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1 2 poppy 
------------------------------------------------------------------------------------
2 
--                                                                                --
3 
--    Copyright (c) 2004, Hangouet Samuel                                         --
4 
--                  , Jan Sebastien                                               --
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--                  , Mouton Louis-Marie                                          --
6 
--                  , Schneider Olivier     all rights reserved                   --
7 
--                                                                                --
8 
--    This file is part of miniMIPS.                                              --
9 
--                                                                                --
10 
--    miniMIPS is free software; you can redistribute it and/or modify            --
11 5 poppy 
--    it under the terms of the GNU Lesser General Public License as published by --
12 
--    the Free Software Foundation; either version 2.1 of the License, or         --
13 2 poppy 
--    (at your option) any later version.                                         --
14 
--                                                                                --
15 
--    miniMIPS is distributed in the hope that it will be useful,                 --
16 
--    but WITHOUT ANY WARRANTY; without even the implied warranty of              --
17 
--    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               --
18 5 poppy 
--    GNU Lesser General Public License for more details.                         --
19 2 poppy 
--                                                                                --
20 5 poppy 
--    You should have received a copy of the GNU Lesser General Public License    --
21 2 poppy 
--    along with miniMIPS; if not, write to the Free Software                     --
22 
--    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA   --
23 
--                                                                                --
24 
------------------------------------------------------------------------------------
25 
 
26 
 
27 
-- If you encountered any problem, please contact :
28 
--
29 
--   lmouton@enserg.fr
30 
--   oschneid@enserg.fr
31 
--   shangoue@enserg.fr
32 
--
33 
 
34 
 
35 
 
36 
--------------------------------------------------------------------------
37 
--                                                                      --
38 
--                                                                      --
39 
--        Processor miniMIPS : Instruction decoding stage               --
40 
--                                                                      --
41 
--                                                                      --
42 
--                                                                      --
43 
-- Authors : Hangouet  Samuel                                           --
44 
--           Jan       Sébastien                                        --
45 
--           Mouton    Louis-Marie                                      --
46 
--           Schneider Olivier                                          --
47 
--                                                                      --
48 
--                                                          june 2003   --
49 
--------------------------------------------------------------------------
50 
 
51 
library IEEE;
52 
use IEEE.std_logic_1164.all;
53 
use IEEE.numeric_std.all;
54 
 
55 
library work;
56 
use work.pack_mips.all;
57 
 
58 
entity pps_di is
59 
port (
60 
    clock : in std_logic;
61 
    reset : in std_logic;
62 
    stop_all : in std_logic;            -- Unconditionnal locking of the outputs
63 
    clear : in std_logic;               -- Clear the pipeline stage (nop in the outputs)
64 
 
65 
    -- Asynchronous connexion with the register management and data bypass unit
66 
    adr_reg1 : out adr_reg_type;        -- Address of the first register operand
67 
    adr_reg2 : out adr_reg_type;        -- Address of the second register operand
68 
    use1 : out std_logic;               -- Effective use of operand 1
69 
    use2 : out std_logic;               -- Effective use of operand 2
70 
 
71 
    stop_di : in std_logic;             -- Unresolved detected : send nop in the pipeline
72 
    data1 : in bus32;                   -- Operand register 1
73 
    data2 : in bus32;                   -- Operand register 2
74 
 
75 
    -- Datas from EI stage
76 
    EI_adr : in bus32;                  -- Address of the instruction
77 
    EI_instr : in bus32;                -- The instruction to decode
78 
    EI_it_ok : in std_logic;            -- Allow hardware interruptions
79 
 
80 
    -- Synchronous output to EX stage
81 
    DI_bra : out std_logic;             -- Branch decoded
82 
    DI_link : out std_logic;            -- A link for that instruction
83 
    DI_op1 : out bus32;                 -- operand 1 for alu
84 
    DI_op2 : out bus32;                 -- operand 2 for alu
85 
    DI_code_ual : out alu_ctrl_type;    -- Alu operation
86 
    DI_offset : out bus32;              -- Offset for the address calculation
87 
    DI_adr_reg_dest : out adr_reg_type; -- Address of the destination register of the result
88 
    DI_ecr_reg : out std_logic;         -- Effective writing of the result
89 
    DI_mode : out std_logic;            -- Address mode (relative to pc or indexed to a register)
90 
    DI_op_mem : out std_logic;          -- Memory operation request
91 
    DI_r_w : out std_logic;             -- Type of memory operation (reading or writing)
92 
    DI_adr : out bus32;                 -- Address of the decoded instruction
93 
    DI_exc_cause : out bus32;           -- Potential exception detected
94 
    DI_level : out level_type;          -- Availability of the result for the data bypass
95 
    DI_it_ok : out std_logic            -- Allow hardware interruptions
96 
);
97 
end entity;
98 
 
