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https://github.com/cc65/cc65.git
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Added a macro package for writing self modyfying code. By Christian Krüger.
git-svn-id: svn://svn.cc65.org/cc65/trunk@5536 b7a2c559-68d2-44c3-8de9-860c34a00d81
This commit is contained in:
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parent
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509
asminc/opcodes.inc
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509
asminc/opcodes.inc
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@ -0,0 +1,509 @@
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; opcodes.inc
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; ca65 6502 - opcode definitions, mainly for self modifying code
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;
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; Christian Krüger, latest change: 18-Sep-2010
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;
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; This software is provided 'as-is', without any expressed or implied
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; warranty. In no event will the authors be held liable for any damages
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; arising from the use of this software.
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;
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; Permission is granted to anyone to use this software for any purpose,
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; including commercial applications, and to alter it and redistribute it
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; freely, subject to the following restrictions:
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;
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; 1. The origin of this software must not be misrepresented; you must not
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; claim that you wrote the original software. If you use this software
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; in a product, an acknowledgment in the product documentation would be
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; appreciated but is not required.
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; 2. Altered source versions must be plainly marked as such, and must not
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; be misrepresented as being the original software.
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; 3. This notice may not be removed or altered from any source
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; distribution.
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;
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; Opcode-Table
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; ------------
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; Post fix explanation:
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; imm = #$00
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; zp = $00
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; zpx = $00,X
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; zpy = $00,Y
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; izp = ($00)
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; izx = ($00,X)
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; izy = ($00),Y
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; abs = $0000
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; abx = $0000,X
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; aby = $0000,Y
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; ind = ($0000)
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; iax = ($0000,X)
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; rel = $0000 (PC-relative) (supressed here)
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.macpack cpu
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OPC_BRK = $00
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OPC_ORA_izx = $01
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OPC_ORA_zp = $05
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OPC_ASL_zp = $06
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OPC_PHP = $08
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OPC_ORA_imm = $09
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OPC_ASL = $0A
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OPC_ORA_abs = $0D
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OPC_ASL_abs = $0E
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OPC_BPL = $10
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OPC_ORA_izy = $11
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OPC_ORA_zpx = $15
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OPC_ASL_zpx = $16
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OPC_CLC = $18
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OPC_ORA_aby = $19
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OPC_ORA_abx = $1D
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OPC_ASL_abx = $1E
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OPC_JSR_abs = $20
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OPC_AND_izx = $21
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OPC_BIT_zp = $24
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OPC_AND_zp = $25
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OPC_ROL_zp = $26
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OPC_PLP = $28
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OPC_AND_imm = $29
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OPC_ROL = $2A
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OPC_BIT_abs = $2C
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OPC_AND_abs = $2D
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OPC_ROL_abs = $2E
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OPC_BMI = $30
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OPC_AND_izy = $31
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OPC_AND_zpx = $35
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OPC_ROL_zpx = $36
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OPC_SEC = $38
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OPC_AND_aby = $39
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OPC_AND_abx = $3D
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OPC_ROL_abx = $3E
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OPC_RTI = $40
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OPC_EOR_izx = $41
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OPC_EOR_zp = $45
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OPC_LSR_zp = $46
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OPC_PHA = $48
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OPC_EOR_imm = $49
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OPC_LSR = $4A
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OPC_JMP_abs = $4C
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OPC_EOR_abs = $4D
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OPC_LSR_abs = $4E
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OPC_BVC = $50
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OPC_EOR_izy = $51
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OPC_EOR_zpx = $55
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OPC_LSR_zpx = $56
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OPC_CLI = $58
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OPC_EOR_aby = $59
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OPC_EOR_abx = $5D
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OPC_LSR_abx = $5E
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OPC_RTS = $60
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OPC_ADC_izx = $61
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OPC_ADC_zp = $65
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OPC_ROR_zp = $66
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OPC_PLA = $68
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OPC_ADC_imm = $69
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OPC_ROR = $6A
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OPC_JMP_ind = $6C
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OPC_ADC_abs = $6D
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OPC_ROR_abs = $6E
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OPC_BVS = $70
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OPC_ADC_izy = $71
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OPC_ADC_zpx = $75
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OPC_ROR_zpx = $76
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OPC_SEI = $78
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OPC_ADC_aby = $79
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OPC_ADC_abx = $7D
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OPC_ROR_abx = $7E
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OPC_STA_izx = $81
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OPC_STY_zp = $84
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OPC_STA_zp = $85
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OPC_STX_zp = $86
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OPC_DEY = $88
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OPC_TXA = $8A
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OPC_STY_abs = $8C
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OPC_STA_abs = $8D
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OPC_STX_abs = $8E
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OPC_BCC = $90
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OPC_STA_izy = $91
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OPC_STY_zpx = $94
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OPC_STA_zpx = $95
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OPC_STX_zpy = $96
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OPC_TYA = $98
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OPC_STA_aby = $99
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OPC_TXS = $9A
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OPC_STA_abx = $9D
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OPC_LDY_imm = $A0
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OPC_LDA_izx = $A1
