Re: SPR access

[David Brown <david at westcontrol dot com>]

Hi,

No problem - helping out is one way users can contribute to the gcc
community, to save the gcc developers a little effort.

Next time, however, keep questions like this on the gcc-help mailing
list - it is for asking for help with using gcc.  The gcc@gcc.gnu.org
mailing list is for development of the compiler itself.

mvh.,

David


On 13/07/16 16:39, tutruong0412@gmail.com wrote:
> Hi,
> 
> Thank you for your answer.
> It is very useful for me.
> 
> Best regards;
> 
> Truong TT
> 
>> On Jul 8, 2016, at 11:07 PM, David Brown <david@westcontrol.com> wrote:
>>
>> Hi,
>>
>> (You have something wrong with your emails - the subject for your post
>> had a copy of most of the body of the email.  I have changed it to
>> something smaller.)
>>
>> You can't use a function argument for the number of the SPR, because the
>> assembler requires the SPR at assembly time to generate the full mtspr
>> instruction.  My solution was to use a macro for this, rather than a
>> function (even a static inline function won't work):
>>
>> #define readSpr(sp) ({ uint32_t res; \
>>        asm volatile (" mfspr %[res], %[spr] " : \
>>        [res] "=r" (res) : \
>>        [spr] "i" (sp) ); \
>>        res; })
>>
>> #define writeSpr(sp, va) \
>>        asm volatile (" mtspr %[spr], %[val] " : \
>>        : \
>>        [spr] "i" (sp), [val] "r" (va) )
>>
>>
>> mvh.,
>>
>> David
>>
>>
>>
>>> On 08/07/16 16:16, Tran Tu Truong wrote:
>>> Dear Mr/Ms;
>>>
>>> I am Truong, working at Vietnam human engineering in Vietnam.
>>> Now, I am using D32 Design Studio for programming MPC5777C micro
>>> controller (GNU C Compiler 4.9). I've already made a sample inline asm
>>> code in .C file ase bellow:
>>> void set_spr ( uint32_t spr_num, uint32_t val )
>>> {
>>> asm volalatile ("mtspr %0, %1"
>>> :
>>> :"r"(spr_num), "r"(val)
>>> );
>>> }
>>> This code does not work correct (It should work but not work). I found
>>> out the constraints operands [:"r"(spr_num),] is not correct. I thinks
>>> it better if spr_num is be referred as a constant not a register ( ex:
>>> mtspr 120, val ). But I don't know how to revise.
>>> I also referred on
>>> https://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints
>>> about PowerPC but I cannot understand clearly.So, could you please
>>> help me to explain about that?
>>> If you have the instruction about "constraints for asm operands" for
>>> MPC5777C micro controller, please provide me.
>>>
>>> Thank you.
>>> --Tran Tu Truong--
>>