72 lines
2.0 KiB
NASM
72 lines
2.0 KiB
NASM
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; Copyright (C) 2019 Christophe Meneboeuf <christophe@xtof.info>
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;
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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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;
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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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;
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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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; Must be the same as in memory.inc !!
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.define ZERO_2_1 $19
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.define ZERO_2_3 $1B
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.define ZERO_8_1 $D6
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.define ZERO_8_2 $D7
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.define FROM ZERO_2_1
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.define TO ZERO_2_3
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.define SIZEH ZERO_8_1
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.define SIZEL ZERO_8_2
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.export memcpy
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.export TXT1_LINES
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.DATA
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TXT1_LINES:
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.word $400, $480, $500, $580, $600, $680, $700, $780, $428, $4A8, $528, $5A8, $628, $6A8
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.word $728, $7A8, $450, $4D0, $550, $5D0, $650, $6D0, $750, $7D0
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.CODE
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; http://www.6502.org/source/general/memory_move.html
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; Move memory up
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;
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; FROM = source start address
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; TO = destination start address
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; SIZE = number of bytes to move
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;
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memcpy: LDX SIZEH ; the last byte must be moved first
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CLC ; start at the final pages of FROM and TO
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TXA
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ADC FROM+1
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STA FROM+1
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CLC
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TXA
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ADC TO+1
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STA TO+1
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INX ; allows the use of BNE after the DEX below
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LDY SIZEL
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BEQ MU3
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DEY ; move bytes on the last page first
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BEQ MU2
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MU1: LDA (FROM),Y
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STA (TO),Y
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DEY
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BNE MU1
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MU2: LDA (FROM),Y ; handle Y = 0 separately
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STA (TO),Y
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MU3: DEY
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DEC FROM+1 ; move the next page (if any)
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DEC TO+1
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DEX
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BNE MU1
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RTS |