void rtic_get_data(struct data_struct *data):
this function returns the next data point that appears in xrtic. It loads the data into the structure ``data'', for
which the user should have already allocated memory. If there is no
data to be read, this function blocks until a new data point
arrives. The data structure takes on the following form (defined
in main.h):
struct data_struct
{
long long time; /* nano-seconds of
actual run-time */
int factor; /* downsample ratio */
float val[RTIC_MAX_DATA_BUF]; /* user specified return
values */
};