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OPC_LDX_imm = $A2
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OPC_LDY_zp = $A4
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OPC_LDA_zp = $A5
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OPC_LDX_zp = $A6
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OPC_TAY = $A8
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OPC_LDA_imm = $A9
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OPC_TAX = $AA
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OPC_LDY_abs = $AC
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OPC_LDA_abs = $AD
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OPC_LDX_abs = $AE
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OPC_BCS = $B0
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OPC_LDA_izy = $B1
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OPC_LDY_zpx = $B4
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OPC_LDA_zpx = $B5
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OPC_LDX_zpy = $B6
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OPC_CLV = $B8
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OPC_LDA_aby = $B9
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OPC_TSX = $BA
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OPC_LDY_abx = $BC
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OPC_LDA_abx = $BD
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OPC_LDX_aby = $BE
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OPC_CPY_imm = $C0
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OPC_CMP_izx = $C1
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OPC_CPY_zp = $C4
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OPC_CMP_zp = $C5
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OPC_DEC_zp = $C6
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OPC_INY = $C8
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OPC_CMP_imm = $C9
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OPC_DEX = $CA
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OPC_CPY_abs = $CC
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OPC_CMP_abs = $CD
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OPC_DEC_abs = $CE
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OPC_BNE = $D0
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OPC_CMP_izy = $D1
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OPC_CMP_zpx = $D5
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OPC_DEC_zpx = $D6
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OPC_CLD = $D8
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OPC_CMP_aby = $D9
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OPC_CMP_abx = $DD
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OPC_DEC_abx = $DE
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OPC_CPX_imm = $E0
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OPC_SBC_izx = $E1
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OPC_CPX_zp = $E4
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OPC_SBC_zp = $E5
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OPC_INC_zp = $E6
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OPC_INX = $E8
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OPC_SBC_imm = $E9
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OPC_NOP = $EA
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OPC_CPX_abs = $EC
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OPC_SBC_abs = $ED
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OPC_INC_abs = $EE
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OPC_BEQ = $F0
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OPC_SBC_izy = $F1
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OPC_SBC_zpx = $F5
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OPC_INC_zpx = $F6
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OPC_SED = $F8
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OPC_SBC_aby = $F9
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OPC_SBC_abx = $FD
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OPC_INC_abx = $FE
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.if (.cpu .bitand ::CPU_ISET_65SC02)
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; OPC_NOP = $02 ; doublet
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; OPC_NOP = $03 ; doublet
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OPC_TSB_zp = $04
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; OPC_NOP = $0B ; doublet
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OPC_TSB_abs = $0C
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OPC_ORA_izp = $12
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; OPC_NOP = $13 ; doublet
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OPC_TRB_zp = $14
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OPC_INC = $1A
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; OPC_NOP = $1B ; doublet
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OPC_TRB_abs = $1C
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; OPC_NOP = $22 ; doublet
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; OPC_NOP = $23 ; doublet
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; OPC_NOP = $2B ; doublet
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OPC_AND_izp = $32
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; OPC_NOP = $33 ; doublet
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OPC_BIT_zpx = $34
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OPC_DEC = $3A
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; OPC_NOP = $3B ; doublet
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OPC_BIT_abx = $3C
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; OPC_NOP = $42 ; doublet
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; OPC_NOP = $43 ; doublet
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; OPC_NOP = $44 ; doublet
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; OPC_NOP = $4B ; doublet
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OPC_EOR_izp = $52
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; OPC_NOP = $53 ; doublet
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; OPC_NOP = $54 ; doublet
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; OPC_NOP = $5A ; doublet
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; OPC_NOP = $5B ; doublet
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OPC_EOR_abx = $5C
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; OPC_NOP = $62 ; doublet
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; OPC_NOP = $63 ; doublet
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OPC_STZ_zp = $64
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; OPC_NOP = $6B ; doublet
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OPC_ADC_izp = $72
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; OPC_NOP = $73 ; doublet
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OPC_STZ_zpx = $74
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OPC_PLY = $7A
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; OPC_NOP = $7B ; doublet
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OPC_JMP_iax = $7C
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OPC_BRA = $80
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; OPC_NOP = $82 ; doublet
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; OPC_NOP = $83 ; doublet
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OPC_BIT_imm = $89
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; OPC_NOP = $8B ; doublet
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OPC_STA_izp = $92
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; OPC_NOP = $93 ; doublet
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; OPC_NOP = $9B ; doublet
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OPC_STZ_abs = $9C
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OPC_STZ_abx = $9E
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; OPC_NOP = $A3 ; doublet
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; OPC_NOP = $AB ; doublet
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OPC_LDA_izp = $B2
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; OPC_NOP = $B3 ; doublet
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; OPC_NOP = $BB ; doublet
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; OPC_NOP = $C2 ; doublet
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; OPC_NOP = $C3 ; doublet
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; OPC_NOP = $CB ; doublet
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OPC_CMP_izp = $D2
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; OPC_NOP = $D3 ; doublet
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; OPC_NOP = $D4 ; doublet
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OPC_PHX = $DA
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; OPC_NOP = $DB ; doublet
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; OPC_NOP = $DC ; doublet
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; OPC_NOP = $E2 ; doublet
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; OPC_NOP = $E3 ; doublet
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; OPC_NOP = $EB ; doublet
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OPC_SBC_izp = $F2
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; OPC_NOP = $F3 ; doublet
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; OPC_NOP = $F4 ; doublet
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OPC_PLX = $FA
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; OPC_NOP = $FB ; doublet
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; OPC_NOP = $FC ; doublet
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.if (.cpu .bitand ::CPU_ISET_65C02)
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; bit instructions for 65C02
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OPC_RMB0 = $07
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OPC_RMB1 = $17
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OPC_RMB2 = $27
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OPC_RMB3 = $37
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OPC_RMB4 = $47
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OPC_RMB5 = $57
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OPC_RMB6 = $67
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OPC_RMB7 = $77
