Linux, Unix, GVIM, for VLSI Workflows

This guide provides a structured roadmap for developing skills in the Linux environment, powerful text-processing tools, and professional VLSI industry workflows and design fundamentals.

1. Linux/Unix Fundamentals & Essential Commands

Navigate the filesystem with confidence using these foundational tools.

Advanced Command Line History

• !!: Re-run the last command.
• !$: Access the last argument of the previous command (e.g., mkdir dir; cd !$).
• Ctrl+r: Search backwards through command history.
• history | grep "vcs": Search specifically for old simulation command strings.

Symbolic Links & Aliases

• ln -s /path/to/original link_name: Create a shortcut (Essential for linking shared project libraries).
• alias l='ls -ltr': Create a shortcut command. Add to .bashrc for persistence.
• alias ..='cd ..': Navigate faster with simple aliases.

2. GVIM for Efficient Text Handling

GVIM is the industry standard for editing HDL code (Verilog/VHDL) and large log files.

Mode Awareness

• Normal Mode (Esc): Your “home base” for navigation and deletion.
• Insert Mode (i): Standard text entry.
• Visual Block (Ctrl+v): Critical for column-based editing in Verilog port lists.

Stability Shortcuts

• :w / :x: Save / Save and Close.
• u / Ctrl+r: Undo and Redo.
• :%s/old/new/gc: Global find/replace with confirmation (safer for large files).
• :set hls incsearch: Enable highlighting and incremental search for faster debugging.

Multitasking with Splits

• :sp filename: Split window horizontally to view two files.
• :vsp filename: Split window vertically (Best for comparing two pieces of code).
• Ctrl+w [Arrow]: Move the cursor between different split windows.

The .vimrc Customization

Create a .vimrc file in your home directory to make these settings permanent:

syntax on            " Enable syntax highlighting for Verilog/VHDL
set tabstop=4        " Number of spaces that a <Tab> in the file counts for
set shiftwidth=4     " Number of spaces to use for each step of (auto)indent
set expandtab        " Use spaces instead of tabs (industry best practice)
set cursorline       " Highlight the current line for better visibility
set number           " Show line numbers
set ignorecase       " Search is case-insensitive
set smartcase        " ...unless search contains uppercase letters

3. Powerful Symbols Processing & Regular Expressions

Understanding metacharacters is the key to mastering grep, sed, and awk.

Regex Metacharacters Reference

Symbol	Meaning	Example & Result
^	Start of a line	grep "^module" – Finds lines starting with ‘module’
$	End of a line	grep ";$" – Finds lines ending with a semicolon
.	Any single character	grep "r.n" – Matches ‘run’, ‘ran’, ‘r2n’
*	Zero or more of previous char	grep "ab*" – Matches ‘a’, ‘ab’, ‘abbb’
[]	Any character in brackets	grep "[0-9]" – Matches any digit
[^]	Any character NOT in brackets	grep "[^0-9]" – Matches non-digits
\	Escape metacharacter	grep "\." – Matches a literal period ‘.’

Robust One-Liners

• grep -E "Error|Fatal" run.log: Search for multiple critical patterns using extended regex.
• sed -i.bak 's/VDD/VCC/g' design.v: In-place edit with automatic backup.
• awk '$3 > 0.0 {print "Violation at: " $1}' timing.rpt: Extract violations where slack is positive.

Advanced File Selection

• find . -name "*.v" | xargs grep "module": Efficiently search through thousands of Verilog files.
• grep -r "module_name" . --include="*.v": Search only Verilog files in all subdirectories.

4. System Administration & Process Control

Prevent system crashes by monitoring resource consumption.

• top -u $USER: Monitor only your own simulation processes.
• nice -n 19 ./simv: Run simulations with low priority to keep the server responsive.
• df -h .: Check disk space for the current partition only.

Networking & Remote Access

• ssh -Y user@server: Connect with Trusted X11 forwarding (required for tools like Verdi/DVE).
• scp local_file user@server:/path/: Securely copy files between your workstation and the simulation server.
• rsync -avz project/ user@server:backup/: Synchronize large project folders efficiently (only copies changes).

5. Shell Scripting for Stability

Use defensive programming in Bash to ensure scripts don’t fail silently.

#!/bin/bash
# Defensive Scripting Pattern
set -euo pipefail # Fail on error, unset vars, or pipe failure

DESIGN_NAME="${1:-cpu_core}" # Default value if argument is missing
LOG_FILE="sim_${DESIGN_NAME}.log"

echo "[$(date)] Starting Simulation: $DESIGN_NAME"

# Check if required tool exists before running
if ! command -v vcs &> /dev/null; then
    echo "Error: VCS tool not found in PATH."
    exit 1
fi

# Run simulation and check exit code
vcs -f filelist.f -o simv && ./simv > "$LOG_FILE" 2>&1 || {
    echo "Simulation crashed. Check $LOG_FILE"
    exit 1
}

if grep -qi "error" "$LOG_FILE"; then
    echo "FAILED: Errors found in log."
else
    echo "SUCCESS: Simulation completed."
fi

6. VLSI Workflows & Server Management

Manage high-performance computing (HPC) resources effectively.

• LSF Submission: bsub -R "rusage[mem=8192]" ./simv (Always request specific memory to avoid being killed).
• Environment Control: module purge; module load tool/version (Ensures a clean environment before runs).
• X11 Persistence: Use tmux or screen to keep sessions alive even if the network drops.

LSF Monitoring Examples

• bjobs -u all: See the global queue to check server congestion.
• bkill 0: Kill all jobs submitted by you (useful if you realize a script has a bug).
• bpeek [job_id]: Peek at the output of a running job without waiting for it to finish.

7. Security, Backup & Maintenance

• Version Control: While cp is fine, use git for true stability and history tracking.
• Automated Cleanup: find . -name "*.log" -mtime +7 -delete (Delete logs older than 7 days to prevent disk-full errors).
• Secure Permissions: chmod -R 700 ~/private_project (Protect your intellectual property from other users on the shared server).

Common Debugging Workflow

1. Check disk space: df -h .
2. Check memory/CPU: top -c
3. Identify hanging processes: ps -ef | grep $USER
4. Force terminate if necessary: kill -9 [PID]