Accessing local variables from assembly

Mateja Putic11728

I'm working with the F2618 on CCSv4.0.1.01001

Here's my code:

void myFunc( void )
{
   int foo;
   asm(" .var foo");
   asm(" movx.w &foo, r12");
   asm(" movx.w r2, 0(r12)");

// Do something with foo
}

Basically I am trying to copy the SR to foo. How can I make sure 'foo' shows up in the symbol table so that the assembler can find it, .var is not working.

Many Thanks,

Mateja

over 16 years ago

0 Mateja Putic11728 over 16 years ago

Intellectual 275 points

I have also tried .global but foo isn't a global so that shouldn't work either. Perhaps I'm missing a linker option?

0 Joerg Quinten over 16 years ago

Guru 17650 points

Hi Mateja,

have a look at this app note which explains mixing C with assembler (http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slaa140). What do you intend to do with the Status register?

Rgds
aBUGSworstnightmare

0 Mateja Putic11728 over 16 years ago in reply to Joerg Quinten

Intellectual 275 points

Yes, I am definitely familiar with this documentation, but I still haven't been able to figure it out. Another relevant source would be Appendix D. of the FET manual.

Perhaps you are right in asking the big picture question -- I am porting Contiki from mspgcc to CCS and this particular bit of code masks all maskable interrupts and returns the GIE bit in the SR. Can I access the SR from C? The assembly routine that I wrote up is supposed to copy the address of a local variable to let's say R12, then copy the value of the SR to this address, then return 'foo & GIE'. I suppose all this could be avoided if I knew how to access the SR from C, and ideas?

Whether I need it to port this bit of code, though, I would still like to know how to access a local variable from assembly, just for my own edification.

Thanks again,

Mateja

0 Joerg Quinten over 16 years ago in reply to Mateja Putic11728

Guru 17650 points

Hi Mateja,

did you have a look at the Compilers Users Manual? There is an Instrinsic which calls '__get_SR_register(void);' (refer to http://focus.ti.com/lit/ug/slau132c/slau132c.pdf ;page 109) -> so, what about using this?
Rgds
aBUGSworstnightmare

0 Mateja Putic11728 over 16 years ago in reply to Joerg Quinten

Intellectual 275 points

Brilliant! That's it. You actually solved a bunch of issues for me with this, because I'm porting the low-level context switching / memory allocation code and it uses a lot of intrinsics.

Thanks a bunch.

Mateja

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Accessing local variables from assembly