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OPC_SMB0 = $87
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OPC_SMB1 = $97
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OPC_SMB2 = $A7
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OPC_SMB3 = $B7
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OPC_SMB4 = $C7
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OPC_SMB5 = $D7
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OPC_SMB6 = $E7
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OPC_SMB7 = $F7
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OPC_BBR0 = $0F
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OPC_BBR1 = $1F
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OPC_BBR2 = $2F
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OPC_BBR3 = $3F
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OPC_BBR4 = $4F
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OPC_BBR5 = $5F
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OPC_BBR6 = $6F
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OPC_BBR7 = $7F
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OPC_BBS0 = $8F
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OPC_BBS1 = $9F
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OPC_BBS2 = $AF
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OPC_BBS3 = $BF
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OPC_BBS4 = $CF
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OPC_BBS5 = $DF
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OPC_BBS6 = $EF
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OPC_BBS7 = $FF
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.else
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; no bit instructions for 65SC02
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; OPC_NOP = $07 ; doublet
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; OPC_NOP = $17 ; doublet
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; OPC_NOP = $27 ; doublet
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; OPC_NOP = $37 ; doublet
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; OPC_NOP = $47 ; doublet
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; OPC_NOP = $57 ; doublet
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; OPC_NOP = $67 ; doublet
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; OPC_NOP = $77 ; doublet
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; OPC_NOP = $87 ; doublet
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; OPC_NOP = $97 ; doublet
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; OPC_NOP = $A7 ; doublet
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; OPC_NOP = $B7 ; doublet
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; OPC_NOP = $C7 ; doublet
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; OPC_NOP = $D7 ; doublet
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; OPC_NOP = $E7 ; doublet
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; OPC_NOP = $F7 ; doublet
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; OPC_NOP = $0F ; doublet
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; OPC_NOP = $1F ; doublet
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; OPC_NOP = $2F ; doublet
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; OPC_NOP = $3F ; doublet
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; OPC_NOP = $4F ; doublet
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; OPC_NOP = $5F ; doublet
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; OPC_NOP = $6F ; doublet
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; OPC_NOP = $7F ; doublet
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; OPC_NOP = $8F ; doublet
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; OPC_NOP = $9F ; doublet
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; OPC_NOP = $AF ; doublet
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; OPC_NOP = $BF ; doublet
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; OPC_NOP = $CF ; doublet
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; OPC_NOP = $DF ; doublet
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; OPC_NOP = $EF ; doublet
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; OPC_NOP = $FF ; doublet
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.endif
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.elseif (.cpu .bitand ::CPU_ISET_6502X)
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; stable, undocumented opcodes
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; OPC_KIL = $02 ; unstable
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OPC_SLO_izx = $03
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OPC_NOP_zp = $04
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OPC_SLO_zp = $07
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OPC_ANC_imm = $0B
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OPC_NOP_abs = $0C
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OPC_SLO_abs = $0F
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; OPC_KIL = $12 ; unstable
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OPC_SLO_izy = $13
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OPC_NOP_zpx = $14
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OPC_SLO_zpx = $17
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;OPC_NOP = $1A
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OPC_SLO_aby = $1B
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OPC_NOP_abx = $1C
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OPC_SLO_abx = $1F
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; OPC_KIL = $22 ; unstable
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OPC_RLA_izx = $23
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OPC_RLA_zp = $27
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OPC_ANC_imm = $2B
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OPC_RLA_abs = $2F
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; OPC_KIL = $32 ; unstable
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OPC_RLA_izy = $33
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OPC_NOP_zpx = $34
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OPC_RLA_zpx = $37
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; OPC_NOP = $3A ; doublet
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OPC_RLA_aby = $3B
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OPC_NOP_abx = $3C
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OPC_RLA_abx = $3F
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; OPC_KIL = $42 ; unstable
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OPC_SRE_izx = $43
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OPC_NOP_zp = $44
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OPC_SRE_zp = $47
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OPC_ALR_imm = $4B
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OPC_SRE_abs = $4F
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; OPC_KIL = $52 ; unstable
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OPC_SRE_izy = $53
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OPC_NOP_zpx = $54
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OPC_SRE_zpx = $57
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; OPC_NOP = $5A ; doublet
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OPC_SRE_aby = $5B
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OPC_NOP_abx = $5C
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OPC_SRE_abx = $5F
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; OPC_KIL = $62
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OPC_RRA_izx = $63
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OPC_NOP_zp = $64
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OPC_RRA_zp = $67
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OPC_ARR_imm = $6B
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OPC_RRA_abs = $6F
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; OPC_KIL = $72
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OPC_RRA_izy = $73
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OPC_NOP_zpx = $74
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OPC_RRA_zpx = $77
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; OPC_NOP = $7A ; doublet
|
||||
OPC_RRA_aby = $7B
|
||||
OPC_NOP_abx = $7C
|
||||
OPC_RRA_abx = $7F
|
||||
|
||||
OPC_NOP_imm = $80
|
||||
; OPC_NOP_imm = $82 ; doublet
|
||||
OPC_SAX_izx = $83
|
||||
OPC_SAX_zp = $87
|
||||
; OPC_NOP_imm = $89 ; doublet
|
||||
; OPC_XAA = $8B ; unstable
|
||||
OPC_SAX_abs = $8F
|
||||
|
||||
; OPC_KIL = $92 ; unstable
|
||||
; OPC_AHX_izy = $93 ; unstable
|
||||
OPC_SAX_zpy = $97
|
||||
; OPC_TAS_aby = $9B ; unstable
|
||||
; OPC_SHY_abx = $9C ; unstable
|
||||
; OPC_SHX_aby = $9E ; unstable
|
||||
; OPC_AHX_aby = $9F ; unstable
|
||||
|
||||
OPC_LAX_izx = $A3
|
||||
OPC_LAX_zp = $A7
|
||||
; OPC_LAX_imm = $AB ; unstable
|
||||
OPC_LAX_abs = $AF
|
||||
|
||||
; OPC_KIL = $B2 ; unstable
|
||||
OPC_LAX_izy = $B3
|
||||
OPC_LAX_zpy = $B7
|
||||
OPC_LAS_aby = $BB
|
||||
OPC_LAX_aby = $BF
|
||||
|
||||
; OPC_NOP_imm = $C2 ; doublet
|
||||
OPC_DCP_izx = $C3
|
||||
OPC_DCP_zp = $C7
|
||||
OPC_AXS_imm = $CB
|
||||
OPC_DCP_abs = $CF
|
||||
|
||||
; OPC_KIL = $D2 ; unstable
|
||||
OPC_DCP_izy = $D3
|
||||
OPC_NOP_zpx = $D4
|
||||
OPC_DCP_zpx = $D7
|
||||
OPC_NOP_DA = $DA
|
||||
OPC_DCP_aby = $DB
|
||||
OPC_NOP_abx = $DC
|
||||
OPC_DCP_abx = $DF
|
||||
|
||||
; OPC_NOP_imm = $E2 ; doublet
|
||||
OPC_ISC_izx = $E3
|
||||
OPC_ISC_zp = $E7
|
||||
; OPC_SBC_imm = $EB ; doublet
|
||||
OPC_ISC_abs = $EF
|
||||
|
||||
; OPC_KIL = $F2 ; unstable
|
||||
OPC_ISC_izy = $F3
|
||||
OPC_NOP_zpx = $F4
|
||||
OPC_ISC_zpx = $F7
|
||||
OPC_NOP_FA = $FA
|
||||
OPC_ISC_aby = $FB
|
||||
OPC_NOP_abx = $FC
|
||||
OPC_ISC_abx = $FF
|
||||
|
||||
.endif
|
||||
249
asminc/smc.mac
Normal file
249
asminc/smc.mac
Normal file
@ -0,0 +1,249 @@
|
||||
; smc.mac
|
||||
; ca65 Macro-Pack for Self Modifying Code (SMC)
|
||||
;
|
||||
; (c) Christian Krüger, latest change: 09-Nov-2011
|
||||
;
|
||||
; This software is provided 'as-is', without any expressed or implied
|
||||
; warranty. In no event will the authors be held liable for any damages
|
||||
; arising from the use of this software.
