TCL Inside EDA Tools

Plain TCL is the foundation. Inside a tool like Design Compiler or PrimeTime, the real power is the tool commands that hand you pieces of the design to work on. Those pieces come as collections.

Collections, not lists

When you ask a tool for objects, it returns a collection: a tool-managed group of design objects (cells, pins, ports, clocks). It looks like a list but is handled with its own commands, because a real design can have millions of objects and the tool keeps them efficiently.

# get_* commands return collections of design objects
set ffs   [get_cells -hier -filter "is_sequential==true"]
set dpins [get_pins core/data_reg*/D]
set clks  [get_clocks]

puts "Flip-flop count: [sizeof_collection $ffs]"

Walking a collection

Use foreach_in_collection, not plain foreach, to loop over the objects a tool returns.

foreach_in_collection clk [get_clocks] {
  set name   [get_attribute $clk name]
  set period [get_attribute $clk period]
  puts "Clock $name has period $period"
}

A small but real example

Put it together: report every clock and flag any with a tight period.

foreach_in_collection clk [get_clocks] {
  set name   [get_attribute $clk name]
  set period [get_attribute $clk period]
  if {$period < 2.0} {
    puts "FAST clock $name : $period ns"
  }
}