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|  How to reduce interrupt latency in embedded C for real-time performance?

How to reduce interrupt latency in embedded C for real-time performance?

October 14, 2024

Optimize real-time performance in embedded C with our guide. Learn strategies to reduce interrupt latency for firmware developers.

How to reduce interrupt latency in embedded C for real-time performance?

 

Minimize Interrupt Handler Code Size

 

  • One of the most immediate ways to reduce interrupt latency is to keep your interrupt service routines (ISRs) concise. Lengthy instructions increase execution time.
  • Offload any non-critical processing to the main loop or a separate software task. ISRs should handle only the most time-sensitive tasks.

 

Enable Global Interrupts Judiciously

 

  • Make sure global interrupts are enabled only where necessary. Disabling interrupts frequently increases overall latency, as queued interrupts wait until they can execute.
  • Prefer using local or peripheral-specific interrupt enables/disables over global disables.
void criticalTask() {
    // Save the Interrupt State
    uint8_t savedState = __save_interrupt_state();
    __disable_interrupt();
    
    // Critical code that can't be interrupted
    // ...

    // Restore the Interrupt State
    __restore_interrupt_state(savedState);
}

 

Use Appropriate Priority Levels

 

  • Properly configure interrupt priority levels to ensure that the most critical interrupts are processed first. This is usually available on systems with nested vectored interrupt controllers.
void configureInterruptPriorities() {
    setInterruptPriority(IRQ_TIMER, LOW_PRIORITY);
    setInterruptPriority(IRQ_UART, HIGH_PRIORITY);
}

 

Optimize Compiler Settings

 

  • Utilize your compiler's optimization flags to fine-tune how code is translated into machine code. Higher optimization can lead to smaller, faster binary figures, reducing latency.
  • Always test the end efficiency and functionality after changing optimization settings.

 

Implement Zero-Overhead Interrupts

 

  • On platforms that support it, configure zero-overhead or tail-chaining ISR, thereby reducing register save/restore times between interrupt exits and new entries.

 

Use Inline Functions for Fast Paths

 

  • Using inline functions in performance-critical paths can reduce the overhead introduced by function calls.
static inline int fastComputation(int a, int b) {
    return (a * b) + (a - b);
}

 

Employ Direct Memory Access (DMA)

 

  • Utilize DMA for high-speed data transfers to ensure CPU isn’t interrupted for large-volume data passing, allowing it to continue executing critical tasks.

 

Understand Your Hardware

 

  • Fully comprehend your microcontroller's architecture to exploit various features or hardware instruction sets that help minimize interrupt handling overhead.

 

Reduce Criticals in Shared Resource

 

  • Use lock-free algorithms and atomic operations wherever possible to avoid long critical sections in interrupt handlers, which increase wait times.
atomic_uint counter;

void incrementCounter() {
    atomic_fetch_add_explicit(&counter, 1, memory_order_relaxed);
}

 

Adjust each area appropriately in line with your specific hardware platform and firmware requirements to achieve significant improvements in interrupt latency. Experiment with a mix of these methods to facilitate an optimally tuned real-time system.

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