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ARM: Warning L6989W


Information in this knowledgebase article applies to:

  • MDK-ARM V5.16 and Later

SYMPTOM

I am using the STM32L476 and I an getting warning L6989W when using some math functions or DSP library functions. For example, when I build a project using the arm_fir_f32() filter functions, I get the following warning:

 Warning: L6989W: Could not apply patch sdcomp-29491-629360 to instruction VPOP
{d8-d15} at offset 0x48e, instruction is within an IT block and is not the last
instruction for arm_fir_f32.o (.text).

How do I resolve this warning? Can I ignore it?

CAUSE

Some members of the STM32L4 family have an eratta for the FMC (Flexible Memory Controller) where a read burst access of 9 words or more is not supported by FMC. To prevent burst accesses that are greater than 8 words, a special linker patch was developed to patch certain instructions that result in burst accesses of greater than 8 words. The patch can be applied in most cases with a few exceptions. One of these exceptions is when the instruction to be patched is inside an IT (If-Then) block and is not the last instruction in that block. In this case this warning will be generated.

RESOLUTION

Since the FMC is only used for external memory, you can ignore this warning if you are only using internal memory. If you are using external memory, make sure your stack is located on-chip. In compiled code, the use of IT blocks can be eliminated by using the --no_conditionalize compiler option. If you are using the DSP library, you will need to rebuild it with the --no_conditionalize compiler option to prevent this warning.This can increase the processing time for DSP functions, so this should only be done for the library used with the STM32L4xx. Also, some math functions such as log10() contain IT blocks that cannot be patched. Since these math functions are not available to be re-built, it may be difficult to eliminate the warning in all cases. In the case of log10(), you can use a similar function, log10f() that does not have the IT block restriction.

STATUS

Please Contact ST Microelectronics to get the latest status of this eratta

MORE INFORMATION

SEE ALSO

FORUM THREADS

The following Discussion Forum threads may provide information related to this topic.

Last Reviewed: Thursday, August 18, 2016


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