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  ;;
  ;;  mur.sat
  ;;
  ;;  Somewhen in the year 2011, mur.at will have a nano satellite launched
  ;;  into a low earth orbit (310 km above the surface of our planet). The
  ;;  satellite itself is a TubeSat personal satellite kit, developed and
  ;;  launched by interorbital systems. mur.sat is a joint venture of mur.at,
  ;;  ESC im Labor and realraum.
  ;;
  ;;  Please visit the project hompage at sat.mur.at for further information.
  ;; 
  ;;
  ;;  Copyright (C) 2011 Christian Pointner <equinox@mur.at>
  ;;                         
  ;;  This file is part of mur.sat.
  ;;
  ;;  mur.sat is free software: you can redistribute it and/or modify
  ;;  it under the terms of the GNU General Public License as published by
  ;;  the Free Software Foundation, either version 3 of the License, or
  ;;  any later version.
  ;;
  ;;  mur.sat is distributed in the hope that it will be useful,
  ;;  but WITHOUT ANY WARRANTY; without even the implied warranty of
  ;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  ;;  GNU General Public License for more details.
  ;;
  ;;  You should have received a copy of the GNU General Public License
  ;;  along with mur.sat. If not, see <http://www.gnu.org/licenses/>.
  ;;
  ;; -------------------------------------
  ;; DEFINES
  ;;   constants
RTC_ADDR_W   EQU b'11010000'
RTC_ADDR_R   EQU b'11010001'
RTC_REG_SEC  EQU H'00'
RTC_REG_MIN  EQU H'01'
RTC_REG_HOUR EQU H'02'
RTC_REG_DOW  EQU H'03'
RTC_REG_DOM  EQU H'04'
RTC_REG_MON  EQU H'05'
RTC_REG_YEAR EQU H'06'
RTC_REG_A1S  EQU H'07'
RTC_REG_A1M  EQU H'08'
RTC_REG_A1H  EQU H'09'
RTC_REG_A1D  EQU H'0A'
RTC_REG_A2M  EQU H'0B'
RTC_REG_A2H  EQU H'0C'
RTC_REG_A2D  EQU H'0D'
RTC_REG_CON  EQU H'0E'
RTC_REG_STAT EQU H'0F'

  ;; -------------------------------------
i2c_start
  bsf       STATUS,RP0
  bcf       TRISB,RTC_SDA
  nop
  bcf       TRISB,RTC_SCL
  bcf       STATUS,RP0
  return
  
  ;; ------------------
i2c_restart
  bsf       STATUS,RP0
  bsf       TRISB,RTC_SDA
  nop
  bsf       TRISB,RTC_SCL
  nop
  nop
  nop
  bcf       TRISB,RTC_SDA
  nop
  bcf       TRISB,RTC_SCL
  bcf       STATUS,RP0
  return
  
  ;; ------------------
i2c_stop
  bsf       STATUS,RP0
  bsf       TRISB,RTC_SCL
  nop
  bsf       TRISB,RTC_SDA
  bcf       STATUS,RP0
  return
  
  ;; ------------------
i2c_send_byte
  movwf     RTC_BYTE
  movlw     .8
  movwf     RTC_BIT_CNT
  bsf       STATUS,RP0
i2c_send_byte_next
  btfss     RTC_BYTE,7
  bcf       TRISB,RTC_SDA
  btfsc     RTC_BYTE,7
  bsf       TRISB,RTC_SDA
  nop
  bsf       TRISB,RTC_SCL
  nop
  nop
  bcf       TRISB,RTC_SCL
  rlf       RTC_BYTE,f
  decfsz    RTC_BIT_CNT,f
  goto      i2c_send_byte_next

  nop
  nop
  bsf       TRISB,RTC_SDA
  bsf       TRISB,RTC_SCL
  bcf       STATUS,RP0
  movf      PORTB,w
  bsf       STATUS,RP0
  bcf       TRISB,RTC_SCL
  bcf       TRISB,RTC_SDA
  bcf       STATUS,RP0
  andlw     b'00010000'
  movwf     RTC_BYTE
  swapf     RTC_BYTE,f
  return

  ;; ------------------
i2c_recv_byte
  clrf      RTC_BYTE
  movlw     .8
  movwf     RTC_BIT_CNT
  bsf       STATUS,RP0
  bsf       TRISB,RTC_SDA
i2c_recv_byte_loop
  bsf       TRISB,RTC_SCL
  bcf       STATUS,RP0
  btfsc     PORTB,RTC_SDA
  bsf       RTC_BYTE,0
  bsf       STATUS,RP0
  bcf       TRISB,RTC_SCL
  decfsz    RTC_BIT_CNT,f
  goto      i2c_recv_byte_next

  bcf       TRISB,RTC_SDA
  bcf       STATUS,RP0
  return

i2c_recv_byte_next
  bcf       STATUS,C
  rlf       RTC_BYTE,f
  goto      i2c_recv_byte_loop

  ;; ------------------
i2c_ack
  bsf       STATUS,RP0
  bcf       TRISB,RTC_SDA
  bsf       TRISB,RTC_SCL
  nop
  nop
  bcf       TRISB,RTC_SCL
  bcf       STATUS,RP0
  return
  
  ;; ------------------
i2c_nack
  bsf       STATUS,RP0
  bsf       TRISB,RTC_SDA
  bsf       TRISB,RTC_SCL
  nop
  nop
  bcf       TRISB,RTC_SCL
  bcf       TRISB,RTC_SDA
  bcf       STATUS,RP0
  return

  ;; -------------------------------------
rtc_init
  call      i2c_start

  movlw     RTC_ADDR_W
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack
  
  movlw     RTC_REG_STAT
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack

  call      i2c_restart
  
  movlw     RTC_ADDR_R
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack

  call      i2c_recv_byte
  call      i2c_nack

  btfsc     RTC_BYTE,7
  goto      rtc_init_after_clock_fail
  
  call      i2c_stop
  return
  
rtc_init_after_clock_fail
  call      i2c_restart

  movlw     RTC_ADDR_W
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack
  
  movlw     RTC_REG_SEC
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack

  movlw     .16
  movwf     RTC_BYTE_CNT
rtc_init_clear
  clrw
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack
  decfsz    RTC_BYTE_CNT,f
  goto      rtc_init_clear

  call      i2c_stop
  return

  ;; ---------------
rtc_get_time
  call      i2c_start

  movlw     RTC_ADDR_W
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack
  
  movlw     RTC_REG_SEC
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack

  call      i2c_restart
  
  movlw     RTC_ADDR_R
  call      i2c_send_byte
  btfsc     RTC_BYTE,0
  goto      rtc_error_ack

  movlw     .7
  movwf     RTC_BYTE_CNT
rtc_get_time_loop
  call      i2c_recv_byte
  movf      RTC_BYTE,w
  movwf     INDF
  decfsz    RTC_BYTE_CNT,f
  goto      rtc_get_time_next

  call      i2c_nack
  call      i2c_stop
  return
  
rtc_get_time_next
  incf      FSR,f
  call      i2c_ack
  goto      rtc_get_time_loop

  ;; ---------------
rtc_error_ack
  call      i2c_stop
  ;; TODO: add error handling
  return

  ;; -------------------------------------