Re: [avr-gcc-list] Howto I/O in asm instructions?]

[Dennis Clark]

  Do we _really_ have to go through such pain just to write some in-line
assembly in gcc?  THAT could sure use some streamlining in the avr-gcc
compiler.  In-line assembly is pretty much a must for embedded work.
Rather than do that I'll write assembly functions and link them in, this
is just too ugly to contemplate!

IMO,
DLC

> Ruud Vlaming schreef:
>> Hi,
>>
>> There are a couple of ways to use i/o address in assymbly.
>> Below i used a some:
>>
>> #define _EEARL_ "0x1E"
>> uint8_t portFSReadByte(unsigned char * pAddress)
>> { uint8_t result;
>>   asm volatile ( \
>>    "in   r26, __SREG__      \n\t"
>>    "cli                     \n\t"
>>    "out  %2, %A0            \n\t"
>>    "out  "_EEARL_", %B0     \n\t"
>>    "sbi  __EECR__, 0        \n\t"
>>    "in   %A0, 0x1D          \n\t"
>>    "out __SREG__, r26       \n\t"
>>    "" :"=r" (result) :"0" (pAddress), "I" (_SFR_IO_ADDR(EEARH)) : "r26"
>> );
>>   return result; }
>>
>> (1) You can define a constant, like i did for _EEARL_
>>   This is nice but no so portable.
>> (2) You can use the asm paramter list, like for EEARH
>>   Also nice, but errorprone, since i keep making mistakes in
>>   numbering, especially when you have many parameters and
>>   have to change something.
>> (3) The best thing to have would be something like __EECR__,
>>   resembling the definition for __SREG__, but that does not
>>   compile right now.
>>
>> Is the latter possible somehow? Or are there other solutions?
>
> You could go for option 2 if you use syntax like this (took this from
> eeprom.h)
>
>      __asm__ __volatile__ (
>          "/* START EEPROM WRITE CRITICAL SECTION */\n\t"
>          "in  r0, %[__sreg]           \n\t"
>          "cli                         \n\t"
>          "sbi %[__eecr], %[__eemwe]   \n\t"
>          "sbi %[__eecr], %[__eewe]    \n\t"
>          "out %[__sreg], r0           \n\t"
>          "/* END EEPROM WRITE CRITICAL SECTION */"
>          :
>          : [__eecr]  "i" (_SFR_IO_ADDR(EECR)),
>            [__sreg]  "i" (_SFR_IO_ADDR(SREG)),
>            [__eemwe] "i" (EEMWE),
>            [__eewe]  "i" (EEWE)
>          : "r0"
>      );
>
> This makes the code far more readable IMHO. For more info on the %[ ]
> notation take look at:
> http://gcc.gnu.org/onlinedocs/gcc-4.3.0/gcc/Extended-Asm.html
>
> HTH
>
> Wouter
>
>
>
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-- 
Dennis Clark
TTT Enterprises


-- 
Dennis Clark
TTT Enterprises