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273 lines
8.7 KiB
Ruby
273 lines
8.7 KiB
Ruby
# frozen_string_literal: true
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require_relative 'opcodes'
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require_relative 'regexes'
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module N65
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# Represents a single 6502 Instruction
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class Instruction
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attr_reader :op, :arg, :mode, :hex, :description, :length, :cycles, :boundry_add, :flags, :address
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# Custom Exceptions
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class InvalidInstruction < StandardError; end
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class UnresolvedSymbols < StandardError; end
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class InvalidAddressingMode < StandardError; end
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class AddressOutOfRange < StandardError; end
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class ArgumentTooLarge < StandardError; end
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# Include Regexes
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include Regexes
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ADDRESSING_MODES = {
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relative: {
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example: 'B** my_label',
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display: '%s $%.4X',
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regex: /$^/i,
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regex_label: /^#{Branches}\s+#{Sym}$/
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},
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immediate: {
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example: 'AAA #$FF',
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display: '%s #$%.2X',
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regex: /^#{Mnemonic}\s+#{Immediate}$/,
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regex_label: /^#{Mnemonic}\s+#(<|>)#{Sym}$/
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},
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implied: {
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example: 'AAA',
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display: '%s',
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regex: /^#{Mnemonic}$/
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},
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zero_page: {
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example: 'AAA $FF',
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display: '%s $%.2X',
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regex: /^#{Mnemonic}\s+#{Num8}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}\s+zp$/
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},
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zero_page_x: {
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example: 'AAA $FF, X',
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display: '%s $%.2X, X',
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regex: /^#{Mnemonic}\s+#{Num8}\s?,\s?#{XReg}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{XReg}\s+zp$/
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},
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zero_page_y: {
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example: 'AAA $FF, Y',
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display: '%s $%.2X, Y',
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regex: /^#{Mnemonic}\s+#{Num8}\s?,\s?#{YReg}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{YReg}\s+zp$/
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},
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absolute: {
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example: 'AAA $FFFF',
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display: '%s $%.4X',
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regex: /^#{Mnemonic}\s+#{Num16}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}$/
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},
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absolute_x: {
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example: 'AAA $FFFF, X',
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display: '%s $%.4X, X',
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regex: /^#{Mnemonic}\s+#{Num16}\s?,\s?#{XReg}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{XReg}$/
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},
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absolute_y: {
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example: 'AAA $FFFF, Y',
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display: '%s $%.4X, Y',
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regex: /^#{Mnemonic}\s+#{Num16}\s?,\s?#{YReg}$/,
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regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{YReg}$/
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},
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indirect: {
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example: 'AAA ($FFFF)',
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display: '%s ($%.4X)',
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regex: /^#{Mnemonic}\s+\(#{Num16}\)$/,
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regex_label: /^#{Mnemonic}\s+\(#{Sym}\)$/
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},
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indirect_x: {
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example: 'AAA ($FF, X)',
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display: '%s ($%.2X, X)',
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regex: /^#{Mnemonic}\s+\(#{Num8}\s?,\s?#{XReg}\)$/,
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regex_label: /^#{Mnemonic}\s+\(#{Sym}\s?,\s?#{XReg}\)$/
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},
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indirect_y: {
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example: 'AAA ($FF), Y)',
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display: '%s ($%.2X), Y',
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regex: /^#{Mnemonic}\s+\(#{Num8}\)\s?,\s?#{YReg}$/,
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regex_label: /^#{Mnemonic}\s+\(#{Sym}\)\s?,\s?#{YReg}$/
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}
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}.freeze
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# Parse one line of assembly, returns nil if the line
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# is ultimately empty of asm instructions
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# Raises SyntaxError if the line is malformed in some way
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def self.parse(line)
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# Try to parse this line in each addressing mode
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ADDRESSING_MODES.each do |mode, parse_info|
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# We have regexes that match each addressing mode
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match_data = parse_info[:regex].match(line)
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unless match_data.nil?
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# We must have a straight instruction without symbols, construct
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# an Instruction from the match_data, and return it
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_, op, arg_hex, arg_bin = match_data.to_a
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# Until I think of something better, it seems that the union regex
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# puts a hexidecimal argument in one capture, and a binary in the next
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# This is annoying, but still not as annoying as using Treetop to parse
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if !arg_hex.nil?
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return Instruction.new(op, arg_hex.to_i(16), mode)
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elsif !arg_bin.nil?
