Value Change Dump (.vcd) command line viewer for Windows, Linux and MacOS

# SKIP=13 vcd < samples/basic.vcd
global:
  zoom: 2
  date: Fri Nov 21 16:56:29 2014
  total: 43
  skip: 13
  time:
    scale: 1.00
    unit:  fs
    line       : "13                  23                  33                  "
channels:
  default:
    e_clk      : "╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔"
    e_rst      : "▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔"
    e_ren      : "▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁╱▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔"
    e_wen      : "▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔╲▁▁▁╱▔▔▔╲▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔"
    e_d[3:0]   : "3 3 4 4 5 5 Z Z 6 6 Z Z 7 7 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z "
    e_q[3:0]   : "Z Z Z Z Z Z Z Z Z Z Z Z Z 3 3 Z Z 4 4 5 5 6 6 7 7 0 0 Z Z Z "
    e_empty    : "▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔"
    e_mid      : "▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁"
    e_full     : "▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁"
  fifo1:
    clk        : "╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔╲▁╱▔"
    rst        : "▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔"
    ren        : "▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁╱▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔"
    wen        : "▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔╲▁▁▁╱▔▔▔╲▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔"
    d[3:0]     : "3 3 4 4 5 5 Z Z 6 6 Z Z 7 7 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z "
    q[3:0]     : "Z Z Z Z Z Z Z Z Z Z Z Z Z 3 3 Z Z 4 4 5 5 6 6 7 7 0 0 Z Z Z "
    empty      : "▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔"
    mid        : "▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁"
    full       : "▁▁▁▁▁▁▁▁▁▁╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁"
    w_adr[1:0] : "2 3 3 0 0 1 1 1 1 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 "
    r_adr[1:0] : "1 1 1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 0 0 1 1 2 2 3 3 3 3 3 3 3 "

Installation

From prebuilt binary

Manually download install a prebuilt binary

From sources

make
sudo make install

From Package Manager

Arch-based distribution:

yay -S vcd

Usage

vcd < in.vcd            # output to screen
vcd < in.vcd > out.yml  # output to file
vcd < in.vcd | less -S  # scrollable view

Query

The default vcd output is a valid YAML file, so you can process it with many tools like yq or shyaml

# print the first 9 sample of the clk channel in the fifo1 scope
vcd < samples/basic.vcd | yq .channels.fifo1.clk[0:9]
vcd < samples/basic.vcd | shyaml -y get-value channels.default.e_clk

Styling

Waveform, position, color can be customized using environment variables.

# skip the 9 first samples
SKIP=9 vcd < in.vcd | less -S
# Disable RAISE/DROWN transition
RAISE="" DROWN="" vcd < in.vcd
# color the bus value in green using StartTeX/EndTeXt (STX/ETX) variables
STX=$(printf "\x1b[32m") ETX=$(printf "\x1b[0m") vcd < in.vcd

Auto-Refresh

The following snippet endlessly wait for a change on the in.vcd file. Then, when it happen, regenerate the out.yml graph and refresh the less -S out.yml scrollable display by sending a "R" keypress (for refreshing).

echo "hi ! please modify 'in.vcd' to refresh me" > out.yml
while inotifywait -q -e modify -e close_write in.vcd ; do
  vcd < in.vcd > out.yml           # regenerate out.yml
  screen -x -r bridge -X stuff R   # send Refresh command to foreground less -S
done &                             # this loop will run in background
screen -S bridge less -S out.yml   # the foreground "less -S" display
# don't forget to stop the background loop using `kill %1` or fg + ^C