99 
 
100 
architecture rtl of pps_di is
101 
 
102 
    -- Enumeration type used for the micro-code of the instruction
103 
    type op_mode_type is (OP_NORMAL, OP_SPECIAL, OP_REGIMM, OP_COP0);   -- selection du mode de l'instruction
104 
    type off_sel_type is (OFS_PCRL, OFS_NULL, OFS_SESH, OFS_SEXT);      -- selection de la valeur de l'offset
105 
    type rdest_type is ( D_RT, D_RD, D_31, D_00);                       -- selection du registre destination
106 
 
107 
    -- Record type containg the micro-code of an instruction
108 
    type micro_instr_type is
109 
    record
110 
        op_mode : op_mode_type;    -- Instruction codop mode
111 
        op_code : bus6;            -- Instruction codop
112 
        bra : std_logic;           -- Branch instruction
113 
        link : std_logic;          -- Branch with link : the return address is saved in a register
114 
        code_ual : alu_ctrl_type;  -- Operation code for the alu
115 
        op_mem : std_logic;        -- Memory operation needed
116 
        r_w : std_logic;           -- Read/Write selection in memory
117 
        mode : std_logic;          -- Address calculation from the current pc ('1') or the alu operand 1 ('0')
118 
        off_sel : off_sel_type;    -- Offset source : PC(31..28) & Adresse & 00 || 0 || sgn_ext(Imm) & 00 || sgn_ext(Imm)
119 
        exc_cause : bus32;         -- Unconditionnal exception cause to generate
120 
        cop_org1 : std_logic;      -- Source register 1 : general register if 0, coprocessor register if 1
121 
        cop_org2 : std_logic;      -- Source register 2 : general register if 0, coprocessor register if 1
122 
        cs_imm1 : std_logic;       -- Use of immediat operand 1 instead of register bank
123 
        cs_imm2 : std_logic;       -- Use of immediat operand 2 instead of register bank
124 
        imm1_sel : std_logic;      -- Origine of immediat operand 1
125 
        imm2_sel : std_logic;      -- Origine of immediat operand 2
126 
        level : level_type;        -- Data availability stage for the bypass
127 
        ecr_reg : std_logic;       -- Writing the result in a register
128 
        bank_des : std_logic;      -- Register bank selection : GPR if 0, coprocessor system if 1
129 
        des_sel : rdest_type ;     -- Destination register address : Rt, Rd, $31, $0
130 
    end record;
131 
 
132 
    type micro_code_type is array (natural range <>) of micro_instr_type;
133 
 
