;;
  ;;  spreadspace pic utils
  ;;
  ;;
  ;;  Copyright (C) 2011-2013 Christian Pointner <equinox@spreadspace.org>
  ;;
  ;;  This file is part of spreadspace pic utils.
  ;;
  ;;  spreadspace pic utils 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.
  ;;
  ;;  spreadspace pic utils 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 spreadspace pic utils. If not, see <http://www.gnu.org/licenses/>.
  ;;

#define INTPIN  PORTA,4
  
  ;; --- transmit byte and add it to csum
com_tx_byte
  movwf     SSPBUF
  bcf       INTPIN
  xorwf     csum,f
  bsf       STATUS,RP0
com_tx_byte_wait
  btfss     SSPSTAT,BF
  goto      com_tx_byte_wait
  bcf       STATUS,RP0
  movf      SSPBUF,w
  bsf       INTPIN
  return

  ;; ---- wait for byte to be received
com_rx_byte
  bsf       STATUS,RP0
  btfsc     SSPSTAT,BF
  goto      com_rx_got_byte
  bcf       STATUS,RP0
  btfss     SSPCON,SSPOV
  goto      com_rx_byte
  movf      SSPBUF,w
  bcf       SSPCON,SSPOV
  goto      com_rx_byte

com_rx_got_byte
  bsf       STATUS,RP0
  movf      SSPBUF,w
  return

  ;; ----- initialize com (not a subroutine, com_init is called by generic_init
com_init
  ;; bank 3
  bsf       STATUS,RP0
  bsf       STATUS,RP1
  bcf       ANSEL,ANS4          ; RA5/SS as digital input

  ;; bank 1
  bcf       STATUS,RP1
  movlw     b'01110000'         ; set internal OSC to 8MHz
  movwf     OSCCON
  movlw     b'01000000'         ; SMP=0,CKE=1
  movwf     SSPSTAT
  bcf       TRISC,5             ; RC5(SDO) = out
  bcf       INTPIN              ; interrupt line to master
  
  ;; bank 0
  bcf       STATUS,RP0
  movlw     b'00100100'         ; SSPEN=1,CKP=0,SSPM=0100(SPI Slave with SS)
  movwf     SSPCON
  bsf       INTPIN