# eewr_byte.S

/* Copyright (c) 2009  Dmitry Xmelkov

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"

ENTRY   eeprom_write_byte
mov     r18, r22

ENTRY   eeprom_write_r18

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

# ifndef CCP_IOREG_gc
#  define CCP_IOREG_gc  0xD8    /* IO Register Protection       */
# endif
# endif
# endif
# ifndef NVM_CMD_ERASE_WRITE_EEPROM_PAGE_gc
#  define NVM_CMD_ERASE_WRITE_EEPROM_PAGE_gc    0x35
# endif
# ifndef  NVM_CMD_ERASE_EEPROM_BUFFER_gc
#  define NVM_CMD_ERASE_EEPROM_BUFFER_gc        0x36
# endif

#if    ! defined (NVM_EEMAPEN_bm)
; Saving X register because it might contain source address of block
push XL
push XH
#endif

; Prepare 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

; It has to be noted that for some Xmega parts (Eg. Xmega E family) EEPROM
; is always memory mapped. So it is not possible to disable 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)
; Disable EEPROM mapping into data space.
ldd     r19, Z + NVM_CTRLB - NVM_BASE
andi    r19, ~NVM_EEMAPEN_bm
std     Z + NVM_CTRLB - NVM_BASE, r19

; Check the clearance of EEPROM page buffer.
ldd     r19, Z + NVM_STATUS - NVM_BASE
rjmp    3f                      ; erase is not required

; Note that we have only four clock cycles to write to the CCP
; protected register NVM_CTRLA, after writing to CCP.  The 'ldi'
; instruction always takes one clock to execute and 'std' instruction takes
; two clock cycles.  We fall within the four cycles that the CCP leaves
; us to write the command execution start bit to the NVM_CTRLA
; register.  Note that r18 must be preserved until written to NVM_DATA0

; Issue EEPROM Buffer Erase:
ldi     r19, NVM_CMD_ERASE_EEPROM_BUFFER_gc
std     Z + NVM_CMD - NVM_BASE, r19
ldi     r19, CCP_IOREG_gc
out     CCP, r19
ldi     r19, NVM_CMDEX_bm
std     Z + NVM_CTRLA - NVM_BASE, r19

; Wait until NVM is not busy.
2:      ldd     r19, Z + NVM_STATUS - NVM_BASE
sbrc    r19, NVM_NVMBUSY_bp
rjmp    2b

; Issue EEPROM Buffer Load command.
std     Z + NVM_CMD - NVM_BASE, r19
#endif
std     Z + NVM_ADDR2 - NVM_BASE, __zero_reg__
#if     defined (NVM_EEMAPEN_bm)
std     Z + NVM_DATA0 - NVM_BASE, r18
#else
subi    XL, lo8(-MAPPED_EEPROM_START)
sbci    XH, hi8(-MAPPED_EEPROM_START)
st      X, r18
#endif

; Issue EEPROM Erase & Write command.
ldi     r18, NVM_CMD_ERASE_WRITE_EEPROM_PAGE_gc
std     Z + NVM_CMD - NVM_BASE, r18
ldi     r18, CCP_IOREG_gc
ldi     r19, NVM_CMDEX_bm
out     CCP, r18
std     Z + NVM_CTRLA - NVM_BASE, r19

#if    ! defined (NVM_EEMAPEN_bm)
; Restoring X register
pop XH
pop XL
#endif

ret

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

rjmp    1b

# if     defined (EEPM0) && defined (EEPM1)
; Set programming mode: erase and write.
# elif   defined (EEPM0) || defined (EEPM1)
#  error        /* Unknown EECR register.       */
# endif

# ifdef  EEARH
#  if     E2END > 0xFF
#  else
; This is for chips like ATmega48: the EEAR8 bit must be cleaned.
#  endif
# endif
cli