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[/] [pdp8/] [trunk/] [pdp8/] [cpu/] [mqa.vhd] - Rev 6
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------------------------------------------------------------------ --! --! PDP-8 Processor --! --! \brief --! CPU Multiplier Quotient Auxillary Register (MQA) --! --! \details --! The Multiplier Quotient Auxillary Register (MQA) is a --! temporary register used during EAE shift and divide --! instructions. --! --! \todo --! Is the MQA register really necessary? Can it be --! deleted and the instructions be re-written? --! --! \file --! mqa.vhd --! --! \author --! Rob Doyle - doyle (at) cox (dot) net --! -------------------------------------------------------------------- -- -- Copyright (C) 2009, 2010, 2011 Rob Doyle -- -- This source file may be used and distributed without -- restriction provided that this copyright statement is not -- removed from the file and that any derivative work contains -- the original copyright notice and the associated disclaimer. -- -- This source file is free software; you can redistribute it -- and/or modify it under the terms of the GNU Lesser General -- Public License as published by the Free Software Foundation; -- version 2.1 of the License. -- -- This source 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 Lesser General Public License for more -- details. -- -- You should have received a copy of the GNU Lesser General -- Public License along with this source; if not, download it -- from http://www.gnu.org/licenses/lgpl.txt -- -------------------------------------------------------------------- -- -- Comments are formatted for doxygen -- library ieee; --! IEEE Library use ieee.std_logic_1164.all; --! IEEE 1164 use work.cpu_types.all; --! Types -- --! CPU Auxillary Multiplier Quotient Register (MQA) Entity -- entity eMQA is port ( sys : in sys_t; --! Clock/Reset mqaOP : in mqaop_t; --! MQA Operation MQ : in data_t; --! MQ Register MQA : out data_t --! MQA Output ); end eMQA; -- --! CPU Auxillary Multiplier Quotient Register (MQA) RTL -- architecture rtl of eMQA is signal mqaREG : data_t; --! Aux Multiplier Quotient Register signal mqaMUX : data_t; --! Aux Multiplier Quotient Multiplexer begin -- -- MQ Multiplexer -- with mqaOP select mqaMUX <= mqaREG when mqaopNOP, -- MQA <- MQ o"0000" when mqaopCLR, -- MQA <- "0000" MQ when mqaopMQ, -- MQA <- MQ mqaREG(1 to 11) & '0' when mqaopSHL; -- MQA <- (MQA << 1) -- --! MQA Register -- REG_MQA : process(sys) begin if sys.rst = '1' then mqaREG <= o"0000"; elsif rising_edge(sys.clk) then mqaREG <= mqaMUX; end if; end process REG_MQA; MQA <= mqaREG; end rtl;
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