Profile Execution Time of Interrupts Using DWT Cycle Counters on STM32F4

Using DWT Cycle Counters on STM32F4 to Profile Execution Time of Interrupt Service Routines

Profiling the execution time of Interrupt Service Routines (ISRs) is crucial for optimizing performance in embedded systems. The Data Watchpoint and Trace (DWT) unit in STM32F4 microcontrollers provides an easy way to measure cycle counts. This tutorial will guide you through the steps to set up and use the DWT cycle counters for profiling ISRs.

Prerequisites

• Basic understanding of STM32 microcontrollers and Cortex-M architecture.
• STM32F4 development board.
• STM32CubeIDE or any compatible IDE set up for STM32 development.
• Familiarity with writing C code for embedded systems.

Parts/Tools

• STM32F4 Development Board (e.g., Nucleo or Discovery).
• USB cable for programming the board.
• Computer with STM32CubeIDE installed.
• Basic electronic tools (soldering iron, multimeter, etc. if needed).

Steps

1. Set Up Your Development Environment
   • Open STM32CubeIDE and create a new STM32 project.
   • Select your STM32F4 microcontroller or development board.
   • Configure the project settings as required.
2. Enable DWT in Your Code
   • Include the necessary header files at the top of your main C file:

   #include "stm32f4xx.h"

   • Enable the DWT unit by ensuring the following code is executed in your main function:

   CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;

3. Implement the ISR
   • Define an ISR where you want to measure the execution time:

   void EXTI15_10_IRQHandler(void) {
                   // ISR code here
               }

4. Measure Execution Time
   • Use the DWT cycle count register to measure cycles:

   void EXTI15_10_IRQHandler(void) {
                   uint32_t start = DWT->CYCCNT; // Start counting
                   // ISR code
                   uint32_t end = DWT->CYCCNT; // End counting
                   uint32_t cycleCount = end - start; // Calculate cycles
               }

   • To ensure accurate measurements, reset the cycle counter before the ISR execution:

   DWT->CYCCNT = 0; // Reset counter

5. Compile and Upload Your Code
   • Build your project in STM32CubeIDE.
   • Connect your STM32 board to your computer and upload the code.
6. Analyze the Results
   • Use a debugger or print the cycle count to the console to analyze the ISR performance:

   printf("ISR Cycle Count: %lun", cycleCount);

Troubleshooting

• Cycle Count Not Resetting: Ensure that DWT is enabled and your code properly resets the counter before measurements.
• Unexpected Cycle Count Values: Verify that the ISR is not being interrupted by other ISRs. Use priority levels to manage interrupts.
• Debugging Issues: If using a debugger, make sure it supports DWT features. Some IDEs might have limitations.

Conclusion

Using DWT cycle counters on STM32F4 microcontrollers is an effective way to profile the execution time of ISRs. By following the steps outlined in this tutorial, you can successfully measure and analyze the performance of your ISRs, leading to more efficient code and better real-time system performance. Happy coding!