96 lines
3.2 KiB
Ruby
96 lines
3.2 KiB
Ruby
require_relative "nodes"
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module Arm
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# ADDRESSING MODE 2
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# Implemented: immediate offset with offset=0
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class MemoryInstruction < Vm::MemoryInstruction
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include Arm::Constants
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def initialize(attributes)
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super(attributes)
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@attributes[:update_status_flag] = 0
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@attributes[:condition_code] = :al
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@operand = 0
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@pre_post_index = 0 #P flag
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@add_offset = 0 #U flag
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@is_load = opcode.to_s[0] == "l" ? 1 : 0 #L (load) flag
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@rn = :r0 # register zero = zero bit pattern
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@rd = :r0 # register zero = zero bit pattern
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end
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# attr_accessor :i, :pre_post_index, :add_offset, :byte_access, :w, :is_load, :rn, :rd
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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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# Build representation for target address
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def build
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if( @is_load )
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@rd = @attributes[:left]
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arg = @attributes[:right]
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else #store
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@rd = @attributes[:right]
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arg = @attributes[:left]
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end
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#str / ldr are _serious instructions. With BIG possibilities not half are implemented
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if (arg.is_a?(Symbol)) #symbol is register
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@rn = arg
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if @attributes[:offset]
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@operand = @attributes[:offset]
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if (@operand < 0)
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@add_offset = 0
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#TODO test/check/understand
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@operand *= -1
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else
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@add_offset = 1
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end
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if (@operand.abs > 4095)
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raise "reference offset too large/small (max 4095) #{arg} #{inspect}"
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end
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end
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elsif (arg.is_a?(Vm::StringConstant)) #use pc relative
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@rn = :pc
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@operand = arg.position - self.position - 8 #stringtable is after code
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@add_offset = 1
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if (@operand.abs > 4095)
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raise "reference offset too large/small (max 4095) #{arg} #{inspect}"
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end
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elsif (arg.is_a?(Arm::Label) or arg.is_a?(Arm::NumLiteral))
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@pre_post_index = 1
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@rn = pc
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@use_addrtable_reloc = true
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@addrtable_reloc_target = arg
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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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i = 0 #I flag (third bit)
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#not sure about these 2 constants. They produce the correct output for str r0 , r1
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# but i can't help thinking that that is because they are not used in that instruction and
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# so it doesn't matter. Will see
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@add_offset = 1
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@pre_post_index = 1
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w = 0 #W flag
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byte_access = opcode.to_s[-1] == "b" ? 1 : 0 #B (byte) flag
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instuction_class = 0b01 # OPC_MEMORY_ACCESS
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val = @operand.is_a?(Symbol) ? reg_code(@operand) : @operand
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val |= (reg_code(@rd) << 12 )
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val |= (reg_code(@rn) << 12+4) #16
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val |= (@is_load << 12+4 +4)
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val |= (w << 12+4 +4+1)
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val |= (byte_access << 12+4 +4+1+1)
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val |= (@add_offset << 12+4 +4+1+1+1)
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val |= (@pre_post_index << 12+4 +4+1+1+1+1)#24
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val |= (i << 12+4 +4+1+1+1+1 +1)
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val |= (instuction_class<<12+4 +4+1+1+1+1 +1+1)
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val |= (cond_bit_code << 12+4 +4+1+1+1+1 +1+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 |