134 
    constant micro_code : micro_code_type :=
135 
( -- Instruction decoding in micro-instructions table
136 
(OP_SPECIAL, "100000", '0', '0', OP_ADD  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- ADD
137 
(OP_NORMAL , "001000", '0', '0', OP_ADD  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '1', LVL_EX , '1', '0', D_RT), -- ADDI
138 
(OP_NORMAL , "001001", '0', '0', OP_ADDU , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_RT), -- ADDIU
139 
(OP_SPECIAL, "100001", '0', '0', OP_ADDU , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- ADDU
140 
(OP_SPECIAL, "100100", '0', '0', OP_AND  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- AND
141 
(OP_NORMAL , "001100", '0', '0', OP_AND  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_RT), -- ANDI
142 
(OP_NORMAL , "000100", '1', '0', OP_EQU  , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_DI , '0', '0', D_RT), -- BEQ
143 
(OP_REGIMM , "000001", '1', '0', OP_LPOS , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- BGEZ
144 
(OP_REGIMM , "010001", '1', '1', OP_LPOS , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_31), -- BGEZAL
145 
(OP_NORMAL , "000111", '1', '0', OP_SPOS , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- BGTZ
146 
(OP_NORMAL , "000110", '1', '0', OP_LNEG , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- BLEZ
147 
(OP_REGIMM , "000000", '1', '0', OP_SNEG , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- BLTZ
148 
(OP_REGIMM , "010000", '1', '1', OP_SNEG , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_31), -- BLTZAL
149 
(OP_NORMAL , "000101", '1', '0', OP_NEQU , '0', '0', '1', OFS_SESH, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_DI , '0', '0', D_RT), -- BNE
150 
(OP_SPECIAL, "001101", '0', '0', OP_OUI  , '0', '0', '0', OFS_PCRL, IT_BREAK, '0', '0', '1', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- BREAK
151 
(OP_COP0   , "000001", '0', '0', OP_OP2  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_DI , '1', '1', D_00), -- COP0
152 
(OP_NORMAL , "000010", '1', '0', OP_OUI  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- J
153 
(OP_NORMAL , "000011", '1', '1', OP_OUI  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_EX , '1', '0', D_31), -- JAL
154 
(OP_SPECIAL, "001001", '1', '1', OP_OUI  , '0', '0', '0', OFS_NULL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_RD), -- JALR
155 
(OP_SPECIAL, "001000", '1', '0', OP_OUI  , '0', '0', '0', OFS_NULL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- JR
156 
(OP_NORMAL , "001111", '0', '0', OP_LUI  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_EX , '1', '0', D_RT), -- LUI
157 
(OP_NORMAL , "100011", '0', '0', OP_OUI  , '1', '0', '0', OFS_SEXT, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_MEM, '1', '0', D_RT), -- LW
158 
(OP_NORMAL , "110000", '0', '0', OP_OUI  , '1', '0', '0', OFS_SEXT, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_MEM, '1', '1', D_RT), -- LWC0
159 
(OP_COP0   , "000000", '0', '0', OP_OP2    , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '1', '1', '0', '0', '0', LVL_DI , '1', '0', D_RD), -- MFC0
160 
(OP_SPECIAL, "010000", '0', '0', OP_MFHI , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_EX , '1', '0', D_RD), -- MFHI
161 
(OP_SPECIAL, "010010", '0', '0', OP_MFLO , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '1', '0', '0', LVL_EX , '1', '0', D_RD), -- MFLO
162 
(OP_COP0   , "000100", '0', '0', OP_OP2  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '0', '0', '0', LVL_DI , '1', '1', D_RD), -- MTC0
163 
(OP_SPECIAL, "010001", '0', '0', OP_MTHI , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- MTHI
164 
(OP_SPECIAL, "010011", '0', '0', OP_MTLO , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- MTLO
165 
(OP_SPECIAL, "011000", '0', '0', OP_MULT , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '0', '0', D_RT), -- MULT
166 
(OP_SPECIAL, "011001", '0', '0', OP_MULTU, '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '0', '0', D_RT), -- MULT
167 
(OP_SPECIAL, "100111", '0', '0', OP_NOR  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- NOR
168 
(OP_SPECIAL, "100101", '0', '0', OP_OR   , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- OR
169 
(OP_NORMAL , "001101", '0', '0', OP_OR   , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_RT), -- ORI
170 
(OP_SPECIAL, "000000", '0', '0', OP_SLL  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '0', '1', '0', LVL_EX , '1', '0', D_RD), -- SLL
171 
(OP_SPECIAL, "000100", '0', '0', OP_SLL  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SLLV
172 
(OP_SPECIAL, "101010", '0', '0', OP_SLT  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SLT
173 
(OP_NORMAL , "001010", '0', '0', OP_SLT  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '1', LVL_EX , '1', '0', D_RT), -- SLTI
174 
(OP_NORMAL , "001011", '0', '0', OP_SLTU , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '1', LVL_EX , '1', '0', D_RT), -- SLTIU
175 
(OP_SPECIAL, "101011", '0', '0', OP_SLTU , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SLTU
176 
(OP_SPECIAL, "000011", '0', '0', OP_SRA  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '0', '1', '0', LVL_EX , '1', '0', D_RD), -- SRA
177 
(OP_SPECIAL, "000111", '0', '0', OP_SRA  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SRAV
178 
(OP_SPECIAL, "000010", '0', '0', OP_SRL  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '1', '0', '1', '0', LVL_EX , '1', '0', D_RD), -- SRL
179 
(OP_SPECIAL, "000110", '0', '0', OP_SRL  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SRLV
180 
(OP_SPECIAL, "100010", '0', '0', OP_SUB  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SUB
181 
(OP_SPECIAL, "100011", '0', '0', OP_SUBU , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- SUBU
182 
(OP_NORMAL , "101011", '0', '0', OP_OP2  , '1', '1', '0', OFS_SEXT, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_DI , '0', '0', D_RT), -- SW
183 
(OP_NORMAL , "111000", '0', '0', OP_OP2  , '1', '1', '0', OFS_SEXT, IT_NOEXC, '0', '1', '0', '0', '0', '0', LVL_DI , '0', '0', D_RT), -- SWC0
184 
(OP_SPECIAL, "001100", '0', '0', OP_OUI  , '0', '0', '0', OFS_PCRL, IT_SCALL, '0', '0', '1', '1', '0', '0', LVL_DI , '0', '0', D_RT), -- SYSC
185 
(OP_SPECIAL, "100110", '0', '0', OP_XOR  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '0', '0', '0', LVL_EX , '1', '0', D_RD), -- XOR
186 
(OP_NORMAL , "001110", '0', '0', OP_XOR  , '0', '0', '0', OFS_PCRL, IT_NOEXC, '0', '0', '0', '1', '0', '0', LVL_EX , '1', '0', D_RT)  -- XORI
187 
);
188 
 