|
||||
;
|
||||
; Permission is granted to anyone to use this software for any purpose,
|
||||
; including commercial applications, and to alter it and redistribute it
|
||||
; freely, subject to the following restrictions:
|
||||
;
|
||||
; 1. The origin of this software must not be misrepresented; you must not
|
||||
; claim that you wrote the original software. If you use this software
|
||||
; in a product, an acknowledgment in the product documentation would be
|
||||
; appreciated but is not required.
|
||||
; 2. Altered source versions must be plainly marked as such, and must not
|
||||
; be misrepresented as being the original software.
|
||||
; 3. This notice may not be removed or altered from any source
|
||||
; distribution.
|
||||
;
|
||||
|
||||
.define _SMCDesignator .mid(0, .tcount(label) - 1, label) .ident(.concat(.string(.right(1, label)), "_SMC"))
|
||||
.define _SMCAlias .mid(0, .tcount(alias) - 1, alias) .ident(.concat(.string(.right(1, alias)), "_SMC"))
|
||||
.define SMC_AbsAdr $FADE
|
||||
.define SMC_ZpAdr $00
|
||||
.define SMC_Opcode nop
|
||||
.define SMC_Value $42
|
||||
|
||||
.macro SMC_OperateOnValue opcode, label
|
||||
opcode _SMCDesignator+1
|
||||
.endmacro
|
||||
|
||||
.macro SMC_OperateOnLowByte opcode, label
|
||||
SMC_OperateOnValue opcode, label
|
||||
.endmacro
|
||||
|
||||
.macro SMC_OperateOnHighByte opcode, label
|
||||
opcode _SMCDesignator + 2
|
||||
.endmacro
|
||||
|
||||
.macro SMC_Import alias
|
||||
.import _SMCAlias
|
||||
.endmacro
|
||||
|
||||
.macro SMC_Export alias, label
|
||||
.export _SMCAlias := _SMCDesignator
|
||||
.endmacro
|
||||
|
||||
.macro SMC label, statement
|
||||
_SMCDesignator: statement
|
||||
.endmacro
|
||||
|
||||
.macro SMC_TransferOpcode label, opcode, register
|
||||
.if .paramcount = 2 .or .match ({register}, a)
|
||||
lda #opcode
|
||||
sta _SMCDesignator
|
||||
.elseif .match ({register}, x)
|
||||
ldx #opcode
|
||||
stx _SMCDesignator
|
||||
.elseif .match ({register}, y)
|
||||
ldy #opcode
|
||||
sty _SMCDesignator
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_LoadOpcode label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
lda _SMCDesignator
|
||||
.elseif .match ({register}, x)
|
||||
ldx _SMCDesignator
|
||||
.elseif .match ({register}, y)
|
||||
ldy _SMCDesignator
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_StoreOpcode label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
sta _SMCDesignator
|
||||
.elseif .match ({register}, x)
|
||||
stx _SMCDesignator
|
||||
.elseif .match ({register}, y)
|
||||
sty _SMCDesignator
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_ChangeBranch label, destination, register
|
||||
.if .paramcount = 2 .or .match ({register}, a)
|
||||
lda #(destination - _SMCDesignator -2)
|
||||
sta _SMCDesignator+1
|
||||
.elseif .match ({register}, x)
|
||||
ldx #(destination - _SMCDesignator - 2)
|
||||
stx _SMCDesignator+1
|
||||
.elseif .match ({register}, y)
|
||||
ldy #(destination - _SMCDesignator - 2)
|
||||
sty _SMCDesignator+1
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_TransferValue label, value, register
|
||||
.if .paramcount = 2 .or .match ({register}, a)
|
||||
lda value
|
||||
sta _SMCDesignator+1
|
||||
.elseif .match ({register}, x)
|
||||
ldx value
|
||||
stx _SMCDesignator+1
|
||||
.elseif .match ({register}, y)
|
||||
ldy value
|
||||
sty _SMCDesignator+1
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_LoadValue label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
lda _SMCDesignator+1
|
||||
.elseif .match ({register}, x)
|
||||
ldx _SMCDesignator+1
|
||||
.elseif .match ({register}, y)
|
||||
ldy _SMCDesignator+1
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_StoreValue label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
sta _SMCDesignator+1
|
||||
.elseif .match ({register}, x)
|
||||
stx _SMCDesignator+1
|
||||
.elseif .match ({register}, y)
|
||||
sty _SMCDesignator+1
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
|
||||
.macro SMC_TransferLowByte label, value, register
|
||||
SMC_TransferValue label, value, register
|
||||
.endmacro
|
||||
|
||||
.macro SMC_LoadLowByte label, register
|
||||
SMC_LoadValue label, register
|
||||
.endmacro
|
||||
|
||||
.macro SMC_StoreLowByte label, register
|
||||
SMC_StoreValue label, register
|
||||
.endmacro
|
||||
|
||||
.macro SMC_TransferHighByte label, value, register
|
||||
.if .paramcount = 2 .or .match ({register}, a)
|
||||
lda value
|
||||
sta _SMCDesignator+2
|
||||
.elseif .match ({register}, x)
|
||||
ldx value
|
||||
stx _SMCDesignator+2
|
||||
.elseif .match ({register}, y)
|
||||
ldy value
|
||||
sty _SMCDesignator+2
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_LoadHighByte label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
lda _SMCDesignator+2
|
||||
.elseif .match ({register}, x)
|
||||
ldx _SMCDesignator+2
|
||||
.elseif .match ({register}, y)
|
||||
ldy _SMCDesignator+2
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_StoreHighByte label, register
|
||||
.if .paramcount = 1 .or .match ({register}, a)
|
||||
sta _SMCDesignator+2
|
||||
.elseif .match ({register}, x)
|
||||
stx _SMCDesignator+2
|
||||
.elseif .match ({register}, y)
|
||||
sty _SMCDesignator+2
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
|
||||
.macro SMC_TransferAddressSingle label, address, register
|
||||
