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can coprocessor instruction be produced by compiler from c code

Note: This was originally posted on 18th April 2013 at http://forums.arm.com

can accessing coprocessor instruction be produced by compiler from c code？

except float point instructions?

such like drain write buffer instruction?

any docs describe detail of this?

rensheng yang over 12 years ago

Note: This was originally posted on 19th April 2013 at http://forums.arm.com

i know this feature, named register.

i mean compiler translate c code to arm instructions. except this extension of c code added by specific compiler, can normal c code produce instructions like 'MCR'?

etc, we write
int a;
int b;
int c=a+b;

this will translate to load and modify instructions. or we can use hard-float to control translate to float instructions.

how we can control coprocessor instructions produced from normall C code express?

i think usually c code is used for moving data, so may not produce control instructions, is this right? any theory?
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Scott Douglass over 12 years ago

Note: This was originally posted on 22nd April 2013 at http://forums.arm.com

What is your goal here? Is it
a: to make the compiler emit certain coprocessor instructions? (If yes, please give an example)
or
b: to make sure the compiler *does not* emit any coprocessor instructions? (If yes, why?)
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Martin Weidmann over 12 years ago

Note: This was originally posted on 18th April 2013 at http://forums.arm.com

Which compiler?

If you are using armcc, I'd probably use the "named register" feature. This lets you declare a variable and tie to a coprocessor register (or other kind of register). Then whenever you access the variable the compiler will generate suitable coprocessor instructions. So:

egister unsigned int cp15_control __asm("cp15:0:c1:c0:0");

This ties the variable to the coprocessor register "cp15:0:c1:c0:0".

http://infocenter.arm.com/help/topic/com.arm.doc.dui0491i/CJAHJDBG.html

I believe GCC has a similar feature, but not sure of the syntax.
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