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// A simple circuit that can be used to detect brownouts and other hardware issues
module top (
input clk,
output LED1,
output LED2,
output LED3,
output LED4,
output LED5
);
reg [7:0] reset_counter = 0;
reg resetn = 0;
always @(posedge clk) begin
reset_counter <= reset_counter + 1;
resetn <= resetn | &reset_counter;
end
reg error, rdmode, rdfin;
reg [31:0] scratchpad [0:1023];
reg [31:0] xorshift32_state;
reg [9:0] index;
reg [31:0] next_xorshift32_state;
always @* begin
next_xorshift32_state = xorshift32_state ^ ( xorshift32_state << 13);
next_xorshift32_state = next_xorshift32_state ^ (next_xorshift32_state >> 17);
next_xorshift32_state = next_xorshift32_state ^ (next_xorshift32_state << 5);
end
always @(posedge clk) begin
xorshift32_state <= &index ? 123456789 : next_xorshift32_state;
index <= index + 1;
if (!resetn) begin
xorshift32_state <= 123456789;
index <= 0;
error <= 0;
rdmode <= 0;
rdfin <= 0;
end else
if (!rdmode) begin
scratchpad[index] <= xorshift32_state;
rdmode <= &index;
end else begin
if (scratchpad[index] != xorshift32_state) error <= 1;
rdfin <= rdfin || &index;
end
end
wire ok = resetn && rdfin && !error;
assign LED1 = 0, LED2 = error, LED3 = 0, LED4 = error, LED5 = ok;
endmodule
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