diff options
Diffstat (limited to 'sn76489-1.0/sn76489_latch_ctrl.vhd')
| -rw-r--r-- | sn76489-1.0/sn76489_latch_ctrl.vhd | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/sn76489-1.0/sn76489_latch_ctrl.vhd b/sn76489-1.0/sn76489_latch_ctrl.vhd new file mode 100644 index 0000000..789720c --- /dev/null +++ b/sn76489-1.0/sn76489_latch_ctrl.vhd @@ -0,0 +1,138 @@ +------------------------------------------------------------------------------- +-- +-- Synthesizable model of TI's SN76489AN. +-- +-- $Id: sn76489_latch_ctrl.vhd,v 1.6 2006/02/27 20:30:10 arnim Exp $ +-- +-- Latch Control Unit +-- +------------------------------------------------------------------------------- +-- +-- Copyright (c) 2005, 2006, Arnim Laeuger (arnim.laeuger@gmx.net) +-- +-- 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, 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. +-- +------------------------------------------------------------------------------- + +library ieee; +use ieee.std_logic_1164.all; + +entity sn76489_latch_ctrl is + + port ( + clock_i : in std_logic; + clk_en_i : in boolean; + res_n_i : in std_logic; + ce_n_i : in std_logic; + we_n_i : in std_logic; + d_i : in std_logic_vector(0 to 7); + ready_o : out std_logic; + tone1_we_o : out boolean; + tone2_we_o : out boolean; + tone3_we_o : out boolean; + noise_we_o : out boolean; + r2_o : out std_logic + ); + +end sn76489_latch_ctrl; + + +library ieee; +use ieee.numeric_std.all; + +architecture rtl of sn76489_latch_ctrl is + + signal reg_q : std_logic_vector(0 to 2); + signal we_q : boolean; + signal ready_q : std_logic; + +begin + + ----------------------------------------------------------------------------- + -- Process seq + -- + -- Purpose: + -- Implements the sequential elements. + -- + seq: process (clock_i, res_n_i) + begin + if res_n_i = '0' then + reg_q <= (others => '0'); + we_q <= false; + ready_q <= '0'; + + elsif clock_i'event and clock_i = '1' then + -- READY Flag Output ---------------------------------------------------- + if ready_q = '0' and we_q then + if clk_en_i then + -- assert READY when write access happened + ready_q <= '1'; + end if; + elsif ce_n_i = '1' then + -- deassert READY when access has finished + ready_q <= '0'; + end if; + + -- Register Selection --------------------------------------------------- + if ce_n_i = '0' and we_n_i = '0' then + if clk_en_i then + if d_i(0) = '1' then + reg_q <= d_i(1 to 3); + end if; + we_q <= true; + end if; + else + we_q <= false; + end if; + + end if; + end process seq; + -- + ----------------------------------------------------------------------------- + + + ----------------------------------------------------------------------------- + -- Output mapping + ----------------------------------------------------------------------------- + tone1_we_o <= reg_q(0 to 1) = "00" and we_q; + tone2_we_o <= reg_q(0 to 1) = "01" and we_q; + tone3_we_o <= reg_q(0 to 1) = "10" and we_q; + noise_we_o <= reg_q(0 to 1) = "11" and we_q; + + r2_o <= reg_q(2); + + ready_o <= ready_q + when ce_n_i = '0' else + '1'; + +end rtl; |