Whether you’re building control software for a brushless DC motor (BLDC), PMSM, or induction machine, efficient motor code development is the cornerstone of robust, responsive, and safe performance. At the heart of real-time motor control lies a tight loop of functions executed every pulse-width modulation (PWM) cycle, typically in the range of 10 to 100 microseconds. Here’s a comprehensive breakdown of the core principles of efficient algorithm design and the key timer-based functions you must get right.

A Word of Caution from Experience

Over the years, I have overseen numerous embedded developers—brilliant individuals who have achieved remarkable engineering feats. But one pattern emerges far too often: developers hacking their way to a working product.

This approach may deliver results in the short term, but it is detrimental to long-term product maintenance and scalability. Without a strategy, the code becomes a liability—hard to document, debug, optimize, or hand off.

That’s why these principles matter. They provide a strategic blueprint not only for building efficient code but also for self-documenting architectures that make debugging, testing, and extending far easier.

ARM Cortex-M and Timer-Based Execution

It is also essential to recognize that nearly all modern microcontrollers used in motor control—whether from STMicroelectronics, Texas Instruments, NXP, Infineon, or Renesas—are built upon ARM Cortex-M cores, such as M0+, M3, M4, or M7. Despite differences in peripherals and tooling, they all operate on a timer-driven architecture that is fundamentally the same.

That means these principles are broadly applicable and portable across platforms. Once you master timer-based control on one Cortex-M-based MCU, transitioning to another vendor’s platform becomes significantly easier.

1. Real-Time Determinism (Timer Functions)

Motor control software must operate within strict time constraints. Each iteration of your control loop must finish before the next PWM cycle begins.

Tips:

• Use timer-based interrupts to enforce deterministic execution.
• Offload slower tasks, such as logging and communication, to background threads or processes.
• Profile and monitor loop execution time constantly.

2. Modular Software Architecture

Good software architecture is modular and clear.
Best Practices:

• Separate core functions: Control logic, sensing, estimation, PWM generation, and safety.
• Implement state machines for operating modes like INIT, RUN, FAULT, and STOP.
• Keep platform-specific and generic code separate for easier portability.

3. Efficient Use of MCU Resources
Today’s MCUs are packed with tools—use them wisely.

Tips:

• Utilize hardware accelerators like MAC units, CORDIC, and DSP extensions.
• Implement DMA for ADC and serial data to minimize CPU usage.
• Choose between fixed-point or floating-point math based on your processor.

4. Accurate Current Sensing

Current feedback is the foundation of high-performance control loops.

Efficiency Tips:

• Synchronize ADC sampling with PWM to reduce switching noise.
• Use dual-shunt or inline sensing for better resolution.
• Calibrate sensor offset and gain in real-time.

5. Position Estimation (Timer-Based Function)
Whether sensorless or sensored, accurate rotor position is non-negotiable.

Optimization Ideas:

• Utilize sliding-mode observers or phase-locked loop (PLL) algorithms for sensorless estimation.
• Leverage lookup tables or fixed-point math to reduce load.
• Apply low-latency filters that preserve dynamic response

6. Speed Estimation (Timer-Based Function)

Rotor speed is critical for FOC and other advanced control methods.

Efficiency Tips:

• Derive speed using Δθ/Δt or frequency-domain estimation.
• Use smoothing filters (exponential, IIR) to stabilize readings.
• Optimize for the MCU’s math capabilities.

7. PI Loop Processing (Timer-Based Function)

Your motor’s behavior is only as good as your control loop design.

Tips:

• Implement cascaded control (inner current loop, outer speed/position).
• Pre-compute constants to save cycles.
• Apply anti-windup clamping to prevent instability.

8. Duty Cycle Computation (Timer-Based Function)

This is where control signals become real motion.

Best Practices:

• Use SVPWM or sine-PWM for smooth, efficient torque production.
• Compute sin/cos using CORDIC or lookup tables for speed.
• Keep math efficient using fixed-point if float is too slow.

9. Error Detection & Response (Timer-Based Function)

Motor faults can be catastrophic—design to detect and react fast.

Efficiency Tips:

• Monitor for overvoltage, undervoltage, overcurrent, sensor failure, and other potential issues.
• Use ISR-based detection for speed and reliability.
• Build a robust state machine for safe shutdowns and recovery.

10. Testing, Tuning & Maintenance

Your firmware isn’t finished until it has been thoroughly tested, tuned, and validated.

Best Practices:

• Use live tuning tools via UART, CAN, or USB.
• Enable firmware updates through bootloaders or OTA.
• Perform Hardware-in-the-Loop (HIL) testing where possible.

Bonus Optimization Tips

• Execution Time Profiling: Always confirm your loop fits in the PWM cycle.
• Interrupt Prioritization: Time-critical code should have higher priority.
• Compiler and DSP Optimization: Enable optimization flags and utilize hardware DSP.
• Code Portability: Maintain clear and maintainable abstraction layers.

Final Thoughts

Efficient motor code isn’t just about making it work—it’s about making it reliable, fast, safe, and scalable. By combining a sound architecture with robust timer-based loop execution, you ensure the performance your application demands—whether it’s for drones, e-bikes, HVAC systems, or industrial drives.

These keys don’t just deliver performance—they also provide clarity, maintainability, and peace of mind. Strategy should not be an afterthought—it should be the core of your firmware.

And with virtually all motor control MCUs based on ARM Cortex-M cores, these principles will carry over from one project to the next, no matter the silicon vendor.

Need help implementing or tuning your motor control algorithms? Let’s talk!