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Memory Allocation Hangs in CMSIS RTOS Threads, FPU Enabled, and Memory Allocation for sprintf func

Associate III

Hi Community,

I'm currently facing a critical issue in my STM32 project involving FreeRTOS tasks, FPU (Floating-Point Unit) usage, and memory allocation for floating-point formatting. This problem has emerged after enabling FPU support and configuring project properties to accommodate floating-point operations.

Problem Overview:

My application relies heavily on FreeRTOS for task management, and recently I enabled FPU support to facilitate floating-point operations. However, upon attempting to format floating-point values with sprintf within FreeRTOS tasks, I encountered memory allocation hangs and failures. These issues occur consistently when utilizing memory allocation functions such as `malloc`, particularly within tasks involving floating-point formatting.

1. FPU Configuration: I've ensured that FPU support is properly enabled in my STM32 project, and I've configured project properties to accommodate floating-point operations.

2. Memory Allocation Hangs: The application hangs or encounters failures at memory allocation functions such as `pvPortMalloc` or `malloc`, specifically when attempting to format floating-point values within FreeRTOS tasks.

3. STM32_LOCK_BLOCK(): The application gets stuck at the `STM32_LOCK_BLOCK()` instruction within `__retarget_lock_init_recursive`, with the comment indicating /*Unable to allocate memory*/.


Have anyone encountered similar challenges with memory allocation in FPU-enabled STM32 projects, particularly when involving floating-point formatting with sprintf/snprintf within FreeRTOS tasks ?

Thank you.

Guillaume K
ST Employee


not sure it is related but if you use STM32CubeIDE with "newlib-nano" C library, there is an option to be checked to use printf and scanf with floats.

It's in the STM32CubeIDE project properties, in "C/C++ build"/ "Settings" / "tool settings" / "MCU settings", "use float with printf from newlib-nano ( -u _printf_float)"  (for STM32Cube 1.14.1)


Pavel A.
Evangelist III

@Guillaume K  Was there a regression with the locks in one of recent CubeIDE releases? Someone reported not long ago broken locks in the newlib. Is this fixed (if was broken) in the latest release?


Yes, I already configured it, but I think the problem is in the newlib_lock library, as I'm using the thread safe library