get_drivers

Get the drivers of a net or pin (LLM: drivers)
Usage: @drivers = get_drivers($point, @options);
$point: net name or pin name, 'n12345' or 'U12345/A1'
@options:
   -nonbuf: Trace the drivers until none buffer 
@drivers: An array of the drivers, if the point is floating, @drivers is empty, 
         if the point has multi-drivers, @drivers has more than one items.
         For each item in @drivers
         Index 0: instance, it is empty if the driver is port
         Index 1: pin or port, if the driver is port, return port
         Index 2: string "pin" or "port" depending on the driver is port or leaf cell
         Index 3: indicating drive path inverted or not
         If 'nonbuf' is present, the last item in @drivers is the non-buffer driver
         So '$nonbuf = pop @drivers' can get the non-buffer driver 
Note:
Use 'get_driver' instead if the net has only one driver and 'nonbuf' option is not used

Examples:

#1. Get drivers of a net
@drivers = get_drivers("net12345");
@drivers has content of (["U1247", "Y", "pin"]);

#2. 'port_abc' is input port
@drivers = get_drivers("port_abc"); 
@drivers has content of (["", "port_abc", "port"]);
   
#3. Buffers in the path
 @drivers = get_drivers("state_reg/CK", "-nonbuf");
 @drivers has content of
  (
    ["buf_inst0", "Y", "pin"],
    ["inv_inst1", "Y", "pin"],
    ["and_inst2", "Y", "pin"]
  )