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return Instruction.new(op, arg_bin.to_i(2), mode)
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else
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return Instruction.new(op, nil, mode)
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end
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else
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# Can this addressing mode even use labels?
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unless parse_info[:regex_label].nil?
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# See if it does in fact have a symbolic argument
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match_data = parse_info[:regex_label].match(line)
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unless match_data.nil?
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# We have found an assembly instruction containing a symbolic
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# argument. We can resolve this symbol later by looking at the
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# symbol table in the #exec method
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match_array = match_data.to_a
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# If we have a 4 element array, this means we matched something
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# like LDA #<label, which is a legal immediate one byte value
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# by taking the msb. We need to make that distinction in the
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# Instruction, by passing an extra argument
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if match_array.size == 4
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_, op, byte_selector, arg = match_array
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return Instruction.new(op, arg, mode, byte_selector.to_sym)
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else
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_, op, arg = match_array
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return Instruction.new(op, arg, mode)
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end
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end
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end
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end
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end
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# We just don't recognize this line of asm, it must be a Syntax Error
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raise(SyntaxError, line)
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end
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# Create an instruction. Having the instruction op a downcased symbol is nice
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# because that can later be used to index into our opcodes hash in OpCodes
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# OpCodes contains the definitions of each OpCode
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def initialize(op, arg, mode, byte_selector = nil)
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@byte_selector = byte_selector.nil? ? nil : byte_selector.to_sym
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raise(InvalidInstruction, "Bad Byte selector: #{byte_selector}") unless [:>, :<, nil].include?(@byte_selector)
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## Lookup the definition of this opcode, otherwise it is an invalid instruction
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@op = op.downcase.to_sym
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definition = OpCodes[@op]
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raise(InvalidInstruction, op) if definition.nil?
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@arg = arg
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# Be sure the mode is an actually supported mode.
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@mode = mode.to_sym
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raise(InvalidAddressingMode, mode) unless ADDRESSING_MODES.key?(@mode)
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raise(InvalidInstruction, "#{op} cannot be used in #{mode} mode") if definition[@mode].nil?
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@description, @flags = definition.values_at(:description, :flags)
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@hex, @length, @cycles, @boundry_add = definition[@mode].values_at(:hex, :len, :cycles, :boundry_add)
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end
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# Is this instruction a zero page instruction?
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def zero_page_instruction?
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%i[zero_page zero_page_x zero_page_y].include?(@mode)
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end
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# Execute writes the emitted bytes to virtual memory, and updates PC
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# If there is a symbolic argument, we can try to resolve it now, or
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# promise to resolve it later.
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def exec(assembler)
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promise = assembler.with_saved_state do |saved_assembler|
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@arg = saved_assembler.symbol_table.resolve_symbol(@arg)
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# If the instruction uses a byte selector, we need to apply that.
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@arg = apply_byte_selector(@byte_selector, @arg)
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# If the instruction is relative we need to work out how far away it is
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@arg = @arg - saved_assembler.program_counter - 2 if @mode == :relative
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saved_assembler.write_memory(emit_bytes)
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end
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case @arg
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when Integer, NilClass
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assembler.write_memory(emit_bytes)
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when String
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begin
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# This works correctly now :)
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promise.call
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rescue SymbolTable::UndefinedSymbol
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placeholder = [@hex, 0xDE, 0xAD][0...@length]
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# I still have to write a placeholder instruction of the right
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# length. The promise will come back and resolve the address.
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assembler.write_memory(placeholder)
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promise
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end
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end
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end
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# Apply a byte selector to an argument
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def apply_byte_selector(byte_selector, value)
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return value if byte_selector.nil?
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case byte_selector
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when :>
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high_byte(value)
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when :<
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low_byte(value)
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end
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end
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# Emit bytes from asm structure
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def emit_bytes
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case @length
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when 1
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[@hex]
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when 2
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if zero_page_instruction? && @arg.netagive? || @arg > 0xff
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raise(ArgumentTooLarge, "For #{@op} in #{@mode} mode, only 8-bit values are allowed")
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end
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[@hex, @arg]
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when 3
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[@hex] + break_16(@arg)
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else
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raise("Can't handle instructions > 3 bytes")
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end
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end
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private
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# Break an integer into two 8-bit parts
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def break_16(integer)
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[integer & 0x00FF, (integer & 0xFF00) >> 8]
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end
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# Take the high byte of a 16-bit integer
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def high_byte(word)
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(word & 0xFF00) >> 8
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end
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# Take the low byte of a 16-bit integer
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def low_byte(word)
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word & 0xFF
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end
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end
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end
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