95 lines
3.4 KiB
Ruby
95 lines
3.4 KiB
Ruby
require_relative "instruction"
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module Arm
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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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module LogicHelper
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# ADDRESSING MODE 1
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# Logic ,Maths, Move and compare instructions (last three below)
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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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#(stays in subclases, while build is overriden to provide different arguments)
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def do_build(arg)
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if arg.is_a?(Vm::StringLiteral)
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# do pc relative addressing with the difference to the instuction
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# 8 is for the funny pipeline adjustment (ie oc pointing to fetch and not execute)
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arg = Arm::NumLiteral.new( arg.position - self.position - 8 )
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@rn = :pc
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end
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if( arg.is_a? Fixnum ) #HACK to not have to change the code just now
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arg = Arm::NumLiteral.new( arg )
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end
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if( arg.is_a? Vm::Signed ) #HACK to not have to change the code just now
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arg = Arm::NumLiteral.new( arg.value )
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end
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if (arg.is_a?(Arm::NumLiteral))
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if (arg.value.fits_u8?)
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# no shifting needed
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@operand = arg.value
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@i = 1
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elsif (op_with_rot = calculate_u8_with_rr(arg))
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@operand = op_with_rot
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@i = 1
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else
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raise "cannot fit numeric literal argument in operand #{arg.inspect}"
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end
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elsif (arg.is_a?(Symbol))
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@operand = arg
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@i = 0
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elsif (arg.is_a?(Arm::Shift))
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rm_ref = arg.argument
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@i = 0
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shift_op = {'lsl' => 0b000, 'lsr' => 0b010, 'asr' => 0b100,
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'ror' => 0b110, 'rrx' => 0b110}[arg.type]
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if (arg.type == 'ror' and arg.value.nil?)
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# ror #0 == rrx
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raise "cannot rotate by zero #{arg} #{inspect}"
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end
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arg1 = arg.value
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if (arg1.is_a?(Arm::NumLiteral))
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if (arg1.value >= 32)
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raise "cannot shift by more than 31 #{arg1} #{inspect}"
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end
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shift_imm = arg1.value
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elsif (arg1.is_a?(Arm::Register))
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shift_op val |= 0x1;
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shift_imm = arg1.number << 1
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elsif (arg.type == 'rrx')
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shift_imm = 0
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end
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@operand = rm_ref | (shift_op << 4) | (shift_imm << 4+3)
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else
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raise "invalid operand argument #{arg.inspect} , #{inspect}"
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end
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end
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def assemble(io)
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build
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instuction_class = 0b00 # OPC_DATA_PROCESSING
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val = @operand.is_a?(Symbol) ? reg_code(@operand) : @operand
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raise inspect unless reg_code(@rd)
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val |= (reg_code(@rd) << 12)
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val |= (reg_code(@rn) << 12+4)
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val |= (@update_status_flag << 12+4+4)#20
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val |= (op_bit_code << 12+4+4 +1)
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val |= (@i << 12+4+4 +1+4)
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val |= (instuction_class << 12+4+4 +1+4+1)
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val |= (cond_bit_code << 12+4+4 +1+4+1+2)
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io.write_uint32 val
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end
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end
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end |