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.
