Is there a way to tell the compiler not to optimise a particular piece of code?

Question

Hi,
I am using nrf51822xxaa , Keil Uvision 5.14.2.1. SDK 10.0.0 and S130. I need optimisation level O3 for most parts of the code, except for one part (about 10 lines of code) which I need to be O0. Is it possible? If so, how to achieve this? Thanks.

Hieu · Accepted Answer

I have not tried it personally, but I see a overriding compiling option for each group in Keil. 
 You could put all such code in some files, then put all such files into a specific group and then adjust the compiling option of that group according to your wish. 
 Just want to update to include @awneil's helpful comments: 
 
 
 uVision also allows you to set per-file options. 
 This has nothing to do with Nordic; it is standard Keil operation - covered in the standard Keil documentation: 
 www.keil.com/.../uv4_ca_filegrp_att.htm 
 
 
 See also #pragma Onum 
 www.keil.com/.../armcc_chr1359124988971.htm

Is there a way to tell the compiler not to optimise a particular piece of code?

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