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//----------------------------------------------------------------------------
// Copyright (C) 2009 , Olivier Girard
//
// Redistribution and use in source and binary 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 binary 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 authors nor the names of its 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 COPYRIGHT HOLDER 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
//
//----------------------------------------------------------------------------
//
// *File Name: omsp_clock_mux.v
//
// *Module Description:
// Standard clock mux for the openMSP430
//
// *Author(s):
// - Olivier Girard, olgirard@gmail.com
//
//----------------------------------------------------------------------------
// $Rev: 103 $
// $LastChangedBy: olivier.girard $
// $LastChangedDate: 2011-03-05 15:44:48 +0100 (Sat, 05 Mar 2011) $
//----------------------------------------------------------------------------
module omsp_clock_mux (
// OUTPUTs
clk_out, // Clock output
// INPUTs
clk_in0, // Clock input 0
clk_in1, // Clock input 1
reset, // Reset
scan_mode, // Scan mode (clk_in0 is selected in scan mode)
select // Clock selection
);
// OUTPUTs
//=========
output clk_out; // Clock output
// INPUTs
//=========
input clk_in0; // Clock input 0
input clk_in1; // Clock input 1
input reset; // Reset
input scan_mode; // Scan mode (clk_in0 is selected in scan mode)
input select; // Clock selection
//===========================================================================================================================//
// 1) CLOCK MUX //
//===========================================================================================================================//
// //
// The following (glitch free) clock mux is implemented as following: //
// //
// //
// //
// //
// +-----. +--------+ +--------+ //
// select >>----+-------------O| \ | | | | +-----. //
// | | |---| D Q |---| D Q |--+-------| \ //
// | +-------O| / | | | | | | |O-+ //
// | | +-----' | | | | | +--O| / | //
// | | | /\ | | /\ | | | +-----' | //
// | | +--+--+--+ +--+--+--+ | | | //
// | | O | | | | //
// | | | | | | | +-----. //
// clk_in0 >>----------------------------------+------------+-----------+ +--| \ //
// | | | | |----<< clk_out //
// | | +---------------------------------------+ +--| / //
// | | | | +-----' //
// | +---------------------------------------------+ | //
// | | | | //
// | | +-----. +--------+ +--------+ | | //
// | +-O| \ | | | | | +-----. | //
// | | |---| D Q |---| D Q |--+-------| \ | //
// +--------------| / | | | | | |O-+ //
// +-----' | | | | +--O| / //
// | /\ | | /\ | | +-----' //
// +--+--+--+ +--+--+--+ | //
// O | | //
// | | | //
// clk_in1 >>----------------------------------+------------+-----------+ //
// //
// //
//===========================================================================================================================//
//-----------------------------------------------------------------------------
// Wire declarations
//-----------------------------------------------------------------------------
wire in0_select;
reg in0_select_s;
reg in0_select_ss;
wire in0_enable;
wire in1_select;
reg in1_select_s;
reg in1_select_ss;
wire in1_enable;
wire clk_in0_inv;
wire clk_in1_inv;
wire gated_clk_in0;
wire gated_clk_in1;
//-----------------------------------------------------------------------------
// CLK_IN0 Selection
//-----------------------------------------------------------------------------
assign in0_select = ~select & ~in1_select_ss;
always @ (posedge clk_in0_inv or posedge reset)
if (reset) in0_select_s <= 1'b1;
else in0_select_s <= in0_select;
always @ (posedge clk_in0 or posedge reset)
if (reset) in0_select_ss <= 1'b1;
else in0_select_ss <= in0_select_s;
assign in0_enable = in0_select_ss | scan_mode;
//-----------------------------------------------------------------------------
// CLK_IN1 Selection
//-----------------------------------------------------------------------------
assign in1_select = select & ~in0_select_ss;
always @ (posedge clk_in1_inv or posedge reset)
if (reset) in1_select_s <= 1'b0;
else in1_select_s <= in1_select;
always @ (posedge clk_in1 or posedge reset)
if (reset) in1_select_ss <= 1'b0;
else in1_select_ss <= in1_select_s;
assign in1_enable = in1_select_ss & ~scan_mode;
//-----------------------------------------------------------------------------
// Clock MUX
//-----------------------------------------------------------------------------
//
// IMPORTANT NOTE:
// Because the clock network is a critical part of the design,
// the following combinatorial logic should be replaced with
// direct instanciation of standard cells from target library.
// Don't forget the "dont_touch" attribute to make sure
// synthesis won't mess it up.
//
// Replace with standard cell INVERTER
assign clk_in0_inv = ~clk_in0;
assign clk_in1_inv = ~clk_in1;
// Replace with standard cell NAND2
assign gated_clk_in0 = ~(clk_in0_inv & in0_enable);
assign gated_clk_in1 = ~(clk_in1_inv & in1_enable);
// Replace with standard cell AND2
assign clk_out = (gated_clk_in0 & gated_clk_in1);
endmodule // omsp_clock_gate
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