Add icestick "checker" example

4 files changed, 108 insertions, 3 deletions

diff --git a/examples/icestick/.gitignore b/examples/icestick/.gitignore
index bb30525..c854ccc 100644
--- a/examples/icestick/.gitignore
+++ b/examples/icestick/.gitignore
@@ -11,3 +11,12 @@ rs232demo_tb.vcd
 rs232demo_syn.v
 rs232demo_syntb
 rs232demo_syntb.vcd
+checker.bin
+checker.blif
+checker.asc
+checker.rpt
+checker_tb
+checker_tb.vcd
+checker_syn.v
+checker_syntb
+checker_syntb.vcd
diff --git a/examples/icestick/Makefile b/examples/icestick/Makefile
index d687d14..8b8e741 100644
--- a/examples/icestick/Makefile
+++ b/examples/icestick/Makefile
@@ -1,5 +1,6 @@
 PROJ = example
 # PROJ = rs232demo
+# PROJ = checker
 
 PIN_DEF = icestick.pcf
 DEVICE = hx1k
@@ -22,16 +23,16 @@ all: $(PROJ).rpt $(PROJ).bin
 	iverilog -o $@ $^
 
 %_tb.vcd: %_tb
-	./$< +vcd=$@
+	vvp -N $< +vcd=$@
 
 %_syn.v: %.blif
-	yosys -o $@ $^
+	yosys -p 'read_blif -wideports $^; write_verilog $@'
 
 %_syntb: %_tb.v %_syn.v
 	iverilog -o $@ $^ `yosys-config --datdir/ice40/cells_sim.v`
 
 %_syntb.vcd: %_syntb
-	./$< +vcd=$@
+	vvp -N $< +vcd=$@
 
 prog: $(PROJ).bin
 	iceprog $<
diff --git a/examples/icestick/checker.v b/examples/icestick/checker.v
new file mode 100644
index 0000000..63c70fe
--- /dev/null
+++ b/examples/icestick/checker.v
@@ -0,0 +1,55 @@
+// A simple circuit that can be used to detect brownouts and other hardware issues
+
+module top (
+	input clk,
+	output LED1,
+	output LED2,
+	output LED3,
+	output LED4,
+	output LED5
+);
+	reg [7:0] reset_counter = 0;
+	reg resetn = 0;
+
+	always @(posedge clk) begin
+		reset_counter <= reset_counter + 1;
+		resetn <= resetn | &reset_counter;
+	end
+
+	reg error, rdmode, rdfin;
+
+	reg [31:0] scratchpad [0:1023];
+	reg [31:0] xorshift32_state;
+	reg [9:0] index;
+
+	reg [31:0] next_xorshift32_state;
+
+	always @* begin
+		next_xorshift32_state =      xorshift32_state ^ (     xorshift32_state << 13);
+		next_xorshift32_state = next_xorshift32_state ^ (next_xorshift32_state >> 17);
+		next_xorshift32_state = next_xorshift32_state ^ (next_xorshift32_state <<  5);
+	end
+
+	always @(posedge clk) begin
+		xorshift32_state <= &index ? 123456789 : next_xorshift32_state;
+		index <= index + 1;
+
+		if (!resetn) begin
+			xorshift32_state <= 123456789;
+			index <= 0;
+			error <= 0;
+			rdmode <= 0;
+			rdfin <= 0;
+		end else
+		if (!rdmode) begin
+			scratchpad[index] <= xorshift32_state;
+			rdmode <= &index;
+		end else begin
+			if (scratchpad[index] != xorshift32_state) error <= 1;
+			rdfin <= rdfin || &index;
+		end
+	end
+
+	wire ok = resetn && rdfin && !error;
+	assign LED1 = error, LED2 = error, LED3 = error, LED4 = error, LED5 = ok;
+endmodule
diff --git a/examples/icestick/checker_tb.v b/examples/icestick/checker_tb.v
new file mode 100644
index 0000000..241c89e
--- /dev/null
+++ b/examples/icestick/checker_tb.v
@@ -0,0 +1,40 @@
+module testbench;
+	reg clk;
+	always #5 clk = (clk === 1'b0);
+
+	wire ok;
+
+	top uut (
+		.clk(clk),
+		.LED5(ok)
+	);
+
+	reg [4095:0] vcdfile;
+
+	initial begin
+		if ($value$plusargs("vcd=%s", vcdfile)) begin
+			$dumpfile(vcdfile);
+			$dumpvars(0, testbench);
+		end
+	end
+
+	initial begin
+		@(posedge ok);
+		@(negedge ok);
+		$display("ERROR: detected falling edge on OK pin!");
+		$stop;
+	end
+
+	initial begin
+		repeat (3000) @(posedge clk);
+
+		if (!ok) begin
+			$display("ERROR: OK pin not asserted after 3000 cycles!");
+			$stop;
+		end
+
+		repeat (10000) @(posedge clk);
+		$display("SUCCESS: OK pin still asserted after 10000 cycles.");
+		$finish;
+	end
+endmodule