Printf of a floating point in ARM and stack alignment

Technical Note 85413



9/11/2015 12:25 PM


In some cases, printf of floating point (%f) does not seem to work.


The IAR C/C++ Compiler for ARM requires the Stack Pointer to be aligned at 8 bytes. 8-byte alignment is required by AEABI (and some instructions generated by the compiler for some cores).

The default cstartup code automatically initializes the ARM core stack(s) to an 8-byte aligned address. Make sure that your application and/or RTOS also does this.


According to the MQX release notes, stack alignment is not ensured in MQX 3.7. The behavior is corrected in MQX 3.8. This problem has also been observed with other RTOSes.

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