eerd_byte.S

/* Copyright (c) 2009  Dmitry Xmelkov
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

   * Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in
     the documentation and/or other materials provided with the
     distribution.
   * Neither the name of the copyright holders nor the names of
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   POSSIBILITY OF SUCH DAMAGE.  */

/* $Id$ */

#ifndef __DOXYGEN__

#include <avr/io.h>

#if E2END && __AVR_ARCH__ > 1

#include <avr/eeprom.h>
#include "asmdef.h"
#include "eedef.h"

/* uint8_t eeprom_read_byte (uint8_t EEMEM *addr);
 */

#define ret_lo  r24
#define ret_hi  r25

ENTRY   eeprom_read_byte

#if __AVR_XMEGA__   /* -------------------------------------------- */

    rcall   eeprom_mapen
    ld  ret_lo, Z
    clr ret_hi
    ret

ENTRY   eeprom_mapen

  ; It has to be noted that for some Xmega parts (Eg. Xmega E family) EEPROM
  ; is always memory mapped. So it is not required to  enable EEPROM mapping
  ; explicitly. 
  ; The presence of NVM_EEMAPEN_bm macro (from the part header file) can be
  ; checked to find out whether the device supports enabling/disabling of
  ; EEPROM mapping. Absence of NVM_EEMAPEN_bm could be interpreted safely as
  ; EEPROM always memory mapped and explicit memory mapping of EEPROM is not 
  ; required/invalid.
#if     defined (NVM_EEMAPEN_bm)
  ; Load base address of NVM.
    ldi ZL, lo8(NVM_BASE)
    ldi ZH, hi8(NVM_BASE)

  ; Wait until NVM is not busy.
1:  ldd r19, Z + NVM_STATUS - NVM_BASE
    sbrc    r19, NVM_NVMBUSY_bp
    rjmp    1b

  ; Enable EEPROM mapping into data space.
    ldd r19, Z + NVM_CTRLB - NVM_BASE
    ori r19, NVM_EEMAPEN_bm
    std Z + NVM_CTRLB - NVM_BASE, r19
#endif

  ; Load Z with correct EEPROM address to read from data space.
    movw    ZL, addr_lo
    subi    ZL, lo8(-MAPPED_EEPROM_START)
    sbci    ZH, hi8(-MAPPED_EEPROM_START)

    ret

#else           /* -------------------------------------------- */

1:  sbic    _SFR_IO_ADDR (EECR), EEWE
    rjmp    1b
# ifdef  EEARH
#  if     E2END > 0xFF
    out _SFR_IO_ADDR (EEARH), addr_hi
#  else
    ; This is for chips like ATmega48: the EEAR8 bit must be cleaned.
    out _SFR_IO_ADDR (EEARH), __zero_reg__
#  endif
# endif
    out _SFR_IO_ADDR (EEARL), addr_lo
    sbi _SFR_IO_ADDR (EECR), EERE
    clr ret_hi
    in  ret_lo, _SFR_IO_ADDR (EEDR)
    ret

#endif          /* -------------------------------------------- */

ENDFUNC

#endif  /* E2END && __AVR_ARCH__ > 1 */
#endif  /* !__DOXYGEN__ */