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T65_ALU.vhd
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T65_ALU.vhd
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-- ****
-- T65(b) core. In an effort to merge and maintain bug fixes ....
--
-- See list of changes in T65 top file (T65.vhd)...
--
-- ****
-- 65xx compatible microprocessor core
--
-- FPGAARCADE SVN: $Id: T65_ALU.vhd 2653 2018-06-05 18:14:10Z gary.mups $
--
-- Copyright (c) 2002...2015
-- Daniel Wallner (jesus <at> opencores <dot> org)
-- Mike Johnson (mikej <at> fpgaarcade <dot> com)
-- Wolfgang Scherr (WoS <at> pin4 <dot> at>
-- Morten Leikvoll ()
--
-- All rights reserved
--
-- Redistribution and use in source and synthezised forms, with or without
-- modification, are permitted provided that the following conditions are met:
--
-- Redistributions of source code must retain the above copyright notice,
-- this list of conditions and the following disclaimer.
--
-- Redistributions in synthesized form must reproduce the above copyright
-- notice, this list of conditions and the following disclaimer in the
-- documentation and/or other materials provided with the distribution.
--
-- Neither the name of the author nor the names of other contributors may
-- be used to endorse or promote products derived from this software without
-- specific prior written permission.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
-- THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
-- PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-- POSSIBILITY OF SUCH DAMAGE.
--
-- Please report bugs to the author(s), but before you do so, please
-- make sure that this is not a derivative work and that
-- you have the latest version of this file.
--
-- Limitations :
-- See in T65 top file (T65.vhd)...
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;
use work.T65_Pack.all;
entity T65_ALU is
port(
Mode : in std_logic_vector(1 downto 0); -- "00" => 6502, "01" => 65C02, "10" => 65816
Op : in T_ALU_OP;
BusA : in std_logic_vector(7 downto 0);
BusB : in std_logic_vector(7 downto 0);
P_In : in std_logic_vector(7 downto 0);
P_Out : out std_logic_vector(7 downto 0);
Q : out std_logic_vector(7 downto 0)
);
end T65_ALU;
architecture rtl of T65_ALU is
-- AddSub variables (temporary signals)
signal ADC_Z : std_logic;
signal ADC_C : std_logic;
signal ADC_V : std_logic;
signal ADC_N : std_logic;
signal ADC_Q : std_logic_vector(7 downto 0);
signal SBC_Z : std_logic;
signal SBC_C : std_logic;
signal SBC_V : std_logic;
signal SBC_N : std_logic;
signal SBC_Q : std_logic_vector(7 downto 0);
signal SBX_Q : std_logic_vector(7 downto 0);
begin
process (P_In, BusA, BusB)
variable AL : unsigned(6 downto 0);
variable AH : unsigned(6 downto 0);
variable C : std_logic;
begin
AL := resize(unsigned(BusA(3 downto 0) & P_In(Flag_C)), 7) + resize(unsigned(BusB(3 downto 0) & "1"), 7);
AH := resize(unsigned(BusA(7 downto 4) & AL(5)), 7) + resize(unsigned(BusB(7 downto 4) & "1"), 7);
-- pragma translate_off
if is_x(std_logic_vector(AL)) then AL := "0000000"; end if;
if is_x(std_logic_vector(AH)) then AH := "0000000"; end if;
-- pragma translate_on
if AL(4 downto 1) = 0 and AH(4 downto 1) = 0 then
ADC_Z <= '1';
else
ADC_Z <= '0';
end if;
if AL(5 downto 1) > 9 and P_In(Flag_D) = '1' then
AL(6 downto 1) := AL(6 downto 1) + 6;
end if;
C := AL(6) or AL(5);
AH := resize(unsigned(BusA(7 downto 4) & C), 7) + resize(unsigned(BusB(7 downto 4) & "1"), 7);
ADC_N <= AH(4);
ADC_V <= (AH(4) xor BusA(7)) and not (BusA(7) xor BusB(7));
-- pragma translate_off
if is_x(std_logic_vector(AH)) then AH := "0000000"; end if;
-- pragma translate_on
if AH(5 downto 1) > 9 and P_In(Flag_D) = '1' then
AH(6 downto 1) := AH(6 downto 1) + 6;
end if;
ADC_C <= AH(6) or AH(5);
ADC_Q <= std_logic_vector(AH(4 downto 1) & AL(4 downto 1));
end process;
process (Op, P_In, BusA, BusB)
variable AL : unsigned(6 downto 0);
variable AH : unsigned(5 downto 0);
variable C : std_logic;
