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// $Id: //acds/rel/13.0sp1/ip/merlin/altera_reset_controller/altera_reset_synchronizer.v#1 $
// $Revision: #1 $
// $Date: 2013/03/07 $
// $Author: swbranch $
// -----------------------------------------------
// Reset Synchronizer
// -----------------------------------------------
`timescale 1 ns / 1 ns
module altera_reset_synchronizer
#(
parameter ASYNC_RESET = 1,
parameter DEPTH = 2
)
(
input reset_in /* synthesis ALTERA_ATTRIBUTE = "SUPPRESS_DA_RULE_INTERNAL=R101" */,
input clk,
output reset_out
);
// -----------------------------------------------
// Synchronizer register chain. We cannot reuse the
// standard synchronizer in this implementation
// because our timing constraints are different.
//
// Instead of cutting the timing path to the d-input
// on the first flop we need to cut the aclr input.
//
// We omit the "preserve" attribute on the final
// output register, so that the synthesis tool can
// duplicate it where needed.
// -----------------------------------------------
(*preserve*) reg [DEPTH-1:0] altera_reset_synchronizer_int_chain;
reg altera_reset_synchronizer_int_chain_out;
generate if (ASYNC_RESET) begin
// -----------------------------------------------
// Assert asynchronously, deassert synchronously.
// -----------------------------------------------
always @(posedge clk or posedge reset_in) begin
if (reset_in) begin
altera_reset_synchronizer_int_chain <= {DEPTH{1'b1}};
altera_reset_synchronizer_int_chain_out <= 1'b1;
end
else begin
altera_reset_synchronizer_int_chain[DEPTH-2:0] <= altera_reset_synchronizer_int_chain[DEPTH-1:1];
altera_reset_synchronizer_int_chain[DEPTH-1] <= 0;
altera_reset_synchronizer_int_chain_out <= altera_reset_synchronizer_int_chain[0];
end
end
assign reset_out = altera_reset_synchronizer_int_chain_out;
end else begin
// -----------------------------------------------
// Assert synchronously, deassert synchronously.
// -----------------------------------------------
always @(posedge clk) begin
altera_reset_synchronizer_int_chain[DEPTH-2:0] <= altera_reset_synchronizer_int_chain[DEPTH-1:1];
altera_reset_synchronizer_int_chain[DEPTH-1] <= reset_in;
altera_reset_synchronizer_int_chain_out <= altera_reset_synchronizer_int_chain[0];
end
assign reset_out = altera_reset_synchronizer_int_chain_out;
end
endgenerate
endmodule