189 
    -- Preparation of the synchronous outputs
190 
    signal PRE_bra : std_logic;             -- Branch operation
191 
    signal PRE_link : std_logic;            -- Branch with link
192 
    signal PRE_op1 : bus32;                 -- operand 1 of the ual
193 
    signal PRE_op2 : bus32;                 -- operand 2 of the ual
194 
    signal PRE_code_ual : alu_ctrl_type;    -- Alu operation
195 
    signal PRE_offset : bus32;              -- Address offset for calculation
196 
    signal PRE_adr_reg_dest : adr_reg_type; -- Destination register adress for result
197 
    signal PRE_ecr_reg : std_logic;         -- Writing of result in the bank register
198 
    signal PRE_mode : std_logic;            -- Address calculation with current pc
199 
    signal PRE_op_mem : std_logic;          -- Memory access operation instruction
200 
    signal PRE_r_w : std_logic;             -- Read/write selection in memory
201 
    signal PRE_exc_cause : bus32;           -- Potential exception cause
202 
    signal PRE_level : level_type;          -- Result availability stage for bypass
203 
 
204 
begin
205 
 
206 
 
207 
    -- Instruction decoding
208 
    process (EI_instr, EI_adr, data1, data2)
209 
        variable op_code : bus6;             -- Effective codop of the instruction
210 
        variable op_mode : op_mode_type;     -- Instruction mode
211 
        variable flag : boolean;             -- Is true if valid instruction
212 
        variable instr : integer;            -- Current micro-instruction adress
213 
 
214 
        -- Instruction fields
215 
        variable rs : bus5;
216 
        variable rt : bus5;
217 
        variable rd : bus5;
218 
        variable shamt : bus5;
219 
        variable imm : bus16;
220 
        variable address : bus26;
221 
    begin
222 
 
223 
        -- Selection of the instruction codop and its mode
224 
        case EI_instr(31 downto 26) is
225 
            when "000000" => -- special mode
226 
                op_mode := OP_SPECIAL;
227 
                op_code := EI_instr(5 downto 0);
228 
            when "000001" => -- regimm mode
229 
                op_mode := OP_REGIMM;
230 
                op_code := '0' & EI_instr(20 downto 16);
231 
            when "010000" => -- cop0 mode
232 
                op_mode := OP_COP0;
233 
                op_code := '0' & EI_instr(25 downto 21);
234 
            when others   => -- normal mode
235 
                op_mode := OP_NORMAL;
236 
                op_code := EI_instr(31 downto 26);
237 
        end case;
238 
 
239 
 
240 
        -- Search the current instruction in the micro-code table
241 
        flag := false;
242 
        instr := 0;
243 
        for i in micro_code'range loop
244 
            if micro_code(i).op_mode=op_mode and micro_code(i).op_code=op_code then
245 
                flag := true;           -- The instruction exists
246 
                instr := i;             -- Index memorisation
247 
            end if;
248 
        end loop;
249 
 
