;;
  ;;  mur.sat
  ;;
  ;;  Somewhen in the year 20xx, 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) 2011-2015 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_TOD0 EQU H'00'
RTC_REG_TOD1 EQU H'01'
RTC_REG_TOD2 EQU H'02'
RTC_REG_TOD3 EQU H'03'
RTC_REG_ALM0 EQU H'04'
RTC_REG_ALM1 EQU H'05'
RTC_REG_ALM2 EQU H'06'
RTC_REG_CTL  EQU H'07'
RTC_REG_STAT EQU H'08'
RTC_REG_TCH  EQU H'09'

RTC_INIT_CTL EQU b'00001000'
;; RTC_INIT_TCH EQU b'10101011'    ; trickle charger enabled with diode and 4kohm
;; RTC_INIT_TCH EQU b'10101010'    ; trickle charger enabled with diode and 2kohm
RTC_INIT_TCH EQU b'10101001'    ; trickle charger enabled with diode and 250ohm
;; RTC_INIT_TCH EQU b'00001100'    ; trickle charger disabled

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

  movlw     RTC_ADDR_W
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     RTC_REG_STAT
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  call      i2c_restart

  movlw     RTC_ADDR_R
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  call      i2c_recv_byte
  call      i2c_nack

  btfsc     I2C_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     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     RTC_REG_TOD0
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     .7
  movwf     RTC_BYTE_CNT
rtc_init_clear
  clrw
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack
  decfsz    RTC_BYTE_CNT,f
  goto      rtc_init_clear

  movlw     RTC_INIT_CTL
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  clrw
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     RTC_INIT_TCH
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  call      i2c_stop
  return

  ;; ---------------
rtc_get_time
  movlw     RTC_TOD0
  movwf     FSR
  call      i2c_start

  movlw     RTC_ADDR_W
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     RTC_REG_TOD0
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  call      i2c_restart

  movlw     RTC_ADDR_R
  call      i2c_send_byte
  btfsc     I2C_BYTE,0
  goto      rtc_error_ack

  movlw     .4
  movwf     RTC_BYTE_CNT
rtc_get_time_loop
  call      i2c_recv_byte
  movf      I2C_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

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