As for the memory of user application space, when the using area of
system memory is full, it is shunted onto the hard disk.
In this help, the case that the memory not been shunted is called "Memory
Locked", and the opposite case is called "Memory Unlocked".
The memory is automatically locked when the buffer setting function is
executed.
The memory is automatically unlocked when the data transfer to the sampling
buffer is complete.