70 lines
1.6 KiB
ArmAsm
70 lines
1.6 KiB
ArmAsm
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/*
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Copyright (C) 2017 Ake Rehnman
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ake.rehnman(at)gmail.com
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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;;
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;; erase check memory code
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;;
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.org 0x0
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;; start address
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start_addr: .byte 0x00
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.word 0x8000
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;; byte count
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byte_cnt: .byte 0x00
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.word 0x8000
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;
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; SP must point to start_addr on entry
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; first relocate start_addr to the location
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; we are running at
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start:
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ldw X,SP
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ldw .cont+2,X
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ldw X,(start_addr+1,SP) ;start addr
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ldw Y,(byte_cnt+1,SP) ;count
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ld A,#0xff
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;
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; if count == 0 return
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.L1:
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tnzw Y
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jrne .decrcnt ;continue if low word != 0
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tnz (byte_cnt,SP) ;high byte
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jreq .exit ;goto exit
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;
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; decrement count (byte_cnt)
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.decrcnt:
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tnzw Y ;low word count
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jrne .decr1
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dec (byte_cnt,SP) ;high byte
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.decr1:
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decw Y; decr low word
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;
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; first check if [start_addr] is 0xff
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.cont:
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ldf A, [start_addr.e]
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cp A,#0xff
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jrne .exit ;exit if not 0xff
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;
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; increment start_addr (addr)
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incw X
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jrne .L1
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inc (start_addr,SP) ;increment high byte
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jra .L1
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;
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.exit:
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ldw (start_addr+1,SP),X ;start addr
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ldw (byte_cnt+1,SP),Y ;count
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break
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