Using printf() with FreeRTOS sometimes causes hardfaults

[skygreenslade]

I am working on using FreeRTOS for a project, and have implemented printf() debugging by redirecting it to a uart. This works great most of the time, and is very helpful for FreeRTOS debugging, as FreeRTOS_printf() and FreeRTOS_debug_printf() will leverage this functionality.

Unfortunately, it seems to cause hard faults frequently, but not in every case. 

One call that consistently caused a hard fault was 

FreeRTOS_printf( ( "FreeRTOS_connect: %u to %xip:%u\n", [...]);

Another one I had to manually remove was

FreeRTOS_debug_printf( ( "Socket %u -> [%s]:%u State %s->%s\n", [...]);

I came across a previous post which seemed to have a similar issue, but it appeared to have been resolved. 

Is there more configuration that I need to implement to have this work in every case? Or is there something else I am missing?

Some more details about my implementation:

I am using CubeMX to generate my code

I am using OpenOCD and GCC

My printf implementation uses the following code

#ifdef __GNUC__
#   define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#   define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */

PUTCHAR_PROTOTYPE
{
    HAL_UART_Transmit(&huart3, (uint8_t *)&ch, 1, 0xFFFF);

    return ch;
}

 Thanks for reading, any insight is appreciated!

[Chris21]

Perhaps the stack of the task calling printf is overflowing.

[nouirakh · Accepted solution]

Hello @skygreenslade 

Could you please verify that you give the task that's calling FreeRTOS_printf() enough stack space. Printing functions often use a lot of stack space to format the string.

[AMars.4]

Are you calling the print function from multiple tasks? I use a print from multiple tasks with no issues, maybe try something like below:

static void debugPrintUART(const char *pData);


void myprintf(const char *fmt, ...)
{
  if(osMutexAcquire(debugPrint_MutexHandle, osWaitForever) == osOK)
  {
    static char buffer[256];
    va_list args;
    va_start(args, fmt);
    vsnprintf(buffer, sizeof(buffer), fmt, args);
    va_end(args);

    debugPrintUART(buffer);
    osMutexRelease(debugPrint_MutexHandle);
  }
}

static void debugPrintUART(const char *pData)
{
  HAL_UART_Transmit(&huart1, (uint8_t*)&pData[0], strlen(pData), 100);
}

Or you could have the debug print in a single task, and have the other tasks just message this one to do the print.. this may actually be a better alternative.

Task stack size maybe an issue as others mention.

[skygreenslade]

It appears that this was the problem. Increasing my stack size has resolved the issue, thanks for everyone's help!

[unsigned_char_array]

Could you tell us what exact stack size you used before and what you have now? This can help others with the same problem in the future. Thanks in advance.

[skygreenslade]

I haven't yet determined the minimum stack size required for the task that was the problem. It will depend on the application how big it needs to be, so I don't want to claim that a specific size will work.

As for the previous size, it had somehow been changed back to the default that CubeMX generates: 128 * 4.