.if .paramcount = 2 .or .match ((register), a)
|
||||
.if (.match (.left (1, {adress}), #))
|
||||
; immediate mode
|
||||
lda #<(.right (.tcount ({adress})-1, {adress}))
|
||||
sta _SMCDesignator+1
|
||||
lda #>(.right (.tcount ({adress})-1, {adress}))
|
||||
sta _SMCDesignator+2
|
||||
.else
|
||||
; assume absolute or zero page
|
||||
lda address
|
||||
sta _SMCDesignator+1
|
||||
lda 1+(address)
|
||||
sta _SMCDesignator+2
|
||||
.endif
|
||||
.elseif .match ((register), x)
|
||||
.if (.match (.left (1, {adress}), #))
|
||||
; immediate mode
|
||||
ldx #<(.right (.tcount ({adress})-1, {adress}))
|
||||
stx _SMCDesignator+1
|
||||
ldx #>(.right (.tcount ({adress})-1, {adress}))
|
||||
stx _SMCDesignator+2
|
||||
.else
|
||||
; assume absolute or zero page
|
||||
ldx address
|
||||
stx _SMCDesignator+1
|
||||
ldx 1+(address)
|
||||
stx _SMCDesignator+2
|
||||
.endif
|
||||
.elseif .match ((register), y)
|
||||
.if (.match (.left (1, {adress}), #))
|
||||
; immediate mode
|
||||
ldy #<(.right (.tcount ({adress})-1, {adress}))
|
||||
sty _SMCDesignator+1
|
||||
ldy #>(.right (.tcount ({adress})-1, {adress}))
|
||||
sty _SMCDesignator+2
|
||||
.else
|
||||
; assume absolute or zero page
|
||||
ldy address
|
||||
sty _SMCDesignator+1
|
||||
ldy 1+(address)
|
||||
sty _SMCDesignator+2
|
||||
.endif
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
|
||||
.macro SMC_TransferAddress label, address
|
||||
.if (.match (.left (1, {adress}), #))
|
||||
; immediate mode
|
||||
lda #<(.right (.tcount ({adress})-1, {adress}))
|
||||
sta _SMCDesignator+1
|
||||
ldx #>(.right (.tcount ({adress})-1, {adress}))
|
||||
stx _SMCDesignator+2
|
||||
.else
|
||||
; assume absolute or zero page
|
||||
lda {address}
|
||||
sta _SMCDesignator+1
|
||||
ldx 1+{address}
|
||||
stx _SMCDesignator)+2
|
||||
.endif
|
||||
.endmacro
|
||||
|
||||
.macro SMC_StoreAddress label
|
||||
sta _SMCDesignator+1
|
||||
stx _SMCDesignator+2
|
||||
.endmacro
|
||||
|
||||
|
||||
@ -49,6 +49,7 @@ SGML = apple2.sgml \
|
||||
od65.sgml \
|
||||
pet.sgml \
|
||||
plus4.sgml \
|
||||
smc.sgml \
|
||||
supervision.sgml\
|
||||
vic20.sgml
|
||||
|
||||
|
||||
@ -94,6 +94,10 @@ Main documentation page, contains links to other available stuff.
|
||||
<tag><htmlurl url="library.html" name="library.html"></tag>
|
||||
An overview over the cc65 runtime and C libraries.
|
||||
|
||||
<tag><htmlurl url="smc.html" name="smc.html"></tag>
|
||||
Describes Christian Krügers macro package for writing self modifying
|
||||
assembler code.
|
||||
|
||||
<tag><url name="6502 Binary Relocation Format document"
|
||||
url="http://www.6502.org/users/andre/o65/fileformat.html"></tag>
|
||||
Describes the o65 file format that is used for dynamically loadable modules
|
||||
|
||||
596
doc/smc.sgml
Normal file
596
doc/smc.sgml
Normal file
@ -0,0 +1,596 @@
|
||||
<!doctype linuxdoc system>
|
||||
|
||||
<article>
|
||||
<title>ca65 Macros for Self Modifying Code
|
||||
<author>Christian Krüger
|
||||
<date>2012-02-19
|
||||
|
||||
<abstract>
|
||||
The 'smc.mac' macro package for ca65 eases the use, increases the safeness and
|
||||
self-explanation of 'self-modifying-code' (SMC).
|
||||
</abstract>
|
||||
|
||||
<!-- Table of contents -->
|
||||
<toc>
|
||||
|
||||
<!-- Begin the document -->
|
||||
|
||||
<sect>Overview<p>
|
||||
When reading assembler sources, self modifying code is often hard to identify
|
||||
and applying it needs a lot of discipline.
|
||||
|
||||
Since the cacheless 6502 is a thankful target of such kind of code, the macro
|
||||
package will not only reduce this complexness, but also document the use. The
|
||||
resulting source is more self-explanatory and so easier to maintain.
|
||||
|
||||
While for general purposes SMC is not a desired form for implementations, it
|
||||
can be quite useful for a small range of scenarios. Normally SMC will be
|
||||
introduced when optimizing code in respect to:
|
||||
|
||||
<itemize>
|
||||
<item>speed and/or
|
||||
<item>size.
|
||||
</itemize>
|
||||
|
||||
Please mind that SMC can only be applied for code in RAM, which means that a
|
||||
general purpose library with SMC excludes ROM targets!
|
||||
|
||||
The ca65 SMC macro package consists of two files:
|
||||
|
||||
<itemize>
|
||||
<item><tt>smc.mac</tt>
|
||||
<item><tt>opcodes.inc</tt>
|
||||
</itemize>
|
||||
|
||||
The latter is only needed if you also plan to modify opcodes and not only data
|
||||
within your code.
|
||||
|
||||
<sect>Usage<p>
|
||||
The use of the macros is quite simple:
|
||||
|
||||
Original:
|
||||
|
||||
<tscreen><verb>
|
||||
PHA
|
||||
JSR SUBROUTINE
|
||||
PLA
|
||||
</verb></tscreen>
|
||||
|
||||
By applying SMC, the speed will now be increased by once cycle:
|
||||
|
||||
SMC:
|
||||
|
||||
<tscreen><verb>
|
||||
SMC_StoreValue RestoreAccu
|
||||
JSR SUBROUTINE
|
||||
SMC RestoreAccu, { LDA #SMC_Value }
|
||||
</verb></tscreen>
|
||||
|
||||
The first line stores the value of the accu into the '<tt>RestoreAccu</tt>'
|
||||
labeled SMC target.
|
||||
|
||||
Please note:
|
||||
<enum>
|
||||
<item> for all SMC store or transfer operations, a second argument can be
|
||||
given. This determines the register for the operation:
|
||||
'<tt>SMC_StoreValue Label, y</tt>' will store the value of the
|
||||
Y-register.
|
||||
|
||||
If the second argument is missing, the accu will be used automatically.
