• double*
  return current value
• double
  actual time
• char*
  node name
• int
  identification number of calling ngspice shared lib
• void*
  return pointer received from caller

Ask for ISRC EXTERNAL value. The independent current source (see Chapt. 4.1) with EXTERNAL option allows to set a current value to the node defined by the netlist and named here at the time returned by the simulator.