Arrays in Optimized FPGA VIs must be of a fixed size to ensure proper memory allocation on the FPGA at compile time.
The type of input you wire to an array determines whether you need to take additional steps to designate a fixed size for the array:
When you wire an indicator to an array, LabVIEW automatically sets a fixed size for the output that scales to the size of the array. This behavior is the default setting and you can view this setting on an array indicator in the Auto Adapt section of the Item tab.
In some situations, LabVIEW may not be able to determine the size of the array, in which case you can manually set the indicator to be a fixed size. Use the manual setting on an indicator only when LabVIEW cannot determine the size of the array because the setting can cause coercion dots to appear later in development.
When you manually set an indicator to fixed size, the Auto Adapt option is set to Don't Auto Adapt. If you then switch the indicator back to a variable size, the option does not automatically switch back to Auto Adapt, meaning LabVIEW no longer automatically sets the size of the indicator to the size of the array, as per the default behavior. Therefore, when you switch an indicator from fixed size back to variable size, you have to manually enable Auto Adapt to allow LabVIEW to automatically determine the size of the array output.