Lists, the TCL Workhorse
Building and walking lists of objects
Lists are everywhere in TCL and in EDA scripting, because a design is full of lists: lists of cells, ports, clocks, files. Knowing list commands well is most of practical TCL.
Creating and indexing
set corners {ss ff tt} ;# a 3-element list
puts [lindex $corners 0] ;# first element -> ss
puts [llength $corners] ;# how many -> 3
lappend corners sf ;# add an element -> ss ff tt sfLooping over a list
foreach is the command you will use most. It runs a body once per element.
foreach corner $corners {
puts "Reading library for corner: $corner"
}
# foreach can walk several lists at once
foreach port {clk rst d} dir {input input input} {
puts "$port is an $dir"
}Associative arrays
When you want to look something up by a key rather than a position, use an array. An array maps keys to values, like a dictionary.
set period(clk) 1.25
set period(refclk) 20.0
puts $period(clk) ;# 1.25
foreach name [array names period] {
puts "$name -> $period($name)"
}in real flows you keep settings in arrays or lists at the top of the script (corner names, clock periods, file lists) and loop over them, so adding a corner or a file is a one-line change. Data at the top, logic below, is the mark of a clean EDA script.
a TCL list is space-separated, so an element containing spaces must be braced or quoted, or it will be split into several elements. When in doubt build lists with the list command, which quotes correctly for you.
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