46 lines
1.6 KiB
Ruby
46 lines
1.6 KiB
Ruby
require_relative "assembly_error"
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require_relative "arm_machine"
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module Asm
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class Code ; end
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# Not surprisingly represents an cpu instruction.
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# This is an abstract base class, with derived classes
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# Logic / Move / Compare / Stack / Memory (see there)
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#
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# Opcode is a (<= three) letter accronym (same as in assembly code). Though in arm, suffixes can
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# make the opcode longer, we chop those off in the constructor
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# Argurments are registers or labels or string/num Literals
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class Instruction < Code
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include ArmMachine
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COND_POSTFIXES = Regexp.union( COND_CODES.keys.collect{|k|k.to_s} ).source
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def initialize(opcode , condition_code , update_status , args)
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@update_status_flag = update_status
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@condition_code = condition_code.to_sym
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@opcode = opcode
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@args = args
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@operand = 0
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end
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attr_reader :opcode, :args
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# Many arm instructions may be conditional, where the default condition is always (al)
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# ArmMachine::COND_CODES names them, and this attribute reflects it
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attr_reader :condition_code
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attr_reader :operand
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# Logic instructions may be executed with or without affecting the status register
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# Only when an instruction affects the status is a subsequent compare instruction effective
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# But to make the conditional execution (see cond) work for more than one instruction, one needs to
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# be able to execute without changing the status
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attr_reader :update_status_flag
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# arm intrucioons are pretty sensible, and always 4 bytes (thumb not supported)
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def length
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4
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end
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end
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end |