basic.%setflush

sets the flush periods.
The normal flush period is set to the number of seconds specified by 'newp', the forced flush period to 'newfp' and the previous values are returned into 'oldp'. The upper 16 bits of the (int) 'oldp' is the value of the forced flush period, and the lower 16 bits, the value of the normal flush.

If 'newp' is null, no change is made to the normal flush.
If 'newfp' is equal to -2, no change is made to the forced flush.
If 'newfp' is equal to -1, the forced flush is disabled.
If 'newfp' is equal to 0, the forced flush is set into 'immediate write' mode.