Add icestick "checker" example

1 files changed, 55 insertions, 0 deletions

diff --git a/examples/icestick/checker.v b/examples/icestick/checker.v
new file mode 100644
index 0000000..63c70fe
--- /dev/null
+++ b/examples/icestick/checker.v
@@ -0,0 +1,55 @@
+// 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 = error, LED2 = error, LED3 = error, LED4 = error, LED5 = ok;
+endmodule