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-- $Id: pdp11_aunit.vhd 330 2010-09-19 17:43:53Z mueller $ -- -- Copyright 2006-2007 by Walter F.J. Mueller <W.F.J.Mueller@gsi.de> -- -- This program is free software; you may redistribute and/or modify it under -- the terms of the GNU General Public License as published by the Free -- Software Foundation, either version 2, or at your option any later version. -- -- This program is distributed in the hope that it will be useful, but -- WITHOUT ANY WARRANTY, without even the implied warranty of MERCHANTABILITY -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- for complete details. -- ------------------------------------------------------------------------------ -- Module Name: pdp11_aunit - syn -- Description: pdp11: arithmetic unit for data (aunit) -- -- Dependencies: - -- Test bench: tb/tb_pdp11_core (implicit) -- Target Devices: generic -- Tool versions: xst 8.1, 8.2, 9.1, 9.2, 12.1; ghdl 0.18-0.26 -- Revision History: -- Date Rev Version Comment -- 2010-09-18 300 1.1 renamed from abox -- 2007-06-14 56 1.0.1 Use slvtypes.all -- 2007-05-12 26 1.0 Initial version ------------------------------------------------------------------------------ library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; use ieee.std_logic_unsigned.all; use work.slvtypes.all; use work.pdp11.all; -- ---------------------------------------------------------------------------- -- arithmetic unit for data, usage: -- ADD: SRC + DST + 0 (dst+src) -- SUB: ~SRC + DST + 1 (dst-src) -- ADC: 0 + DST + CI (dst+ci) -- SBC: ~0 + DST + ~CI (dst-ci) -- CMP: SRC + ~DST + 1 (src-dst) -- COM: 0 + ~DST + 0 (~dst) -- NEG: 0 + ~DST + 1 (-dst) -- INC: 0 + DST + 1 (dst+1) -- DEC: ~0 + DST + 0 (dst-1) -- CLR: 0 + 0 + 0 (0) -- SOB: SRC + ~0 + 0 (src-1) entity pdp11_aunit is -- arithmetic unit for data (aunit) port ( DSRC : in slv16; -- 'src' data in DDST : in slv16; -- 'dst' data in CI : in slbit; -- carry flag in SRCMOD : in slv2; -- src modifier mode DSTMOD : in slv2; -- dst modifier mode CIMOD : in slv2; -- ci modifier mode CC1OP : in slbit; -- use cc modes (1 op instruction) CCMODE : in slv3; -- cc mode BYTOP : in slbit; -- byte operation DOUT : out slv16; -- data output CCOUT : out slv4 -- condition codes out ); end pdp11_aunit; architecture syn of pdp11_aunit is -- -------------------------------------- begin process (DSRC, DDST, CI, CIMOD, CC1OP, CCMODE, SRCMOD, DSTMOD, BYTOP) variable msrc : slv16 := (others=>'0'); -- effective src data variable mdst : slv16 := (others=>'0'); -- effective dst data variable mci : slbit := '0'; -- effective ci variable sum : slv16 := (others=>'0'); -- sum variable co8 : slbit := '0'; -- co 8 bit variable co16 : slbit := '0'; -- co 16 bit variable nno : slbit := '0'; -- local no variable nzo : slbit := '0'; -- local zo variable nvo : slbit := '0'; -- local vo variable nco : slbit := '0'; -- local co variable src_msb : slbit := '0'; -- msb from src (bit 15 or 7) variable dst_msb : slbit := '0'; -- msb from dst (bit 15 or 7) variable sum_msb : slbit := '0'; -- msb from sum (bit 15 or 7) alias NO : slbit is CCOUT(3); alias ZO : slbit is CCOUT(2); alias VO : slbit is CCOUT(1); alias CO : slbit is CCOUT(0); -- procedure do_add8_ci_co: 8 bit adder with carry in