variable CT : std_logic;
begin
CT:='0';
if( Op=ALU_OP_AND or --"0001" These OpCodes used to have LSB set
Op=ALU_OP_ADC or --"0011"
Op=ALU_OP_EQ2 or --"0101"
Op=ALU_OP_SBC or --"0111"
Op=ALU_OP_ROL or --"1001"
Op=ALU_OP_ROR or --"1011"
-- Op=ALU_OP_EQ3 or --"1101"
Op=ALU_OP_INC --"1111"
) then
CT:='1';
end if;
C := P_In(Flag_C) or not CT;--was: or not Op(0);
AL := resize(unsigned(BusA(3 downto 0) & C), 7) - resize(unsigned(BusB(3 downto 0) & "1"), 6);
AH := resize(unsigned(BusA(7 downto 4) & "0"), 6) - resize(unsigned(BusB(7 downto 4) & AL(5)), 6);
-- pragma translate_off
if is_x(std_logic_vector(AL)) then AL := "0000000"; end if;
if is_x(std_logic_vector(AH)) then AH := "000000"; end if;
-- pragma translate_on
if AL(4 downto 1) = 0 and AH(4 downto 1) = 0 then
SBC_Z <= '1';
else
SBC_Z <= '0';
end if;
SBC_C <= not AH(5);
SBC_V <= (AH(4) xor BusA(7)) and (BusA(7) xor BusB(7));
SBC_N <= AH(4);
SBX_Q <= std_logic_vector(AH(4 downto 1) & AL(4 downto 1));
if P_In(Flag_D) = '1' then
if AL(5) = '1' then
AL(5 downto 1) := AL(5 downto 1) - 6;
end if;
AH := resize(unsigned(BusA(7 downto 4) & "0"), 6) - resize(unsigned(BusB(7 downto 4) & AL(6)), 6);
if AH(5) = '1' then
AH(5 downto 1) := AH(5 downto 1) - 6;
end if;
end if;
SBC_Q <= std_logic_vector(AH(4 downto 1) & AL(4 downto 1));
end process;
process (Op, P_In, BusA, BusB,
ADC_Z, ADC_C, ADC_V, ADC_N, ADC_Q,
SBC_Z, SBC_C, SBC_V, SBC_N, SBC_Q)
variable Q_t : std_logic_vector(7 downto 0);
variable Q2_t : std_logic_vector(7 downto 0);
begin
-- ORA, AND, EOR, ADC, NOP, LD, CMP, SBC
-- ASL, ROL, LSR, ROR, BIT, LD, DEC, INC
P_Out <= P_In;
Q_t := BusA;
Q2_t := BusA;
case Op is
when ALU_OP_OR=>
Q_t := BusA or BusB;
when ALU_OP_AND=>
Q_t := BusA and BusB;
when ALU_OP_EOR=>
Q_t := BusA xor BusB;
when ALU_OP_ADC=>
P_Out(Flag_V) <= ADC_V;
P_Out(Flag_C) <= ADC_C;
Q_t := ADC_Q;
when ALU_OP_CMP=>
P_Out(Flag_C) <= SBC_C;
when ALU_OP_SAX=>
P_Out(Flag_C) <= SBC_C;
Q_t := SBX_Q; -- undoc: subtract (A & X) - (immediate)
when ALU_OP_SBC=>
P_Out(Flag_V) <= SBC_V;
P_Out(Flag_C) <= SBC_C;
Q_t := SBC_Q; -- undoc: subtract (A & X) - (immediate), then decimal correction
when ALU_OP_ASL=>
Q_t := BusA(6 downto 0) & "0";
P_Out(Flag_C) <= BusA(7);
when ALU_OP_ROL=>
Q_t := BusA(6 downto 0) & P_In(Flag_C);
P_Out(Flag_C) <= BusA(7);
when ALU_OP_LSR=>
Q_t := "0" & BusA(7 downto 1);
P_Out(Flag_C) <= BusA(0);
when ALU_OP_ROR=>
Q_t := P_In(Flag_C) & BusA(7 downto 1);
P_Out(Flag_C) <= BusA(0);
when ALU_OP_ARR=>
Q_t := P_In(Flag_C) & (BusA(7 downto 1) and BusB(7 downto 1));
P_Out(Flag_V) <= Q_t(5) xor Q_t(6);
Q2_t := Q_t;
if P_In(Flag_D)='1' then
if (BusA(3 downto 0) and BusB(3 downto 0)) > "0100" then
Q2_t(3 downto 0) := std_logic_vector(unsigned(Q_t(3 downto 0)) + x"6");
end if;
if (BusA(7 downto 4) and BusB(7 downto 4)) > "0100" then
Q2_t(7 downto 4) := std_logic_vector(unsigned(Q_t(7 downto 4)) + x"6");
P_Out(Flag_C) <= '1';
else
P_Out(Flag_C) <= '0';
end if;
else
P_Out(Flag_C) <= Q_t(6);
end if;
when ALU_OP_BIT=>
P_Out(Flag_V) <= BusB(6);
when ALU_OP_DEC=>
Q_t := std_logic_vector(unsigned(BusA) - 1);
when ALU_OP_INC=>
Q_t := std_logic_vector(unsigned(BusA) + 1);
when others =>
null;
--EQ1,EQ2,EQ3 passes BusA to Q_t and P_in to P_out
end case;
case Op is
when ALU_OP_ADC=>
P_Out(Flag_N) <= ADC_N;
P_Out(Flag_Z) <= ADC_Z;
when ALU_OP_CMP|ALU_OP_SBC|ALU_OP_SAX=>
P_Out(Flag_N) <= SBC_N;
P_Out(Flag_Z) <= SBC_Z;
when ALU_OP_EQ1=>--dont touch P
when ALU_OP_BIT=>
P_Out(Flag_N) <= BusB(7);
if (BusA and BusB) = "00000000" then
P_Out(Flag_Z) <= '1';
else
P_Out(Flag_Z) <= '0';
end if;
when ALU_OP_ANC=>
P_Out(Flag_N) <= Q_t(7);
P_Out(Flag_C) <= Q_t(7);
if Q_t = "00000000" then
P_Out(Flag_Z) <= '1';
else
P_Out(Flag_Z) <= '0';
end if;
when others =>
P_Out(Flag_N) <= Q_t(7);
if Q_t = "00000000" then
P_Out(Flag_Z) <= '1';
else
P_Out(Flag_Z) <= '0';
end if;
end case;
if Op=ALU_OP_ARR then
-- handled above in ARR code
Q <= Q2_t;
else
Q <= Q_t;
end if;
end process;
end;