• int
  node index
• double
  actual simulation time
• double
  a real value for specified structure component for plotting purposes
• char*
  a string value for specified structure component for printing
• void*
  a binary data structure
• int
  size of the binary data structure
• int
  the mode (op, dc, tran) we are in
• int
  identification number of calling ngspice shared lib
• void*
  return pointer received from caller

Upon a time step finished, called per node.