[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [avr-gcc-list] Using __tmp_reg__ etc in assembly file

From: Georg-Johann Lay
Subject: Re: [avr-gcc-list] Using __tmp_reg__ etc in assembly file
Date: Fri, 23 Jan 2009 01:06:01 +0100
User-agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)

Colin Wall schrieb:
gcc gererates a header in easch assembly output that looks like

  .file   "fifo.c"
  .arch atmega168
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
  .global __do_copy_data
  .global __do_clear_bss
 ;  GNU C version 3.4.6 (avr)

No, it does not exist in any header. It exists in gcc ;-)


So, from what I can see, the compiler makes these defines available to
C source, but not to asm (.S) source, and I need to repeat them myself
in the asm file to use them there.

No, these defines are not available in a C source. They are available in a assembler .s source that is generated by the compiler.
So you can use this in your inline asm.

If you like make you can make the assembler source(s) dependent on a dummy header:

.INTERMEDIATE: asm-defines.h dummy.c

%.S: asm-defines.h

        touch $<

asm-defines.h: dummy.c
        avr-gcc -mmcu=$(MCU_TARGET) -S $< -o $@

and include the generated header in your files

#include "asm-defines.h"

in order to be always in sync with the compiler and the target.

You can make use of the constructions (examples):
   out  (_SFR_IO_ADDR(SREG)), r25
   out  (_SFR_IO_ADDR(SPL)), r26
   out  (_SFR_IO_ADDR(SPH)), r27
etc, if i remember correctly.
These work in the asm file because SREG etc are defined when io.h is included. I can't see a way to use __tmp_reg__ et al without re-defining
them myself.

This is just an asm file head. You cannot use __SREG__ et al. without redefining it or letting avr-gcc write a file like described above.

Note that SREG is different from __SREG__:

SREG from libc header expands to the RAM address.
__SREG__ from gcc output is set to the SFR address in I/O space.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]