Compiler defined symbol not found from code

Question

I'm using AVR GCC compiler v5.4.0 under MPLAB X IDE v5.45. I defined a symbol for the compiler in the avr-as-pre section. It adds the following to the invoked command:

-DF_CPU=32000000UL

Inside the code I have some checks like this:

#ifndef F_CPU
    // do something

and it actually does something. It looks like if it doesn't find the symbol. Am I wrong about how to define a symbol for the whole project in this way?

UPDATE

The IDE calls this stuff "defined symbols":

but it stores them as "preprocessor macros" actually:

  <AVR-AS-PRE>
    <property key="announce-version" value="false"/>
    <property key="include-paths" value=""/>
    <property key="preprocessor-macros" value="F_CPU=32000000UL"/>
    <property key="preprocessor-macros-undefined" value=""/>
    <property key="suppress-warnings" value="false"/>
  </AVR-AS-PRE>

Unfortunately it seems it does not pass them to the compiler:

$ grep -nrw . -e F_CPU
./nbproject/configurations.xml:117:        <property key="preprocessor-macros" value="F_CPU=32000000UL"/>

That's the correct syntax, and it works fine in a test: godbolt.org/z/dxoxMa3rc. So probably the -D option is not actually making it to the compiler; I'm not familiar with this IDE so I'm not sure if where you've added this option is the right place. One note is that what you're defining is not a symbol (which is a name resolved to an address at link time) but rather a macro (which is only used in preprocessing); any chance that confusion is related? — Nate Eldredge
– Nate Eldredge, Commented Mar 28, 2021 at 16:42
@NateEldredge, I guess you're right. I've update the question. — Mark
– Mark, Commented Mar 29, 2021 at 4:44
Using the "avr-as-pre" section is suspect unless you actually have assembly-language files in your project. "avr-as" is the name of the GNU assembler for AVR. — David Grayson
– David Grayson, Commented Mar 29, 2021 at 18:34
@DavidGrayson, that makes sense. I was betrayed by the pre suffix - I guessed it stands for preprocessor but I didn't think about the as part! — Mark
– Mark, Commented Mar 29, 2021 at 18:48

Mark · Accepted Answer · 2021-03-29 08:17:34Z

3

You have to define the compiler symbols under avr-gcc > Preprocessing and messages > Defined symbols section:

answered Mar 29, 2021 at 8:17

Mark

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