[okl4-developer] Problem with inline assembler on arm926ejs

[Lukas HANEL]

Hi Gabi,

thanks for your help. But in fact I am not the author of the problematic
code and I do not have in mind to understand or debug it. The code comes
from the 1.5.2 release and does not compile, so I was addressing the
OKL4 support to provide a correct version.

My first attempt was of course to understand and possible correct the
problem. But as I don't know what the function is supposed to do and how
it tries to achieve it and when not even finding what the _(xx) syntax
means, I was giving up and directing me to the list.

I find the following reference very enlightning:
Brennan's Guide to Inline Assembly
http://www.delorie.com/djgpp/doc/brennan/brennan_att_inline_djgpp.html

Gabi Voiculescu wrote:
> Personally I would use another way to write this (use zero as an
> output register instead of passing it as clobber stuff to the GCC,
> notice how many ':' I use)
>
> static inline void sleep(void)
> {
> #if defined(__GNUC__)
> word_t zero = 0;
> __asm__ __volatile__ (
> " mcr p15, 0, %0 , c7, c0, 4 \n" /* Wait for interrupt */
> : "=r" (zero) );
> #endif
> }
>
> Incidentally, I think you got that error because you used "_(zero)"
> instead of  "(zero)".
>
> I recommend for you to also look at the following source to explain
> the how to on GCC inline assembly for ARM:
> http://www.ethernut.de/en/documents/arm-inline-asm.html
>
>
> Gabi Voiculescu
>
>
> */Lukas HANEL <lukas.hanel at st.com>/* wrote:
>
>     Hi
>
>     I am trying to port OKL4 to a platform based on the arm926ejs core.
>     Therefore I copied the xscale platform folder and changed the
>     tools/machines.py to be based on an other processor architecture.
>     E.g.
>     < class pxa(xscale):
>     > class pxa(arm926ejs):
>
>     Trying to compile this gave me an error related to cryptic inline
>     assembler code.
>     However it seems, that the same code is working in other files, so
>     I am
>     confused.
>     The problem occures in arm926ejs/cpu.h, but nearly the same code
>     is used
>     in arm926ejs/cache.h
>     A similar syntax can be found in cache.h of other architectures.
>     Do you have a good reference for the inline assembly language?
>
>     Thanks
>     Lukas
>
>     Listing:
>     ~/okl4_release_1.5.2nhk$ ./tools/build.py machine=nhk15 project=iguana
>     example=naming simulate --debug=presub
>     scons: Reading SConscript files ...
>     Warn: No serial driver configured, not building serial server
>     SERIAL_DRIVER is uart_8250
>     scons: done reading SConscript files.
>     scons: Building targets ...
>     [CXX ] build/pistachio/l4kernel/object/src/cache.o
>     In file included from platform/pxa/pistachio/include/plat/timer.h:92,
>     from arch/arm/pistachio/include/arch/config.h:377,
>     from pistachio/include/config.h:146,
>     from pistachio/include/l4.h:70,
>     from pistachio/src/cache.cc:65:
>     arch/arm/pistachio/cpu/arm926ejs/include/cpu/cpu.h: In static member
>     function `static void arm_cpu::sleep()':
>     arch/arm/pistachio/cpu/arm926ejs/include/cpu/cpu.h:99: error: expected
>     `)' before "_"
>     arch/arm/pistachio/cpu/arm926ejs/include/cpu/cpu.h:97: warning: unused
>     variable 'zero'
>     scons: *** [build/pistachio/l4kernel/object/src/cache.o] Error 1
>     scons: building terminated because of errors.
>
>     arch/arm/pistachio/cpu/arm926ejs/include/cpu/cpu.h:
>     static inline void sleep(void)
>     {
>     word_t zero = 0;
>     __asm__ __volatile__ (
>     " mcr p15, 0, "_(zero)", c7, c0, 4 ;" /* Wait for
>     interrupt */
>     #if defined(__GNUC__)
>     :: [zero] "r" (zero)
>     #endif
>     );
>     }
>
>
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