There are many statements where we need to execute commands till the condition is met, these are called Loops in TCL. Mainly we use FOR, FOREACH and WHILE Loops in VLSI.
Types of Loops#
FOR Loop
Format:
for {initialization} {condition} {Increment} { statements }Flow Diagram
Example:
for {set a 5} {$a < 10} {incr $a} { puts “The value of a is : $a” }Result:
The value of a is : 5 The value of a is : 6 The value of a is : 7 The value of a is : 8 The value of a is : 9WHILE Loop
Format
while {condition} { Statement }Flow Diagram
Example:
set a 5; while {$a < 10} { puts “The value of a is : $a” }Result:
The value of a is : 5 The value of a is : 6 The value of a is : 7 The value of a is : 8 The value of a is : 9Infinite Loop
Sometimes few loops can be infinite, these loops are intended sometimes but if not then the runtime of any execution will shoot up. Below is the infinite loop.
while {1} { puts “This is infinite loop” }FOREACH Loop
Whenever we have a collection of objects and we need to have iterations for all the objects then we can use foreach loop.
Syntax:
foreach <object_name> <collection_of_objects> { Body }Example:
set a {1 2 3 4 5} foreach b $a { puts “The value is $b” }Result:
The value is 1 The value is 2 The value is 3 The value is 4 The value is 5NESTED Loop
Nested loops are the loops inside a loop. Nested loops can be an if loop inside an if loop or while loop inside a while loop or if loop inside while or while loop inside if loop, so basically it can be any of these. One syntax is as per below.
Syntax:
while {condition} { for {initialization} {condition} {increment} { statements } statements }Loop Control Statements#
Sometimes we need to control a loop hence we need to control statement and change its normal sequence.
Break
Let’s understand this with an example.
set a 10; while {$a < 20} { puts “The value of a : $a” incr a; if {$a>15} { break } }Result:
The value of a : 10 The value is a : 11 The value is a : 12 The value is a : 13 The value is a : 14 The value is a : 15
Continue
Set a 10; While {$a < 20} { If {$a == 15} { Incr a Continue } Puts “The value of a : $a” Incr a }Result:
The value of a : 10 The value of a : 11 The value of a : 12 The value of a : 13 The value of a : 14 The value of a : 15 The value of a : 16 The value of a : 17 The value of a : 18 The value of a : 19
Written by
Swasti Pujari
Associate Director, Backend Engineering at CoreIC Technologies, with 15+ years in VLSI Physical Design and backend engineering. Previously Practice Head at UST Global, leading Physical Design, STA, EMIR, DFT, and Physical Verification. Delivered 3nm, 6nm and 7nm projects for AMD, Intel, and Microchip, and published IEEE research on hybrid AI-EDA floorplanning.
