====== Using TCL for Fame and Fortune ======

If you hate to type repetitive TCL commands to exercise your design, here are some ideas.

It turns out TCL is a full-featured programming language (even if it is verbose and perhaps clunky).
But, once you find some examples to cannibalize, it can be pretty easy to create very compact simulation scripts.

====Using Looping to Exercise All Combinations of 1's and 0's====
The following code sample shows how to loop across all combinations of 4-bits (from 0000 to 1111).

Note that when you set a variable name you just state it but when you want to get at the value stored in that variable you must prefix it with a $ sign.

Note also that you call functions using [functionName ... ] syntax.  In this case, "expr" evaluates an arithmetic expression.

  set i 0
  while {$i < 16} {
    set a [expr ($i >> 3) & 1]
    set b [expr ($i >> 2) & 1]
    set c [expr ($i >> 1) & 1]
    set d [expr ($i >> 0) & 1]
    puts "Test this combination: $a $b $c $d"
    add_force mySignal3 $a
    add_force mySignal2 $b
    add_force mySignal1 $c
    add_force mySignal0 $d
    run 100ns
    incr i
  }
  
Or, it could be much simpler:

  set i 0
  while {$i < 16} {
    add_force mySignal3 [expr ($i >> 3) & 1]
    add_force mySignal2 [expr ($i >> 2) & 1]
    add_force mySignal1 [expr ($i >> 1) & 1]
    add_force mySignal0 [expr ($i >> 0) & 1]
    run 100ns
    incr i
  }

Or, if what you are forcing is itself a 4-bit quantity, it requires a function to be defined first to do the integer to binary conversion:

  proc dec2bin i {
    #returns a string, e.g. dec2bin 12 => 1100 
    set res {} 
    while {$i>0} {
        set res [expr {$i%2}]$res
        set i [expr {$i/2}]
    }
    if {$res == {}} {set res 0}
    return $res
  }
  
  set i 0
  while {$i < 16} {
    add_force a [dec2bin $i]
    run 10ns
    incr i
  }
 
And, if you prefer for-loops:

  for {set i 0} {$i < 16} {incr i} {
    add_force mySignal [dec2bin $i]
    run 100ns
    incr i
  }