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-- Copyright (c)2006, 2011, 2012, 2013, 2015, 2019, 2020 Jeremy Seth Henry
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-- Copyright (c)2006, 2011, 2012, 2013, 2015, 2019, 2020, 2022
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-- Jeremy Seth Henry
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-- All rights reserved.
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-- All rights reserved.
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--
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--
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-- Redistribution and use in source and binary forms, with or without
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-- Redistribution and use in source and binary forms, with or without
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-- modification, are permitted provided that the following conditions are met:
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-- modification, are permitted provided that the following conditions are met:
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-- * Redistributions of source code must retain the above copyright
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-- * Redistributions of source code must retain the above copyright
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-- a constant instead (PSR_GP4). This eliminated the
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-- a constant instead (PSR_GP4). This eliminated the
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-- need to expose an internal constant externally
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-- need to expose an internal constant externally
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-- Seth Henry 05/01/21 Added the Rotate_Ignores_Carry generic, which
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-- Seth Henry 05/01/21 Added the Rotate_Ignores_Carry generic, which
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-- alters the ROR and ROL instructions to behave more
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-- alters the ROR and ROL instructions to behave more
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-- like expected by not rotating through the C flag
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-- like expected by not rotating through the C flag
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-- Seth Henry 07/12/22 Fixed a long-standing bug in the SBC instruction
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-- where the 2's complement inversion wasn't adding
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-- the additional 1, causing off by 1 errors
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library ieee;
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library ieee;
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use ieee.std_logic_1164.all;
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use ieee.std_logic_1164.all;
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use ieee.std_logic_unsigned.all;
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use ieee.std_logic_unsigned.all;
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use ieee.std_logic_arith.all;
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use ieee.std_logic_arith.all;
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Flags(PSR_C) <= Sum(8);
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Flags(PSR_C) <= Sum(8);
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Flags(PSR_N) <= Sum(7);
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Flags(PSR_N) <= Sum(7);
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Regfile(Index) <= Sum(7 downto 0);
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Regfile(Index) <= Sum(7 downto 0);
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when ALU_SBC => -- Rn = R0 - Rn - C : Flags N,C,Z
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when ALU_SBC => -- Rn = R0 - Rn - C : Flags N,C,Z
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Sum := ("0" & Regfile(0)) +
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Sum := ("0" & Regfile(0)) -
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("1" & (not Regfile(Index))) +
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("0" & Regfile(Index)) -
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Flags(PSR_C);
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Flags(PSR_C);
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Flags(PSR_Z) <= nor_reduce(Sum(7 downto 0));
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Flags(PSR_Z) <= nor_reduce(Sum(7 downto 0));
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Flags(PSR_C) <= Sum(8);
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Flags(PSR_C) <= Sum(8);
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Flags(PSR_N) <= Sum(7);
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Flags(PSR_N) <= Sum(7);
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Regfile(0) <= Sum(7 downto 0);
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Regfile(0) <= Sum(7 downto 0);
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