|
||||
|
||||
<item> The label targets a 'special SMC namespace'. It fits only to
|
||||
destinations which are introduced with the macro '<tt>SMC</tt>'. A
|
||||
normal label '<tt>RestoreAccu</tt>' wouldn't match and could even
|
||||
coexist (even if you should abstain from doing so).
|
||||
|
||||
<item> The macro '<tt>SMC_StoreValue</tt>' takes care, that the store
|
||||
operation will occur on the value-position of a SMC-instruction. As
|
||||
you will see, other macros influence other instruction part positions.
|
||||
There is no consistency check, if the targeted SMC instruction acually
|
||||
contains a value. Storing a 'value' on an immplied SMC instruction
|
||||
would corrupt the following memory cell!
|
||||
</enum>
|
||||
|
||||
The second line needs no further explanation, this is just a placeholder for
|
||||
some code in the example.
|
||||
|
||||
The third line is the code line which is about to be modified. It has to start
|
||||
with the '<tt>SMC</tt>' macro and must be labeled, so that the modification
|
||||
can be designated. Then the unmodified code is given in curly braces.
|
||||
|
||||
Please note the usage of the value placeholder 'SMC_Value'. Using such a
|
||||
placeholder has two advantages:
|
||||
|
||||
<enum>
|
||||
<item> The code is better documented. It is clearly visible that the given
|
||||
value is about to be changed.
|
||||
<item> When examining an (initial) disassembly (e.g. in a debugger), these
|
||||
placegolders can be better identified: They are fixed and, you may
|
||||
notice that below, quite eye catching defined.
|
||||
</enum>
|
||||
|
||||
<sect1>Argument placeholders<p>
|
||||
|
||||
There are four kinds of placeholders:
|
||||
|
||||
<descrip>
|
||||
|
||||
<label id="Address placeholder">
|
||||
<tag><tt>SMC_AbsAdr</tt></tag>
|
||||
|
||||
Used to indicate an address. The value is '<tt>$FADE</tt>'.
|
||||
|
||||
Example: <tt>STA SMC_AbsAdr</tt>
|
||||
|
||||
|
||||
<label id="Zero-Page-Address placeholder">
|
||||
<tag><tt>SMC_ZpAdr</tt></tag>
|
||||
|
||||
Used to indicate a zero-page-address. The value is '<tt>$00</tt>'.
|
||||
|
||||
Example: <tt>LDA SMC_ZpAdr</tt>
|
||||
|
||||
|
||||
<label id="Opcode placeholder">
|
||||
<tag><tt>SMC_Opcode</tt></tag>
|
||||
|
||||
Used to indicate an instruction. The value is '<tt>NOP</tt>'.
|
||||
|
||||
Example: <tt>SMC_Opcode</tt>
|
||||
|
||||
|
||||
<label id="Immediate value placeholder">
|
||||
<tag><tt>SMC_Value</tt></tag>
|
||||
|
||||
Used to indicate a value. The value is '<tt>$42</tt>'.
|
||||
|
||||
Example: <tt>LDX #SMC_Value</tt>
|
||||
</descrip>
|
||||
|
||||
Attention: Often code is modified after the initial use - where using the
|
||||
placeholders does not makes sense. Please mind also, that in very variable
|
||||
expressions (e.g. opcode and argument is about to be changed), placeholders
|
||||
can lead to unidentifyable code for a debugger/disassembler:
|
||||
|
||||
<tt>SMC Example, { SMC_Opcode SMC_AbsAdr } </tt>
|
||||
|
||||
Since the opcode is '<tt/NOP/', the value '<tt/$DE/' from '<tt/$FADE/' will
|
||||
interpreted as opcode in a disassembler too. This breaks the correct
|
||||
disassembly, because '<tt/$DE/' is interpreted as '<tt/DEC abx/'. Establishing
|
||||
a valid placeholder instruction may be better:
|
||||
|
||||
<tt>SMC Example, { sta SMC_AbsAdr } ; Note: Opcode will be modified too!</tt>
|
||||
|
||||
<sect1>Accessing opcodes<p>
|
||||
|
||||
Some macros are designed to access the instruction of a code line. To increase
|
||||
readability, please use the opcodes as defined in the '<tt>opcodes.inc</tt>'
|
||||
file.
|
||||
|
||||
<descrip>
|
||||
|
||||
<label id="Transfer opcode">
|
||||
<tag><tt>SMC_TransferOpcode label, opcode (, register)</tt></tag>
|
||||
Loads and store an opcode to given SMC instruction.
|
||||
|
||||
Example:
|
||||
|
||||
<tscreen><verb>
|
||||
SMC SumRegister, { LDA #10 }
|
||||
JSR OUTPUT
|
||||
SMC_TransferOpcode SumRegister, OPC_ADC_imm, x
|
||||
</verb></tscreen>
|
||||
|
||||
The macro above will load the opcode '<tt>ADC #</tt>' into the x - register
|
||||
and stores it at the place of the '<tt>LDA #</tt>'.
|
||||
|
||||
<label id="Load opcode">
|
||||
<tag><tt>SMC_LoadOpcode label (, register)</tt></tag>
|
||||
Loads the opcode of a SMC line to the given register.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC ShiftOrNothing, { LSL }
|
||||
SMC_LoadOpcode ShiftOrNothing, y
|
||||
CPY #OPC_NOP
|
||||
BEQ Exit
|
||||
</verb></tscreen>
|
||||
|
||||
<label id="Store opcode">
|
||||
<tag><tt>SMC_StoreOpcode label (, register)</tt></tag>
|
||||
Stores the value of the given register at the opcode place of a SMC line.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SetBoldMode:
|
||||
LDA #OPC_INX
|
||||
SMC_StoreOpcode AdaptCharWidth
|
||||
SMC_StoreOpcode AdaptUnderlineWidth
|
||||
RTS
|
||||
...
|
||||
SMC AdaptCharWidth, { NOP }
|
||||
...
|
||||
SMC AdaptUnderlineWidth, { NOP }
|
||||
</verb></tscreen>
|
||||
|
||||
</descrip>
|
||||
|
||||
<sect1>Accessing arguments<p>
|
||||
|
||||
These marcos are determined to get, set and change arguments of instructions:
|
||||
|
||||
<descrip>
|
||||
|
||||
<label id="Change branch">
|
||||
<tag><tt>SMC_ChangeBranch label, destination (, register)</tt></tag>
|
||||
|
||||
Used to modify the destination of a branch instruction. If the adress offset
|
||||
exceeds the supported range of 8-bit of the 6502, a error will be thrown.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
Disable Handler:
|
||||
SMC_ChangeBranch BranchToHandler, Exit
|
||||
RTS
|
||||
...
