an array on the diagram use the 'Array Replace Subset' function on the existing array.
If you have an array control on your front panel you can directly pass the whole array from your host application to the FPGA VI and do not need to pass individual array elements.
Christian L
NI Consulting Services
Christian Loew, CLA
Principal Systems Engineer, National Instruments
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