Accessing Multiple Address Spaces

You can use LLA operations to access only the address space currently mapped. To access a different address space, you need to perform a remapping, which involves calling viUnmapAddress() and viMapAddress(). Therefore, LLA programming becomes more complex, without much of a performance increase, for accessing several address spaces concurrently. In these cases, the HLA operations are superior.

In addition, if you have several sessions to the same or different devices all performing register I/O, they must compete for the finite number of windows available. When using LLA operations, you must allocate the windows and always ensure that the program does not ask for more windows than are available. The HLA operations avoid this problem by restoring the window to the previous setting when they are done. Even if all windows are currently in use by LLA operations, you can still use HLA functions because they will save the state of the window, remap, access, and then restore the window. As a result, you can have an unlimited number of HLA windows.