STM32 Interrupt latency test

Here is my quick Interrupt latency test for STM NUCLEO-F767ZI development board with Cortex-M7 CPU.

Quick Results - are quite good:

• 1st channel (Yellow) is just slowly blinking LED LD1 on PB0 port at toggle rate 10 Hz (frequency 5 Hz)
• 2nd channel tries to quickly toggle PE0 GPIO pin in main loop:

  while (1)
  {
      HAL_GPIO_TogglePin(GPIOE, GPIO_PIN_0); // Toggle PE0
  }

• where 1st channel is trigger and also Interrupt handler.

And Workspace file digilentad2/STM32-LED-Timer-And-Poll-HF.dwf3work

From Scope (Digilent Analog Discovery 2) we can see that:

• PE0 GPIO Output frequency is around 10 Mhz - so toggle rate is impressive 20 MHz
• Servicing interrupt takes around 1.32 micro-seconds - which is very good.

Why GPIO is not faster?

• according to DS11532 page 49:

  A fast I/O handling allows a maximum I/O toggling up to 108 MHz.

• but looking to RM0410 page 91, Table 7. Number of wait states according to CPU clock (HCLK) frequency

  The Program FLASH is capable to handle only up to 30 MHz without wait states. For 216 MHz there are at least 7 Wait states (8 CPU cycles)

  • you can find used latency in main.c on this line:

    if(HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_7) != HAL_OK)
    { /* ... */}

    • so here are set 7 WS (8 cycles)

• To solve this problem one has to:

  • move GPIO code from slow Flash to TC (Time Critical) RAM
  • access directly GPIO registers (this example calls HAL routines which has significant overhead)

• However my 100 MHz scope is unable to handle such speed so I have no plan to try it.

Setup

Required Hardware:

• STM NUCLEO-F767ZI development board with Cortex-M7 CPU. Ordered STM NUCLEO-F767ZI - Amazon.de

Recommended Hardware:

• Digilent Analog Discovery 2 scope + WaveForms 3 Software

Required Software:

• STM32CubeF7 Firmware package required to build this project. You need to download and unpack en.stm32cubef7_v1-17-0.zip first that download and unpack to same location - overwrite files patch archive en.stm32cubef7-v1-17-1.zip
• System Workbench for STM32 development IDE

Build

• First copy modified Src/main.c to your unpacked CubeF7 tree, for example:

  c:\Ac6\STM32Cube_FW_F7_V1.17.0\Projects\STM32F767ZI-Nucleo\Examples\TIM\TIM_TimeBase\Src
  

• Then run AC6 IDE
• Click on Import Existing Projects ...
• select Path like:

  c:\Ac6\STM32Cube_FW_F7_V1.17.0\Projects\STM32F767ZI-Nucleo\Examples\TIM\TIM_TimeBase\SW4STM32\STM32F767ZI-Nucleo
  

• Warning! All these examples use same project name STM32F767ZI-Nucleo, however Ac6 insists that Project name must be unique. So I recommend to rename this project right after import...

To generate assembler listing - ensure that you already build .elf binary and try:

cd Debug
c:\Ac6\SystemWorkbench\plugins\fr.ac6.mcu.externaltools.arm-none.win32_1.17.0.201812190825\tools\compiler\arm-none-eabi\bin\objdump.exe ^
  -S STM32F767ZI-Nucleo.elf > STM32F767ZI-Nucleo.lst

Resources

• Please see my Getting started with ST NUCLEO F767ZI Board for introduction.