|
||||
LDA warning
|
||||
SMC BranchToHandler, { BNE Handler }
|
||||
Exit:
|
||||
RTS
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Transfer value">
|
||||
<tag><tt>SMC_TransferValue label, value (, register)</tt></tag>
|
||||
|
||||
Changes the value of a SMC line.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
ClearDefault:
|
||||
SMC_TransferValue LoadDefault, 0
|
||||
RTS
|
||||
...
|
||||
SMC LoadDefault, { LDX #25 }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Load value">
|
||||
<tag><tt>SMC_LoadValue label (, register)</tt></tag>
|
||||
|
||||
Retreives the value of a SMC line.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
ShowDefault:
|
||||
SMC_LoadValue LoadDefault
|
||||
JSR PrintValue
|
||||
RTS
|
||||
...
|
||||
SMC LoadDefault, { LDX #25 }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Store value">
|
||||
<tag><tt>SMC_StoreValue label (, register)</tt></tag>
|
||||
|
||||
Stores the value in the register to given SMC line.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
InitCounters:
|
||||
LDY #0
|
||||
SMC_StoreValue GetI, y
|
||||
SMC_StoreValue GetJ, y
|
||||
SMC_StoreValue GetK, y
|
||||
...
|
||||
SMC GetI, { LDX #SMC_Value }
|
||||
...
|
||||
SMC GetJ, { LDX #SMC_Value }
|
||||
...
|
||||
SMC GetK, { LDX #SMC_Value }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Transfer low-byte">
|
||||
<tag><tt>SMC_TransferLowByte label, value (, register)</tt></tag>
|
||||
|
||||
Does the same as '<tt>SMC_TransferValue</tt>' but should be used for
|
||||
low-bytes of adresses for better readability.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
ActivateSecondDataSet:
|
||||
SMC_TransferLowByte LoadData, $40
|
||||
RTS
|
||||
...
|
||||
SMC LoadData, { LDA $2000 }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Load low-byte">
|
||||
<tag><tt>SMC_LoadLowByte label (, register)</tt></tag>
|
||||
|
||||
Does the same as '<tt>SMC_LoadValue</tt>' but should be used for low-bytes
|
||||
of adresses for better readability.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
IsSecondDataSetActive:
|
||||
SMC_LoadLowByte LoadData, y
|
||||
CPY #$40
|
||||
BNE NotActive
|
||||
...
|
||||
SMC LoadData, { LDA $2000 }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Store low-byte">
|
||||
<tag><tt>SMC_StoreLowByte label (, register)</tt></tag>
|
||||
|
||||
Does the same as '<tt>SMC_StoreValue</tt>' but should be used for low-bytes
|
||||
of adresses for better readability.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
InitStructureBaseAddresses:
|
||||
LDX #0
|
||||
SMC_StoreLowByte GetPlayerGraphic, x
|
||||
SMC_StoreLowByte GetObjectGraphic, x
|
||||
SMC_StoreLowByte StoreCollisionData, x
|
||||
RTS
|
||||
...
|
||||
SMC GetPlayerGraphic, { LDX $2000 }
|
||||
...
|
||||
SMC GetObjectGraphic, { LDA $2100,x }
|
||||
...
|
||||
SMC StoreCollisionData, { STY $2200 }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Transfer high-byte">
|
||||
<tag><tt>SMC_TransferHighByte label, value (, register)</tt></tag>
|
||||
|
||||
Loads and stores the given value via the named register to the high-byte
|
||||
adress portion of an SMC-instruction.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
PlaySFX:
|
||||
SMC GetVolume { LDA $3200,x }
|
||||
STA SoundOut
|
||||
INX
|
||||
BNE PlaySFX
|
||||
...
|
||||
PlayOtherSound:
|
||||
SMC_TransferHighByte GetVolume, $34
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Load high-byte">
|
||||
<tag><tt>SMC_LoadHighByte label (, register)</tt></tag>
|
||||
|
||||
Loads the high-byte part of an SMC-instruction adress to the given register.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
PlaySFX:
|
||||
SMC GetVolume { LDA $3200,x }
|
||||
...
|
||||
SMC_LoadHighByte GetVolume
|
||||
cmp #$34
|
||||
beq OtherSoundPlaying
|
||||
...
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Store high-byte">
|
||||
<tag><tt>SMC_StoreHighByte label (, register)</tt></tag>
|
||||
|
||||
Stores the high-byte adress part of an SMC-instruction from the given
|
||||
register.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SetupLevel2:
|
||||
LDX #(>Level2Base)
|
||||
SMC_StoreHighByte GetLevelData, x
|
||||
SMC_StoreHighByte GetScreenData, x
|
||||
SMC_StoreHighByte GetSoundData, x
|
||||
RTS
|
||||
...
|
||||
SMC GetLevelData, { LDA Level1Base+Data }
|
||||
...
|
||||
SMC GetScreenData, { LDA Level1Base+Screen, x }
|
||||
...
|
||||
SMC GetSoundData, { LDA Level1Base+Sound, y }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Transfer single adress">
|
||||
<tag><tt>SMC_TransferAddressSingle label, address (, register)</tt></tag>
|
||||
|
||||
Transfers the contents of the given address via the given register to the
|
||||
designated SMC instruction.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
PrintHello:
|
||||
SMC_TransferAddressSingle GetChar, #HelloMsg
|
||||
...
|
||||
LDX #0
|
||||
NextChar:
|
||||
SMC GetChar, { LDA SMC_AbsAdr, x }
|
||||
BEQ leave
|
||||
JSR CharOut
|
||||
INX
|
||||
BNE NextChar
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Transfer adress">
|
||||
<tag><tt>SMC_TransferAddress label, address</tt></tag>
|
||||
|
||||
Loads contents of given address to A/X and stores the result to SMC
|
||||
instruction. Allows reuse of register contents by using
|
||||
'<tt>SMC_StoreAddress</tt>' for multiple SMC instruction modifications.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC_TransferAddress JumpTo, #CloseChannel, Y
|
||||
...
