contrib/loaders/erase_check/stm8_erase_check.s

   1 /*
   2     Copyright (C) 2017 Ake Rehnman
   3     ake.rehnman(at)gmail.com
   4
   5     This program is free software: you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation, either version 3 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License
  16     along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18 ;;
  19 ;; erase check memory code
  20 ;;
  21  .org 0x0
  22 ;; start address
  23  start_addr: .byte 0x00
  24        .word 0x8000
  25 ;; byte count
  26  byte_cnt: .byte 0x00
  27        .word 0x8000
  28 ;
  29 ; SP must point to start_addr on entry
  30 ; first relocate start_addr to the location
  31 ; we are running at
  32 start:
  33         ldw X,SP
  34         ldw .cont+2,X
  35         ldw X,(start_addr+1,SP) ;start addr
  36         ldw Y,(byte_cnt+1,SP)   ;count
  37         ld A,#0xff
  38 ;
  39 ; if count == 0 return
  40 .L1:
  41         tnzw Y
  42         jrne .decrcnt   ;continue if low word != 0
  43         tnz (byte_cnt,SP)       ;high byte
  44         jreq .exit      ;goto exit
  45 ;
  46 ; decrement count (byte_cnt)
  47 .decrcnt:
  48         tnzw Y  ;low word count
  49         jrne .decr1
  50         dec (byte_cnt,SP)       ;high byte
  51 .decr1:
  52         decw Y; decr low word
  53 ;
  54 ; first check if [start_addr] is 0xff
  55 .cont:
  56         ldf A, [start_addr.e]
  57         cp A,#0xff
  58         jrne .exit ;exit if not 0xff
  59 ;
  60 ; increment start_addr (addr)
  61         incw X
  62         jrne .L1
  63         inc (start_addr,SP)     ;increment high byte
  64         jra .L1
  65 ;
  66 .exit:
  67         ldw (start_addr+1,SP),X ;start addr
  68         ldw (byte_cnt+1,SP),Y   ;count
  69         break