90 lines
2.7 KiB
Markdown
90 lines
2.7 KiB
Markdown
# 6502-emu
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A relatively bug-free and simple 6502 emulator. It is capable of running ehBasic.
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Many 6502 emulators make extensive use of macros, which I personally think makes
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code harder to understand. At the other extreme, some emulators implement each
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addressing mode of each instruction separately, which is a big waste of time and
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makes the code harder to maintain.
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I chose a middle-ground, and used lookup tables for instruction decoding and address
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decoding. This also gets rid of the common "giant opcode switch statement" (which
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can be seen in my CHIP8 emulator project).
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### Usage Example:
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```
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[david@D-ARCH 6502-emu]$ ./6502-emu examples/ehbasic.rom
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Enhanced 6502 BASIC 2.22 (c) Lee Davison
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[C]old/[W]arm ?
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Memory size ?
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40191 Bytes free
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Enhanced BASIC 2.22
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Ready
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10 X1=59
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15 Y1=21
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20 I1=-1.0
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23 I2=1.0
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26 R1=-2.0
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28 R2=1.0
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30 S1=(R2-R1)/X1
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35 S2=(I2-I1)/Y1
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40 FOR Y=0 TO Y1
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50 I3=I1+S2*Y
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60 FOR X=0 TO X1
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70 R3=R1+S1*X
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73 Z1=R3
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76 Z2=I3
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80 FOR N=0 TO 30
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90 A=Z1*Z1
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95 B=Z2*Z2
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100 IF A+B>4.0 GOTO 130
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110 Z2=2*Z1*Z2+I3
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115 Z1=A-B+R3
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120 NEXT N
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130 PRINT CHR$(63-N);
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140 NEXT X
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150 PRINT
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160 NEXT Y
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170 END
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RUN
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??????>>>>>===============<<<<<<;;;:7143;<<<<====>>>>>>>>>>>
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?????>>>================<<<<<<<;;;984+18:;;<<<<=====>>>>>>>>
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????>>>===============<<<<<<<;;::85 )/:;;;;<<=====>>>>>>>
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???>>===============<<<<<<;:9999875 689::::;<<=====>>>>>
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??>>=============<<<<;;;;::7/ '3 56446;<======>>>>
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??>===========<<<;;;;;;:::863 +8:;<======>>>
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?>========<<<;6::::::::997! &89;<<======>>
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?====<<<<<;;;:83567.678874 ,:<<=======>
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?=<<<<<<;;;;:986' /4 +:<<<======>
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?<<<<<<;;::8675( ( 9;<<<======>
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?;;:999:88460 '9:;<<<======>
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?;;:999:88460 '9:;<<<======>
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?<<<<<<;;::8675( ( 9;<<<======>
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?=<<<<<<;;;;:986' /4 +:<<<======>
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?====<<<<<;;;:83567.678874 ,:<<=======>
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?>========<<<;6::::::::997! &89;<<======>>
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??>===========<<<;;;;;;:::863 +8:;<======>>>
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??>>=============<<<<;;;;::7/ '3 56446;<======>>>>
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???>>===============<<<<<<;:9999875 689::::;<<=====>>>>>
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????>>>===============<<<<<<<;;::85 )/:;;;;<<=====>>>>>>>
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?????>>>================<<<<<<<;;;984+18:;;<<<<=====>>>>>>>>
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??????>>>>>===============<<<<<<;;;:7143;<<<<====>>>>>>>>>>>
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Ready
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```
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### TODO:
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- Decimal mode.
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- Cycle-accurate timing.
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- GDB interface for easy debugging of 6502 programs (and the emulator itself).
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- Implement more hardware devices (mainly a 6522, also some character/graphics LCDs).
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- Turn it into a NES emulator.
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