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|  How to Fix Long Interrupt Service Routines: Step-by-Step Guide

How to Fix Long Interrupt Service Routines: Step-by-Step Guide

October 14, 2024

Optimize firmware with our guide to fix long interrupt service routines in C. Follow the step-by-step process to enhance performance efficiently.

How to Fix Long Interrupt Service Routines: Step-by-Step Guide

 

Analyze the Current Interrupt Service Routine (ISR)

  • Identify and list down all the ISRs in your firmware. Understanding which ones are causing delays is crucial.
  • Use profiling tools to measure the execution time of each ISR. Aim to find any ISR that exceeds a reasonable duration.
  • Inspect the source code for each ISR to understand its complexity and logic flow.

 

Minimize Critical Sections

  • Reduce the amount of code executed within Critical Sections. These are often block sections of code in an ISR where no other code can run.
  • Avoid the use of mutexes or other locking mechanisms inside ISRs. Locking mechanisms can introduce significant delays.
  • If necessary, refactor critical sections by moving code out of the ISR where possible.

 

Offload Tasks to Background Processing

  • Identify tasks executed within the ISR that do not require immediate execution. Move these tasks to the main loop or a lower priority task.
  • Implement a simple message queue or a buffer where the ISR can place data for the main loop to process later.
  • Use flags or events to signal the main loop that data processing is required outside the ISR.

 

Use Interrupt Prioritization

  • Assign priorities to ISRs so that the most critical interrupts are processed first.
  • By using the hardware's natural prioritization capabilities, ensure your system remains responsive.
  • Balance priorities to avoid interrupt starvation, where less critical interrupts are never serviced.

 

Optimize ISR Code

  • Ensure that your compiler optimization settings are appropriate for ISR code to reduce execution time.
  • Refactor and simplify complex logic within ISRs. Avoid loops or recursive function calls.
  • Utilize inline functions instead of standard function calls to reduce overhead time.
  • Make use of volatile keyword for variables shared between ISRs and other code to prevent optimization issues.

 

Use Interrupt Vectors Wisely

  • Directly manipulate hardware registers in ISRs when needed, instead of using higher-level abstractions which can be slower.
  • Ensure that ISR vectors are correctly configured in your vector table, avoiding unnecessary ISR calls.

 

Test and Validate Changes

  • After making changes to the ISR, perform thorough testing to ensure the modifications haven’t introduced new issues.
  • Use hardware-debugging tools to monitor ISR execution times and check for unintended behavior.
  • Continuously measure and log ISR durations to ensure they meet your performance criteria.

 

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