74 lines
2.5 KiB
Ruby
74 lines
2.5 KiB
Ruby
require "asm/nodes"
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module Asm
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# ADDRESSING MODE 2
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# Implemented: immediate offset with offset=0
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class MemoryAccessBuilder
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include Asm::InstructionTools
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def initialize(inst_class, byte_access, load_store)
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@cond = 0b1110
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@inst_class = 0
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@i = 0 #I flag (third bit)
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@pre_post_index = 0 #P flag
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@add_offset = 0 #U flag
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@byte_access = 0 #B flag
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@w = 0 #W flag
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@load_store = 0 #L flag
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@rn = 0
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@rd = 0
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@operand = 0
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@inst_class = inst_class
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@byte_access = byte_access
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@load_store = load_store
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end
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attr_accessor :cond, :inst_class, :i, :pre_post_index, :add_offset,
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:byte_access, :w, :load_store, :rn, :rd, :operand
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# Build representation for target address
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def build_operand(arg)
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#str / ldr are _serious instructions. With BIG possibilities not half are implemented
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@i = 0
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@pre_post_index = 0
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@w = 0
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@operand = 0
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if (arg.is_a?(Asm::Register))
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@rn = reg_ref(arg)
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if(arg.offset != 0)
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@operand = arg.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 Asm::AssemblyError.new("reference offset too large/small (max 4095) #{argr.right}" )
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end
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end
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elsif (arg.is_a?(Asm::Label) or arg.is_a?(Asm::NumLiteral))
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@pre_post_index = 1
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@rn = 15 # 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 Asm::AssemblyError.new("invalid operand argument #{arg.inspect}")
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end
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end
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def assemble(io, as, inst)
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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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val = operand | (rd << 12 ) | (rn << 12 + 4) |
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(load_store << 12+4+4) | (w << 12+4+4+1) |
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(byte_access << 12+4+4+1+1) | (add_offset << 12+4+4+1+1+1) |
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(pre_post_index << 12+4+4+1+1+1+1) | (i << 12+4+4+1+1+1+1+1) |
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(inst_class << 12+4+4+1+1+1+1+1+1) | (cond << 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 |