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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <HTML> <HEAD> <TITLE>html/Listing_of_opc_fetch.vhd</TITLE> <META NAME="generator" CONTENT="HTML::TextToHTML v2.46"> <LINK REL="stylesheet" TYPE="text/css" HREF="lecture.css"> </HEAD> <BODY> <P><table class="ttop"><th class="tpre"><a href="18_Listing_of_opc_deco.vhd.html">Previous Lesson</a></th><th class="ttop"><a href="toc.html">Table of Content</a></th><th class="tnxt"><a href="20_Listing_of_prog_mem_content.vhd.html">Next Lesson</a></th></table> <hr> <H1><A NAME="section_1">19 LISTING OF opc_fetch.vhd</A></H1> <pre class="vhdl"> 1 ------------------------------------------------------------------------------- 2 -- 3 -- Copyright (C) 2009, 2010 Dr. Juergen Sauermann 4 -- 5 -- This code is free software: you can redistribute it and/or modify 6 -- it under the terms of the GNU General Public License as published by 7 -- the Free Software Foundation, either version 3 of the License, or 8 -- (at your option) any later version. 9 -- 10 -- This code is distributed in the hope that it will be useful, 11 -- but WITHOUT ANY WARRANTY; without even the implied warranty of 12 -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 -- GNU General Public License for more details. 14 -- 15 -- You should have received a copy of the GNU General Public License 16 -- along with this code (see the file named COPYING). 17 -- If not, see http://www.gnu.org/licenses/. 18 -- 19 ------------------------------------------------------------------------------- 20 ------------------------------------------------------------------------------- 21 -- 22 -- Module Name: opc_fetch - Behavioral 23 -- Create Date: 13:00:44 10/30/2009 24 -- Description: the opcode fetch stage of a CPU. 25 -- 26 ------------------------------------------------------------------------------- 27 -- 28 library IEEE; 29 use IEEE.std_logic_1164.ALL; 30 use IEEE.std_logic_ARITH.ALL; 31 use IEEE.std_logic_UNSIGNED.ALL; 32 33 entity opc_fetch is 34 port ( I_CLK : in std_logic; 35 36 I_CLR : in std_logic; 37 I_INTVEC : in std_logic_vector( 5 downto 0); 38 I_LOAD_PC : in std_logic; 39 I_NEW_PC : in std_logic_vector(15 downto 0); 40 I_PM_ADR : in std_logic_vector(11 downto 0); 41 I_SKIP : in std_logic; 42 43 Q_OPC : out std_logic_vector(31 downto 0); 44 Q_PC : out std_logic_vector(15 downto 0); 45 Q_PM_DOUT : out std_logic_vector( 7 downto 0); 46 Q_T0 : out std_logic); 47 end opc_fetch; 48 49 architecture Behavioral of opc_fetch is 50 51 component prog_mem 52 port ( I_CLK : in std_logic; 53 54 I_WAIT : in std_logic; 55 I_PC : in std_logic_vector (15 downto 0); 56 I_PM_ADR : in std_logic_vector (11 downto 0); 57 58 Q_OPC : out std_logic_vector (31 downto 0); 59 Q_PC : out std_logic_vector (15 downto 0); 60 Q_PM_DOUT : out std_logic_vector ( 7 downto 0)); 61 end component; 62 63 signal P_OPC : std_logic_vector(31 downto 0); 64 signal P_PC : std_logic_vector(15 downto 0); 65 66 signal L_INVALIDATE : std_logic; 67 signal L_LONG_OP : std_logic; 68 signal L_NEXT_PC : std_logic_vector(15 downto 0); 69 signal L_PC : std_logic_vector(15 downto 0); 70 signal L_T0 : std_logic; 71 signal L_WAIT : std_logic; 72 73 begin 74 75 pmem : prog_mem 76 port map( I_CLK => I_CLK, 77 78 I_WAIT => L_WAIT, 79 I_PC => L_NEXT_PC, 80 I_PM_ADR => I_PM_ADR, 81 82 Q_OPC => P_OPC, 83 Q_PC => P_PC, 84 Q_PM_DOUT => Q_PM_DOUT); 85 86 lpc: process(I_CLK) 87 begin 88 if (rising_edge(I_CLK)) then 89 L_PC <= L_NEXT_PC; 90 L_T0 <= not L_WAIT; 91 end if; 92 end process; 93 94 L_INVALIDATE <= I_CLR or I_SKIP; 95 96 L_NEXT_PC <= X"0000" when (I_CLR = '1') 97 else L_PC when (L_WAIT = '1') 98 else I_NEW_PC when (I_LOAD_PC = '1') 99 else L_PC + X"0002" when (L_LONG_OP = '1') 100 else L_PC + X"0001"; 101 102 -- Two word opcodes: 103 -- 104 -- 9 3210 105 -- 1001 000d dddd 0000 kkkk kkkk kkkk kkkk - LDS 106 -- 1001 001d dddd 0000 kkkk kkkk kkkk kkkk - SDS 107 -- 1001 010k kkkk 110k kkkk kkkk kkkk kkkk - JMP 108 -- 1001 010k kkkk 111k kkkk kkkk kkkk kkkk - CALL 109 -- 110 L_LONG_OP <= '1' when (((P_OPC(15 downto 9) = "1001010") and 111 (P_OPC( 3 downto 2) = "11")) -- JMP, CALL 112 or ((P_OPC(15 downto 10) = "100100") and 113 (P_OPC( 3 downto 0) = "0000"))) -- LDS, STS 114 else '0'; 115 116 -- Two cycle opcodes: 117 -- 118 -- 1001 000d dddd .... - LDS etc. 119 -- 1001 0101 0000 1000 - RET 120 -- 1001 0101 0001 1000 - RETI 121 -- 1001 1001 AAAA Abbb - SBIC 122 -- 1001 1011 AAAA Abbb - SBIS 123 -- 1111 110r rrrr 0bbb - SBRC 124 -- 1111 111r rrrr 0bbb - SBRS 125 126 127 -- 128 L_WAIT <= '0' when (L_INVALIDATE = '1') 129 else '0' when (I_INTVEC(5) = '1') 130 else L_T0 when ((P_OPC(15 downto 9) = "1001000" ) -- LDS etc. 131 or (P_OPC(15 downto 8) = "10010101") -- RET etc. 132 or ((P_OPC(15 downto 10) = "100110") -- SBIC, SBIS 133 and P_OPC(8) = '1') 134 or (P_OPC(15 downto 10) = "111111")) -- SBRC, SBRS 135 else '0'; 136 137 Q_OPC <= X"00000000" when (L_INVALIDATE = '1') 138 else P_OPC when (I_INTVEC(5) = '0') 139 else (X"000000" & "00" & I_INTVEC); -- "interrupt opcode" 140 141 Q_PC <= P_PC; 142 Q_T0 <= L_T0; 143 144 end Behavioral; 145 <pre class="filename"> src/opc_fetch.vhd </pre></pre> <P> <P><hr><BR> <table class="ttop"><th class="tpre"><a href="18_Listing_of_opc_deco.vhd.html">Previous Lesson</a></th><th class="ttop"><a href="toc.html">Table of Content</a></th><th class="tnxt"><a href="20_Listing_of_prog_mem_content.vhd.html">Next Lesson</a></th></table> </BODY> </HTML>
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