|
||||
SMC JumpTo, { JMP OpenChannel }
|
||||
</verb></tscreen>
|
||||
|
||||
|
||||
<label id="Store address">
|
||||
<tag><tt>SMC_StoreAddress label</tt></tag>
|
||||
|
||||
Stores the address value in a/x to a SMC instruction address position.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC_StoreAddress GetData
|
||||
...
|
||||
SMC GetData, { LDA SMC_AbsAdr }
|
||||
</verb></tscreen>
|
||||
|
||||
</descrip>
|
||||
|
||||
<sect1>Operational macros<p>
|
||||
|
||||
These marcos are determined to let read/modify/write opcodes work on parts of
|
||||
SMC instructions.
|
||||
|
||||
<descrip>
|
||||
|
||||
<label id="Operate on value">
|
||||
<tag><tt>SMC_OperateOnValue opcode, label</tt></tag>
|
||||
|
||||
Let given opcode work on the value part of a SMC instruction.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC_OperateOnValue ASL, LoadMask ; shift mask to left
|
||||
...
|
||||
SMC LoadMask, { LDA #$20 }
|
||||
</verb></tscreen>
|
||||
|
||||
<label id="Operate on low-byte">
|
||||
<tag><tt>SMC_OperateOnLowByte opcode, label</tt></tag>
|
||||
|
||||
Same as '<tt/SMC_OperateOnValue/' but renamed for better readability when
|
||||
accessing low-bytes of address.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC_OperateOnLowByte DEC, AccessData
|
||||
...
|
||||
SMC AccessData, { LDX Data }
|
||||
</verb></tscreen>
|
||||
|
||||
<label id="Operate on high-byte">
|
||||
<tag><tt>SMC_OperateOnHighByte opcode, label</tt></tag>
|
||||
|
||||
Let the given opcode work on the high-byte part on a SMC-instruction.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
NextPage:
|
||||
SMC_OperateOnHighByte INC, GetPageData
|
||||
...
|
||||
SMC GetPageData, { LDA SourceData, X }
|
||||
</verb></tscreen>
|
||||
</descrip>
|
||||
|
||||
<sect1>Scope macros<p>
|
||||
|
||||
These marcos are determined to export and import SMC labels out of the current
|
||||
file scope. Please handle with care! If you cannot abstain from leaving the
|
||||
file scope, you should at least document the exported SMC lines very well. On
|
||||
import side no checking is available if the SMC line is correct accessed (e.g.
|
||||
invalid access to the value of an implied instruction)!
|
||||
|
||||
<descrip>
|
||||
<label id="Export SMC line under given name">
|
||||
<tag><tt>SMC_Export alias, label</tt></tag>
|
||||
|
||||
SMC label will be exported under given alias.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
.proc GetValue
|
||||
SMC LoadValue, { LDA #12 }
|
||||
rts
|
||||
.endproc
|
||||
|
||||
SMC_Export GetValueLoader, GetValue::LoadValue
|
||||
</verb></tscreen>
|
||||
|
||||
<label id="Import SMC alias">
|
||||
<tag><tt>SMC_Import alias</tt></tag>
|
||||
|
||||
SMC line is made accessible under given alias.
|
||||
|
||||
Example:
|
||||
<tscreen><verb>
|
||||
SMC_Import GetValueLoader
|
||||
...
|
||||
SMC_TransferValue GetValueLoader, #47
|
||||
...
|
||||
</verb></tscreen>
|
||||
</descrip>
|
||||
|
||||
<sect>A complex example<p>
|
||||
Let's have a look on a quite sophisticated example for the usage of SMC. It
|
||||
not only modifies code, but also the modification of the code is modified -
|
||||
allowing reuse of some instructions.
|
||||
|
||||
The code is from my 'memset()'implementation:
|
||||
|
||||
<descrip>
|
||||
<tscreen><verb>
|
||||
1: ...
|
||||
2: SMC_StoreAddress StoreAccuFirstSection
|
||||
3:
|
||||
4: StoreToFirstSection:
|
||||
5: SMC StoreAccuFirstSection, { sta SMC_AbsAdr, Y }
|
||||
6: ...
|
||||
7: RestoreCodeBranchBaseAdr:
|
||||
8: SMC FirstIncHighByte, { SMC_OperateOnHighByte inc, StoreAccuFirstSection } ; code will be overwritten to 'beq RestoreCode' (*)
|
||||
9: ...
|
||||
10: SMC_TransferOpcode FirstIncHighByte, OPC_BEQ , x ; change code marked above with (*)
|
||||
11: SMC_TransferValue FirstIncHighByte, #(restoreCode - RestoreCodeBranchBaseAdr-2), x ; set relative adress to 'RestoreCode'
|
||||
12: ...
|
||||
13: restoreCode:
|
||||
14: SMC_TransferOpcode FirstIncHighByte, OPC_INC_abs , x ; restore original code...
|
||||
15: SMC_TransferValue FirstIncHighByte, #(<(StoreToFirstSection+2)), x ; (second byte of inc contained low-byte of adress)
|
||||
16: ...
|
||||
</verb></tscreen>
|
||||
|
||||
Some explanation:
|
||||
|
||||
Line 2: The register pair A/X contains an address, which is stored on the
|
||||
address location of a SMC line called 'StoreAccuFirstSection'. According to
|
||||
cc65's calling convention, the low-byte is in accu while the high-byte is in
|
||||
the X-register.
|
||||
|
||||
Line 5: The (modified) address is accessed.
|
||||
|
||||
Line 8: We have a line here, which is about to be modified (it begins with
|
||||
SMC), but itself modifies code. Please note: Contrary to the rest of SMC-line
|
||||
modifying macros, the 'OperateOn'-macros just expand their given arguments
|
||||
into a single instruction line. These can be changed of course too.
|
||||
|
||||
Line 10,11: These lines construct a branch operation for line 8: The
|
||||
X-register will be used to change it from 'inc StoreAccuFirstSection+2'
|
||||
(high-byte operation) to 'beq restoreCode'. Please note: To calculate the
|
||||
relaive branch offset, we introduced a second label
|
||||
('RestoreCodeBranchBaseAdr') for to calculate it. Some could also use the
|
||||
internal name of the SMC label, but you should abstain to do so - it may be
|
||||
changed in the future...
|
||||
|
||||
Line 14,15: The original code from line 8 is reestablished.
|
||||
</descrip>
|
||||
</article>
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user