250 
        -- Read the instruction field
251 
        rs      := EI_instr(25 downto 21);
252 
        rt      := EI_instr(20 downto 16);
253 
        rd      := EI_instr(15 downto 11);
254 
        shamt   := EI_instr(10 downto  6);
255 
        imm     := EI_instr(15 downto  0);
256 
        address := EI_instr(25 downto  0);
257 
 
258 
        if not flag then -- Unknown instruction
259 
 
260 
            -- Synchronous output preparation
261 
            PRE_bra          <= '0';              -- Branch operation
262 
            PRE_link         <= '0';              -- Branch with link
263 
            PRE_op1          <= (others => '0');  -- operand 1 of the ual
264 
            PRE_op2          <= (others => '0');  -- operand 2 of the ual
265 
            PRE_code_ual     <= OP_OUI;           -- Alu operation
266 
            PRE_offset       <= (others => '0');  -- Address offset for calculation
267 
            PRE_adr_reg_dest <= (others => '0');  -- Destination register adress for result
268 
            PRE_ecr_reg      <= '0';              -- Writing of result in the bank register
269 
            PRE_mode         <= '0';              -- Address calculation with current pc
270 
            PRE_op_mem       <= '0';              -- Memory access operation instruction
271 
            PRE_r_w          <= '0';              -- Read/write selection in memory
272 
            PRE_exc_cause    <= IT_ERINS;         -- Potential exception cause
273 
            PRE_level        <= LVL_DI;           -- Result availability stage for bypass
274 
 
275 
            -- Set asynchronous outputs
276 
            adr_reg1 <= (others => '0');    -- First operand register
277 
            adr_reg2 <= (others => '0');    -- Second operand register
278 
            use1 <= '0';                    -- Effective use of operand 1
279 
            use2 <= '0';                    -- Effective use of operand 2
280 
 
281 
        else -- Valid instruction
282 
 
283 
            -- Offset signal preparation
284 
            case micro_code(instr).off_sel is
285 
                when OFS_PCRL => -- PC(31..28) & Adresse & 00
286 
                    PRE_offset <= EI_adr(31 downto 28) & address & "00";
287 
                when OFS_NULL => -- 0
288 
                    PRE_offset <= (others => '0');
289 
                when OFS_SESH => -- sgn_ext(Imm) & 00
290 
                    if imm(15)='1' then
291 
                        PRE_offset <= "11111111111111" & imm & "00";
292 
                    else
293 
                        PRE_offset <= "00000000000000" & imm & "00";
294 
                    end if;
295 
                when OFS_SEXT => -- sgn_ext(Imm)
296 
                    if imm(15)='1' then
297 
                        PRE_offset <= "1111111111111111" & imm;
298 
                    else
299 
                        PRE_offset <= "0000000000000000" & imm;
300 
                    end if;
301 
            end case;
302 
 
303 
 
304 
            -- Alu operand preparation
305 
            if micro_code(instr).cs_imm1='0' then
306 
                -- Datas from register banks
307 
                PRE_op1 <= data1;
308 
            else
309 
                -- Immediate datas
310 
                if micro_code(instr).imm1_sel='0' then
311 
                    PRE_op1 <= (others => '0');             -- Immediate operand = 0
312 
                else
313 
                    PRE_op1 <= X"000000" & "000" & shamt;   -- Immediate operand = shamt
314 
                end if;
315 
            end if;
316 
 
317 
 
318 
            if micro_code(instr).cs_imm2='0' then
319 
                -- Datas from register banks
320 
                PRE_op2 <= data2;
321 
            else
322 
                -- Immediate datas
323 
                if micro_code(instr).imm2_sel='0' then
324 
                    PRE_op2 <= X"0000" & imm;               -- Immediate operand = imm
325 
                else
326 
                    if imm(15)='1' then                     -- Immediate operand = sgn_ext(imm)
327 
                        PRE_op2 <= X"FFFF" & imm;
328 
                    else
329 
                        PRE_op2 <= X"0000" & imm;
330 
                    end if;
331 
                end if;
332 
            end if;
333 
 
334 
            -- Selection of destination register address
335 
            case micro_code(instr).des_sel is
336 
                when D_RT => PRE_adr_reg_dest <= micro_code(instr).bank_des & rt;
337 
                when D_RD => PRE_adr_reg_dest <= micro_code(instr).bank_des & rd;
338 
                when D_31 => PRE_adr_reg_dest <= micro_code(instr).bank_des & "11111";
339 
                when D_00 => PRE_adr_reg_dest <= micro_code(instr).bank_des & "00000";
340 
            end case;
341 
 
