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Author Topic: want to see assembly output from C++ compiler  (Read 1371 times)
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Hello everyone!  I am new to Arduino development, and I am very excited.  I want to say this is a wonderful introduction for me to the world of microcontrollers.  Based on this web site, I was able successfully to build my own Arduino board, program bootloader using my home-made parallel cable, then start writing my own software.  Now I have a board that receives Morse Code commands and replies with Morse Code.  (I'm willing to share my code if anyone is interested, by the way.)

Now, however, I'm wondering if I can save some space by re-writing some of the stuff using assembly language directly instead of C++.  I thought a good place to start would be to get the C++ compiler to emit assembly code so I could see which functions could be better coded in assembly by hand.  I did a "g++ --help" and found out that there is a compiler option "-save-temps" which is described as "Do not delete intermediate files".  I'm hoping one of those intermediate files is the assembly language output from the compiler (just a guess... maybe wishful thinking).

Can anyone tell me how to tweak the compiler options that is used by the Arduino IDE?

Thanks in advance,

- Don
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Actually, it looks like I was able to partially answer my own question.  Instead of modifying the compiler options to produce an assembly listing, I discovered that I can use objdump.exe (included in the Arduino distribution) to disassemble the object file that the compiler generated.  I'm using Windows, so I went into a command prompt, and added c:\arduino-0006 to my PATH:

    PATH=c:\arduino-0006;%path%

Then I went into the Applet directory beneath my project and ran objdump:

c:\arduino-0006\tools\avr\avr\bin\objdump.exe -x -d -S morse_buddy.cpp.o >morse_buddy.asm

This created my assembly listing, interspersed with the original C++ code.  This should give me a clue how to write my own embedded assembly code inside my C++ code.

I would still be interested in knowing how to tweak the compiler options, though, in case anybody knows... thanks!

- Don
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Right now, there's no way (short of editing its source code) to get the Arduino environment to pass arbitrary parameters to the C++ compiler.  You can only set a few options (e.g. CPU speed and microcontroller).  If there's enough demand for it, this is something that could be added to later versions of Arduino.
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It might not need to be an option... maybe just always emit assembly code annotated with the original C++ that produced it, as yet another file in the applet subdirectory beneath the project.  I doubt that would bother anybody... at worst, it would be ignored by some people.

At any rate, I am finding the use of objdump.exe very handy in figuring out how to make my code smaller.  It's also very useful for me to start learning how the Atmega8 processor works.
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