Sets a breakpoint in ngspice, a time point that the simulator is enforced to hit during the transient simulation. After the breakpoint time has been hit, the next delta time starts with a small value and is ramped up again. A breakpoint should be set only when the background thread in ngspice is not running (before the simulation has started, or after the simulation has been paused by bg_halt). The time sent to ngspice should be larger than the current time (which is either 0 before start or given by the callback GetSyncData (19.6.3.3). Several breakpoints may be set.