Vi, Vim, GVim and Nano for RTL/DV

Explanation

Choose the editor that fits the session

Linux engineering systems may provide several editors. Use the one installed and approved on the workstation.

Check availability before choosing:

command -v vi
command -v vim
command -v gvim
command -v nano

A missing command is not an error in your work. Choose another installed editor or ask which editor the lab supports.

Vim and Vi modes

Vim starts in Normal mode. Keys in Normal mode are commands rather than inserted text.

Use :q! only when you deliberately want to discard every unsaved change.

Move through a file in Vim

Return to Normal mode with Esc before using these keys.

Edit and indent efficiently in Vim

Vim combines an action with a movement. For example, dw deletes from the cursor to the next word and 5dd deletes five lines.

Use Visual block mode carefully when editing aligned declarations. A rectangular edit can change several signal declarations at once, but it can also damage columns that were not meant to change.

Nano shortcuts

Nano shows shortcuts using ^ for Ctrl and M- for Alt. For example, ^O means Ctrl+O.

Start Nano with visible line numbers when reviewing diagnostics that contain a line number:

nano --linenumbers rtl/counter.v

For multiple files, start nano --multibuffer file1 file2. Use Alt+< and Alt+> to move between buffers. Availability of long options can vary; check nano --help on the workstation.

Work with multiple RTL files in Vim

Open related files together:

vim rtl/counter.v tb/tb_counter.v

Save each changed buffer deliberately. Vim warns when a command would abandon unsaved work; read the message instead of adding ! automatically.

Search an RTL project from Vim

From the project root, search Verilog files and open a quickfix list:

:vimgrep /module/j rtl/**/*.v
:copen
:cnext
:cprevious

For SystemVerilog, use rtl/**/*.sv. :vimgrep stores matches in the quickfix list, allowing you to visit each file and line. Close the list with :cclose.

GVim on a workstation

Start GVim with a file path:

gvim rtl/counter.v

GVim needs a graphical desktop or forwarded display. On a headless compute server, use terminal Vim instead. Do not enable graphical forwarding only to edit a small file if the approved environment does not support it.

Use a small, team-compatible Vim configuration

Test settings inside Vim before saving them in ~/.vimrc:

:set number
:set expandtab
:set tabstop=4
:set shiftwidth=4
:set softtabstop=4
:set autoindent
:syntax on

When the settings match the project style, a minimal ~/.vimrc can contain:

set number
set expandtab
set tabstop=4
set shiftwidth=4
set softtabstop=4
set autoindent
syntax on
filetype plugin indent on

Follow the repository formatting rules when they differ. An editor configuration should help produce the required style, not silently rewrite an entire existing codebase.

Worked example

Create and edit a Verilog file with Vim

mkdir -p "$HOME/asic-linux-practice/editor-lab/rtl"
cd "$HOME/asic-linux-practice/editor-lab"
vim rtl/counter.v

Inside Vim:

1. Press i to enter Insert mode.
2. Type the module below.
3. Press Esc to return to Normal mode.
4. Enter :set number to show line numbers.
5. Enter /count to search for count; use n for the next match.
6. Enter :wq to save and exit.

module counter (
    input  wire       clk,
    input  wire       reset_n,
    output reg  [3:0] count
);
    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            count <= 4'd0;
        end else begin
            count <= count + 4'd1;
        end
    end
endmodule

Verify the saved file without changing it:

sed -n '1,20p' rtl/counter.v
grep -En 'module|always|endmodule' rtl/counter.v

Expected result: the file contains one module, one sequential always block, and one endmodule. The line numbers from grep -En show where each item appears. This example uses Verilog-2001 syntax, so it does not require SystemVerilog mode.

If Icarus Verilog is available, perform a syntax-only compile:

iverilog -g2005 -tnull rtl/counter.v
printf 'compile-status=%s\n' "$?"

A valid module returns status 0 and normally prints no output.

Review two files side by side

After creating tb/tb_counter.v, open both files:

vim -O rtl/counter.v tb/tb_counter.v

Vim opens vertical splits. Use Ctrl+w followed by h or l to change windows. Search for counter in each file, run :set list to reveal tabs and trailing spaces, then use :set nolist to return to the normal display.

Repeat a small edit with Nano

nano rtl/counter.v

Use Ctrl+W to find counter, add a short comment, save with Ctrl+O, and exit with Ctrl+X. Run diff against a backup if you need to review exactly what changed.

Protect engineering work

Before a broad edit, create a deliberate backup or use version control:

cp -i rtl/counter.v rtl/counter.v.before-edit
vim rtl/counter.v
diff -u rtl/counter.v.before-edit rtl/counter.v

Vim may create a swap file when a session is interrupted. Read the recovery message carefully. Use vim -r path/to/file when recovery is appropriate; do not delete a swap file until you confirm that another editing session is not active.

Common mistakes

• Typing text in Vim Normal mode and accidentally running commands.
• Forgetting Esc before entering :wq or another command.
• Using :q! and unintentionally discarding useful changes.
• Running two editors on the same file and overwriting newer work.
• Editing generated simulation output instead of the RTL or testbench source.
• Opening GVim on a server without a graphical display.
• Adding editor backup and swap files to source control.
• Forcing a command with ! without reading why Vim refused it.
• Re-indenting an entire existing file without reviewing the diff.
• Mixing tabs and spaces against the repository formatting rules.

Check yourself

Which Vim key returns to Normal mode? How do w, gg, and % move the cursor? What is the difference between :q and :q!? Which command opens a vertical split? In Nano, which shortcut saves the current file?