JTAG Switch

A hardware and software solution for automatically switching JTAG debuggers between multiple test benches in automated hardware testing environments.

Overview

The JTAG Switch enables efficient sharing of expensive or limited-availability JTAG debuggers across multiple hardware test benches. Instead of purchasing dedicated debuggers for each test bench in CI/CD pipelines, a single JTAG debugger can be dynamically routed between two independent test targets, maximizing hardware utilization while maintaining testing throughput.

Project Structure

This repository contains both hardware and software components:

Hardware (hw/)

Arduino shield PCB design for JTAG multiplexing hardware:

• KiCad Project: Complete schematic and PCB layout
• Files: jtag_switch.kicad_sch, jtag_switch.kicad_pcb
• Interface: Arduino-compatible headers for connection to microcontroller EVBs
• Switching: Two independent GPIO-controlled select lines for JTAG routing

The shield plugs into any Arduino-compatible microcontroller evaluation board and provides the physical JTAG switching circuitry.

Software (sw/)

Zephyr RTOS firmware for controlling the JTAG switch hardware:

• Platform: Runs on any Zephyr-supported microcontroller with Arduino headers
• Supported Boards:
  • FRDM-K64F (NXP Kinetis K64) - primary development board with Ethernet
  • FRDM-MCXC444 (NXP MCX C444) - development board with USB serial only
• Control Interfaces:
  • USB serial shell (115200 baud)
  • Ethernet REST API with JSON endpoints
  • Web-based UI with real-time control
• Safety: Enforces mutual exclusion - both GPIO select lines never HIGH simultaneously

See sw/jtag-switch/README.md for complete software documentation including build instructions, API reference, and testing information.

Quick Start

Hardware Setup

1. Open the KiCad project in hw/ to view or manufacture the Arduino shield
2. Assemble the shield and mount it on a compatible microcontroller EVB
3. Connect JTAG debugger and target devices to the shield connectors

Software Setup

# Navigate to software directory
cd sw

# Set up Zephyr environment
source .venv/bin/activate
source zephyr/zephyr-env.sh

# Build and flash firmware (FRDM-K64F)
west build -b frdm_k64f jtag-switch
west flash

# Or build and flash firmwarefor FRDM MCXC444
west build -b frdm_mcxc444 jtag-switch
west flash


### Usage

**Via USB Serial:**
```bash
screen /dev/ttyACM0 115200
uart:~$ jtag status
uart:~$ jtag select0 1

Via REST API:

# Get current status
curl http://192.168.1.100/api/status

# Switch to connector 1 on select line 0
curl -X POST "http://192.168.1.100/api/select?line=0&connector=1"

Via Web UI:

Navigate to http://192.168.1.100/ in a web browser for graphical control.

Documentation

• Software Details: sw/jtag-switch/README.md
• Software Development Guide: sw/jtag-switch/CLAUDE.md
• Hardware Design: Open hw/jtag_switch.kicad_pro in KiCad

License

SPDX-License-Identifier: Apache-2.0