342 
            -- Command signal affectation
343 
            PRE_bra       <= micro_code(instr).bra;        -- Branch operation
344 
            PRE_link      <= micro_code(instr).link;       -- Branch with link
345 
            PRE_code_ual  <= micro_code(instr).code_ual;   -- Alu operation
346 
            PRE_ecr_reg   <= micro_code(instr).ecr_reg;    -- Writing the result in a bank register
347 
            PRE_mode      <= micro_code(instr).mode;       -- Type of calculation for the address with current pc
348 
            PRE_op_mem    <= micro_code(instr).op_mem;     -- Memory operation needed
349 
            PRE_r_w       <= micro_code(instr).r_w;        -- Read/Write in memory selection
350 
            PRE_exc_cause <= micro_code(instr).exc_cause;  -- Potential cause exception
351 
            PRE_level     <= micro_code(instr).level;
352 
 
353 
            -- Set asynchronous outputs
354 
            adr_reg1 <= micro_code(instr).cop_org1 & rs; -- First operand register address
355 
            adr_reg2 <= micro_code(instr).cop_org2 & rt; -- Second operand register address
356 
            use1 <= not micro_code(instr).cs_imm1;       -- Effective use of operande 1
357 
            use2 <= not micro_code(instr).cs_imm2;       -- Effective use of operande 2
358 
        end if;
359 
 
360 
    end process;
361 
 
362 
 
363 
 
364 
    -- Set the synchronous outputs
365 
    process (clock)
366 
    begin
367 
        if clock='1' and clock'event then
368 
            if reset='1' then
369 
                DI_bra <= '0';
370 
                DI_link <= '0';
371 
                DI_op1 <= (others => '0');
372 
                DI_op2 <= (others => '0');
373 
                DI_code_ual <= OP_OUI;
374 
                DI_offset <= (others => '0');
375 
                DI_adr_reg_dest <= (others => '0');
376 
                DI_ecr_reg <= '0';
377 
                DI_mode <= '0';
378 
                DI_op_mem <= '0';
379 
                DI_r_w <= '0';
380 
                DI_adr <= (others => '0');
381 
                DI_exc_cause <= IT_NOEXC;
382 
                DI_level <= LVL_DI;
383 
                DI_it_ok <= '0';
384 
            elsif stop_all='0' then
385 
                if clear='1' or stop_di='1' then
386 
                    -- Nop instruction
387 
                    DI_bra <= '0';
388 
                    DI_link <= '0';
389 
                    DI_op1 <= (others => '0');
390 
                    DI_op2 <= (others => '0');
391 
                    DI_code_ual <= OP_OUI;
392 
                    DI_offset <= (others => '0');
393 
                    DI_adr_reg_dest <= (others => '0');
394 
                    DI_ecr_reg <= '0';
395 
                    DI_mode <= '0';
396 
                    DI_op_mem <= '0';
397 
                    DI_r_w <= '0';
398 
                    DI_adr <= EI_adr;
399 
                    DI_exc_cause <= IT_NOEXC;
400 
                    DI_level <= LVL_DI;
401 
                    if clear='1' then
402 
                      DI_it_ok <= '0';
403 
                    else
404 
                      DI_it_ok <= EI_it_ok;
405 
                    end if;
406 
                else -- Noraml step
407 
                    DI_bra <= PRE_bra;
408 
                    DI_link <= PRE_link;
409 
                    DI_op1 <= PRE_op1;
410 
                    DI_op2 <= PRE_op2;
411 
                    DI_code_ual <= PRE_code_ual;
412 
                    DI_offset <= PRE_offset;
413 
                    DI_adr_reg_dest <= PRE_adr_reg_dest;
414 
                    DI_ecr_reg <= PRE_ecr_reg;
415 
                    DI_mode <= PRE_mode;
416 
                    DI_op_mem <= PRE_op_mem;
417 
                    DI_r_w <= PRE_r_w;
418 
                    DI_adr <= EI_adr;
419 
                    DI_exc_cause <= PRE_exc_cause;
420 
                    DI_level <= PRE_level;
421 
                    DI_it_ok <= EI_it_ok;
422 
                end if;
423 
            end if;
424 
        end if;
425 
    end process;
426 
 
427 
end rtl;
428 
 
429 
 

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