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Hard Fault Demo on STM32L452 Nucleo-64 Board

This is a demo program to show a problem with the STM32L452 running code in SRAM2 which causes the program to end up (after a random amount of time, typically a couple of minutes) in the hard fault handler. This demo is designed to run on an STM32L452RE Nucleo-64 board.

There is a complementary demo for the SMT32L432 designed to run on an STM32L432KC Nucleo-32 board which shows that this problem does not occur on the STM32L43xx series MCUs.

Overview

This is an Eclipse project generated via STM32CubeMX. It uses FreeRTOS to spawn two threads. One thread blinks the green LED on the PCB at 1Hz. The other thread starts the ADC DMA process reading into a circular buffer at 26400 sps. These are placed on a message queue in the DMA interrupt. The thread then reads each block of these samples from the queue and sends them to a FIR filter running in SRAM2. The filter results are discarded.

There are 3 GPIOs defined:

  • ADC_STATUS (PA0)
  • FIR_STATUS (PA1)
  • ERROR (PC0)

ADC_STATUS will flip between high and low as the DMA moves between half-complete and complete.

FIR_STATUS will go high during FIR processing and low otherwise.

ERROR is raised in the hard fault handler.

This code will eventually end up in the hard fault handler, at which point ERROR is raised and the LED will blink at about 5Hz.

Versions of this code seems to run fine on an STM32L432KC Nucleo32 board and on a custom PCB using an STM32L433CCU6 chip. That same board will fail in the same manner when using an STM32L452CEU6. The code will run indefinitely when the FIR filter code is placed in Flash.

Placing Code in SRAM2

  1. The section "bss2" (yes, poorly named) is defined in the STM32L452RE_FLASH.ld linker script.
  2. Code and data in bss2 is copied to SRAM2 by the ./Src/startup_stm32l452xx.S startup code.
  3. The FIR filter code is placed in the bss2 section by modifying ./Drivers/CMSIS/Include/arm_math.h:
    void arm_fir_f32(
      const arm_fir_instance_f32 * S,
      float32_t * pSrc,
      float32_t * pDst,
      uint32_t blockSize) __attribute__((section(".bss2")));

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