Re: [avr-gcc-list] In line assembly

[Graham Davies]

I'm not an expert, but below your message I have put a function with mixed C
and assembly that is working well for me.  You have to go read up on how C
uses the registers, how arguments are passed and results returned and which
registers you can do what with.  See FAQ 13 in the avr-libc documentation.
Note that I happen to know that my function waitSpmen() does not trash R24
and R25, otherwise I would not be able to call it where I do.  Anyway,
perhaps this will put you on the right track.

Graham.


----- Original Message ----- 
From: "Dinesh Kumar" <address@hidden>
To: <address@hidden>
Sent: Tuesday, July 06, 2004 11:46 PM
Subject: [avr-gcc-list] In line assembly

Hi Experts,
Im new to GCC for AVR. I need to use C and assembly together. I would like
to know how I can put in line assembly in GCC. Looks like 'pragma' is not
working.
Thanks in advance
Regards
Din



/***************************************************************************
****
 * Function readProgramMemory() - read a word (two bytes) from program
memory
 * (Flash) at a specified address.  The function argument is the byte
address
 * from which data is to be read.  The function returns the value at that
byte
 * address and the one after it packed in little-endian order into an
unsigned
 * short integer (16-bit word).
 *
 * This function is Copyright (C) 2004 Graham Davies, all rights reserved.
 */
static unsigned short readProgramMemory( unsigned short address )
{
   register unsigned short result asm( "r24" );

   waitSpmen();                   /* don't continue until SPMEN is clear */
   asm( "MOVW  R30, R24" );     /* move address to z pointer (R30,R31) */
   asm( "LPM" );                /* read first byte (to R0) */
   asm( "MOV   R24, R0" );      /* store as least significant byte */
   asm( "INC   R30" );          /* move up the address by one byte */
   asm( "LPM" );                /* read second byte */
   asm( "MOV   R25, R0" );      /* store as most significant byte */

   if ( address >= APP_END )
   {
      result = 0xAAAA;
   }

   return ( result );

} /* end of function readProgramMemory() */