Cannot use printf with floats on a Cube generated System Workbench project for STM32F429i discovery board.

[davidregan9]

Used cube to generate a project with default settings for STM32F429I disco board plus CMSIS V2 RTOS and USART 2 half duplex transmit only . Generated the code for System Workbench.

I retargeted _write() and provided __io_putchar(). I added -u _printf_float to the linker flags.

In the StartDefaultTask I added

 float fVal = 345.678;

 printf("Hello World\r\n");

 printf("fVal %f\r\n",fVal);

Output

Hello World

fVal . !

Issues

With -specs = nosys.specs -specs= nano.specs -u _printf_float - printf causes a hard fault.

With specs = nosys.specs -specs -u _printf_float - 1st printf OK 2nd printf produces incorrect output

[Dave Nadler]

See: http://www.nadler.com/embedded/newlibAndFreeRTOS.html

If you're using an RTOS, probably your printf with %f is failing because printf internally tries to malloc a buffer and fails.

Let us know if that's the issue please!

[Michael98006]

When I had issues with snprintf() under FreeRTOS, I increased heap and stack allocation as well as task stack size (by a factor of 10x from the original size), and the issue was resolved.

[Dave Nadler]

@davidregan9​ - Was this any help? Did you get your issue fixed? Please let us know,

Thanks, Best Regards, Dave

[davidregan9]

Hi Dave

I am still having issues.

I tested the return values of the printf which was a positive value (albeit wrong).

No errno was set.

I have been trying to isolate the issue. Without RTOS it works

[davidregan9]

BTW Increasing heap/stack made no difference.

[Dave Nadler]

@davidregan9​ - Can you confirm you are using:

• FreeRTOS?
• newlib and gcc?

If yes to both, your problem will definitely be solved using code here: http://www.nadler.com/embedded/newlibAndFreeRTOS.html

Please let us know, Thanks, Best Regards, Dave

[davidregan9]

@Dave Nadler​ I am using FreeRTOS 10.2.1; GCC ARM Embedded Toolchain 8 2019-q3-update and newlib (I assume since I removed -specs=nano.specs)

[Dave Nadler]

@davidregan9​ You are using newlib (or newlib-nano).

Use the code/instructions on my web page and it will solve your problem.

If the page isn't clear PLEASE let me know how to improve it.

Thanks, Best Regards, Dave

[davidregan9]

@Dave Nadler​ I will try it out and let you know. Thank you