and carry out -- implemented following the recommended pattern for XST ISE V8.1 procedure do_add8_ci_co ( variable a : in slv8; -- input a variable b : in slv8; -- input b variable ci : in slbit; -- carry in variable sum : out slv8; -- sum out variable co : out slbit -- carry out ) is variable tmp: slv9; begin tmp := conv_std_logic_vector((conv_integer(a) + conv_integer(b) + conv_integer(ci)),9); sum := tmp(7 downto 0); co := tmp(8); end procedure do_add8_ci_co; begin case SRCMOD is when c_aunit_mod_pass => msrc := DSRC; when c_aunit_mod_inv => msrc := not DSRC; when c_aunit_mod_zero => msrc := (others=>'0'); when c_aunit_mod_one => msrc := (others=>'1'); when others => null; end case; case DSTMOD is when c_aunit_mod_pass => mdst := DDST; when c_aunit_mod_inv => mdst := not DDST; when c_aunit_mod_zero => mdst := (others=>'0'); when c_aunit_mod_one => mdst := (others=>'1'); when others => null; end case; case CIMOD is when c_aunit_mod_pass => mci := CI; when c_aunit_mod_inv => mci := not CI; when c_aunit_mod_zero => mci := '0'; when c_aunit_mod_one => mci := '1'; when others => null; end case; do_add8_ci_co(msrc(7 downto 0), mdst(7 downto 0), mci, sum(7 downto 0), co8); do_add8_ci_co(msrc(15 downto 8), mdst(15 downto 8), co8, sum(15 downto 8), co16); DOUT <= sum; -- V ('overflow) bit set if -- ADD : both operants of same sign but has result opposite sign -- SUB : both operants of opposide sign and sign source equals sign result -- CMP : both operants of opposide sign and sign dest. equals sign result nno := '0'; nzo := '0'; nvo := '0'; nco := '0'; if BYTOP = '1' then nno := sum(7); if unsigned(sum(7 downto 0)) = 0 then nzo := '1'; else nzo := '0'; end if; nco := co8; src_msb := DSRC(7); dst_msb := DDST(7); sum_msb := sum(7); else nno := sum(15); if unsigned(sum) = 0 then nzo := '1'; else nzo := '0'; end if; nco := co16; src_msb := DSRC(15); dst_msb := DDST(15); sum_msb := sum(15); end if; -- the logic for 2 operand V+C is ugly. It is reverse engineered from -- the MOD's the operation type. if CC1OP = '0' then -- 2 operand cases if unsigned(CIMOD) = unsigned(c_aunit_mod_zero) then -- case ADD nvo := not(src_msb xor dst_msb) and (src_msb xor sum_msb); else if unsigned(SRCMOD) = unsigned(c_aunit_mod_inv) then -- case SUB nvo := (src_msb xor dst_msb) and not (src_msb xor sum_msb); else -- case CMP nvo := (src_msb xor dst_msb) and not (dst_msb xor sum_msb); end if; nco := not nco; -- invert C for SUB and CMP end if; else -- 1 operand cases case CCMODE is when c_aunit_ccmode_clr|c_aunit_ccmode_tst => nvo := '0'; -- force v=0 for tst and clr nco := '0'; -- force c=0 for tst and clr when c_aunit_ccmode_com => nvo := '0'; -- force v=0 for com nco := '1'; -- force c=1 for com when c_aunit_ccmode_inc => nvo := sum_msb and not dst_msb; nco := CI; -- C not affected for INC when c_aunit_ccmode_dec => nvo := not sum_msb and dst_msb; nco := CI; -- C not affected for DEC when c_aunit_ccmode_neg => nvo := sum_msb and dst_msb; nco := not nzo; when c_aunit_ccmode_adc => nvo := sum_msb and not dst_msb; when c_aunit_ccmode_sbc => nvo := not sum_msb and dst_msb; nco := not nco; when others => null; end case; end if; NO <= nno; ZO <= nzo; VO <= nvo; CO <= nco; end process; end syn;
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