2015-02-18 02:26:26 +00:00
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# assembler6502
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2015-02-18 03:05:37 +00:00
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2015-02-18 11:05:18 +00:00
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An assembler for the 6502 microprocessor written in Ruby
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2015-02-18 03:05:37 +00:00
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6502 Assembler
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Usage: ./assembler\_6502.rb <infile.asm> -o outfile.nes
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This is a pretty straightfoward assembler, that is currently set up
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to produce iNES ROM formatted binaries from simple assembly listings.
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It is good at knowing which addressing modes are and are not allowed for
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each instruction, and contains some examples of correct syntax.
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Parsing is done by Regular Expression, because, well the language is
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so regular, it actually took less time than anything else I've tried
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to parse in the past, including Scheme using parsec.
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It handles labels, and does a two pass assembly, first assembling
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the byte codes, and then going back and filling in the proper addresses
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where labels were used.
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I have used this to compile some code for the NES, and it ran correctly
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on FCEUX, got it to make some sounds, etc.
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Some Todos:
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- I need to add the #\<$800 and #\>$800 style operators to select the
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MSB and LSB of immediate values during assembly.
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- I may make this into a Rubygem
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- Maybe I can put some better error messages.
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- I should just make a 6502 CPU emulator probably now too.
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2015-02-18 12:05:00 +00:00
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Some new additions:
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- added .org directive
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- added .dw directive
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- added .bytes directive
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- added .incbin directive
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- Invented my own iNES header directive that is JSON
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- Split the project up into separate files per class
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- Wrote some more unit tests
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- Added OptionParser for commandline opts
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- Tested a ROM with Sound output
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- Tested a ROM that changes background color
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I decided that during the first pass of assembly, I should just initialize
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an entire 65535 byte virtual memory images, and write the instructions to
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their correct places, and then after resolving symbols during the second pass,
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I just clip out the Cartridge ROM area and iNES header at the end, works great
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so far.
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Next up I will port some more tutorials that use sprites and use controller input
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and sound all together.
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