Add cordic.sv and test_saw2sin.py

test_saw2sin.py: cocotb testbench using verilator
cordic.sv: o_sin adjustments mask erratic results at extremes, avg error is 1.346 vs testbench

Makefile

@@ -0,0 +1,9 @@
+SIM ?= verilator
+TOPLEVEL_LANG ?= verilog
+VERILOG_SOURCES += $(PWD)/saw2sin.sv $(PWD)/cordic.sv
+TOPLEVEL = saw2sin
+MODULE = test_saw2sin
+EXTRA_ARGS += --trace-fst --trace-structs
+
+# include cocotb's make rules to take care of the simulator setup
+include $(shell cocotb-config --makefiles)/Makefile.sim

cordic.sv

@@ -0,0 +1,69 @@
+`default_nettype none
+
+module cordic
+( input  var [15:0] i_qph // 16-bit unsigned, representing 0-90 degrees
+, output var [15:0] o_sin // 16-bit unsigned, representing 0-1
+);
+
+// Gain is 1.164435, 2^16 / 1.164435 = 56281.37... = 0xDBD9
+logic [15:0] i_x;
+logic [15:0] i_y;
+always_comb i_x = i_qph[15] ? 16'h0000 : 16'hDBD9;
+always_comb i_y = i_qph[15] ? 16'hDBD9 : 16'h0000;
+
+// Cordic angle table
+logic [22:0] cordic_angle [0:18];
+always_comb cordic_angle[ 0] = 23'h25C80A; // 26.565051 degrees
+always_comb cordic_angle[ 1] = 23'h13F670; // 14.036243 degrees
+always_comb cordic_angle[ 2] = 23'h0A2223; //  7.125016 degrees
+always_comb cordic_angle[ 3] = 23'h05161A; //  3.576334 degrees
+always_comb cordic_angle[ 4] = 23'h028BAF; //  1.789911 degrees
+always_comb cordic_angle[ 5] = 23'h0145EC; //  0.895174 degrees
+always_comb cordic_angle[ 6] = 23'h00A2F8; //  0.447614 degrees
+always_comb cordic_angle[ 7] = 23'h00517C; //  0.223811 degrees
+always_comb cordic_angle[ 8] = 23'h0028BE; //  0.111906 degrees
+always_comb cordic_angle[ 9] = 23'h00145F; //  0.055953 degrees
+always_comb cordic_angle[10] = 23'h000A2F; //  0.027976 degrees
+always_comb cordic_angle[11] = 23'h000517; //  0.013988 degrees
+always_comb cordic_angle[12] = 23'h00028B; //  0.006994 degrees
+always_comb cordic_angle[13] = 23'h000145; //  0.003497 degrees
+always_comb cordic_angle[14] = 23'h0000A2; //  0.001749 degrees
+always_comb cordic_angle[15] = 23'h000051; //  0.000874 degrees
+always_comb cordic_angle[16] = 23'h000028; //  0.000437 degrees
+always_comb cordic_angle[17] = 23'h000014; //  0.000219 degrees
+always_comb cordic_angle[18] = 23'h00000A; //  0.000109 degrees
+
+/* verilator lint_off UNOPTFLAT */
+logic [18:0] x [0:19];
+logic [18:0] y [0:19];
+logic [22:0] p [0:19];
+/* verilator lint_on UNOPTFLAT */
+
+// Extend input from input to working widths
+always_comb x[0] = {1'b0, i_x, {2{1'b0}}};
+always_comb y[0] = {1'b0, i_y, {2{1'b0}}};
+always_comb p[0] = {i_qph, {7{1'b0}}};
+  // Max pos = 23'h3FFF80, Max neg = 23'h400000
+
+/* verilator lint_off ALWCOMBORDER */
+for (genvar i = 0; i < 19; i = i + 1) begin: l_cordic_steps
+  // If phase is negative, rotate CW, otherwise CCW
+  always_comb
+    if (p[i][22]) begin
+      x[i+1] = x[i] + (y[i] >>> (i+1));
+      y[i+1] = y[i] - (x[i] >>> (i+1));
+      p[i+1] = p[i] + cordic_angle[i];
+    end else begin
+      x[i+1] = x[i] - (y[i] >>> (i+1));
+      y[i+1] = y[i] + (x[i] >>> (i+1));
+      p[i+1] = p[i] - cordic_angle[i];
+    end
+end
+/* verilator lint_on ALWCOMBORDER */
+
+always_comb
+  if (i_qph > 16'd65508)   o_sin = 16'hFFFF;
+  else if (i_qph < 16'd32) o_sin = i_qph + (i_qph >> 1);
+  else                     o_sin = y[19][17:2];
+
+endmodule

test_saw2sin.py

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+import cocotb
+from cocotb.triggers import Timer
+from math import sin, cos, pi
+
+@cocotb.test()
+async def test_new_cordic(dut):
+    """Test that cordic matches sin"""
+
+    diff = 0
+    for cycle in range(0, 65536):
+        dut.i_saw.value = cycle
+        await Timer(1, units='ps')
+        e_sin = 32768 * (sin((cycle * pi) / (2**15)) + 1)
+        error = e_sin - dut.o_sin.value
+        if abs(error) > 4:
+            dut._log.info("cycle %d: expected %d, got %d, error %d"
+                % (cycle, e_sin, dut.o_sin.value, error))
+        diff += abs(error)
+
+    dut._log.info("Testbench finished, average error %f" % (diff / 65536))