Module 69 min

Parsing Reports

Strings, regexp, and reading files

A huge part of real EDA scripting is pulling numbers out of tool reports: how many violations, what is the worst slack, total power. This means string handling and file reading.

String basics

tcl

set line "WNS = -0.123 ns"
puts [string length $line]            ;# length
puts [string match "*WNS*" $line]     ;# 1 if it contains WNS
puts [string trim "  spm  "]          ;# -> spm (trims spaces)

Pulling out a number with regexp

Regular expressions extract exactly the piece you want. Here we grab the slack value from a report line.

tcl

set line "WNS = -0.123 ns"
if {[regexp {WNS = (\S+)} $line -> wns]} {
  puts "Worst negative slack is $wns"   ;# -0.123
}

Reading a report file line by line

tcl

set viol 0
set fh [open "timing.rpt" r]
while {[gets $fh line] >= 0} {       ;# gets returns -1 at end
  if {[string match "*VIOLATED*" $line]} {
    incr viol
  }
}
close $fh
puts "Found $viol violated paths"

Writing a file

tcl

set out [open "summary.txt" w]
puts $out "Violations: $viol"
close $out

Pro tip

regexp with a capture group in parentheses, written to a variable after the ->, is the everyday tool for scraping numbers from reports. Combined with reading a file line by line, you can turn any tool report into a one-line summary or a pass/fail check.

Watch out

always close a file you open, especially in a loop, or you will run out of file handles on a long run. Open, use, close - every time.