Evaluating Custom RISC-V Industrial Controllers

I was recently engaged to explore whether a custom RISC-V platform could replace aging proprietary controllers in a specialty packaging line. Below is the evaluation framework we used and the key lessons learned while prototyping the stack.

1. Business Motivation

• Cost Pressure: OEM replacement boards cost more than $3,000 and had 16-week lead times.
• Flexibility: The customer needed to adapt machine recipes frequently and wanted a platform amenable to modern toolchains (Git, CI/CD, containerized deployments).
• Openness: Avoid vendor lock-in and licensing surprises when scaling internationally.

2. Hardware Selection Criteria

We benchmarked three RISC-V SoMs that offered industrial temperature ratings:

We chose Vendor B for pilot runs because the integrated isolated IO reduced our PCB work, even though memory was constrained.

3. Software Stack Overview

• RTOS: Zephyr with the Time-Sensitive Networking (TSN) add-on for deterministic Ethernet.
• Middleware: FreeModbus, custom EtherCAT master, and a lightweight MQTT client.
• Application Layer: Structured text translated to C using PLCopen XML exports, then compiled with GCC.
• Tooling: GitLab CI pipelines cross-compile firmware, run static analysis (cppcheck), and publish artifacts to an internal registry.

4. Determinism and Real-Time Behavior

I instrumented the firmware with GPIO toggles and measured jitter with a digital scope. Results:

• Cycle Time: 2 ms task executed within ±60 µs jitter under nominal load.
• Network Load: Enabling MQTT at QoS 1 increased jitter to ±120 µs; we mitigated by offloading MQTT to a secondary core.
• Interrupt Latency: Worst-case 8 µs when handling EtherCAT PDOs; acceptable for the machine’s servo loops.

5. Industrial Hardening Considerations

• Enclosure: DIN-rail carrier with conformal coating to handle humidity.
• Power: Dual redundant 24 VDC inputs with reverse polarity protection.
• Diagnostics: Added a dedicated UART console for maintenance and a secure bootloader supporting signed firmware updates.
• Cybersecurity: TPM 2.0 module for key storage, mutual TLS for MQTT, and remote attestation integrated with Azure DPS.

6. Integration with Existing Infrastructure

To avoid rewriting the HMI, we exposed the same OPC UA nodeset the original controller used. A translation layer mapped internal tags to OPC UA variables, and the existing SCADA system connected without changes.

7. Total Cost of Ownership

Break-even occurred in year three once the customer considered spares and reduced downtime. The intangible benefit: complete control over the roadmap and the ability to patch vulnerabilities on our own schedule.

8. Final Verdict

Custom RISC-V controllers are not a drop-in answer for every factory, but they shine when:

• You need specialized IO combinations or deterministic networking features.
• The organization is ready to treat control firmware like modern software with DevOps practices.
• Lifecycle cost and supply chain resilience outweigh the comfort of off-the-shelf PLCs.

For broader adoption, invest early in documentation, automated testing, and training maintenance staff. With those pillars in place, RISC-V can become a competitive differentiator in industrial automation programs.