From 4b57bdfa8074511f3cd97b617572c96d679369b4 Mon Sep 17 00:00:00 2001
From: Aadi Desai <21363892+supleed2@users.noreply.github.com>
Date: Sun, 4 Jun 2023 12:05:45 +0100
Subject: [PATCH] Update `cordic.sv` and `saw2sin.sv` for better accuracy,
 `genSaw.sv` to fix polarity of tri/sin

---
 rtl/cordic.sv  | 19 +++++++++++++++----
 rtl/genSaw.sv  |  4 ++--
 rtl/saw2sin.sv | 15 ++++++++++-----
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/rtl/cordic.sv b/rtl/cordic.sv
index 3eb7f53..1c39097 100644
--- a/rtl/cordic.sv
+++ b/rtl/cordic.sv
@@ -33,9 +33,11 @@ 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}}};
@@ -43,15 +45,24 @@ 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 x[i+1] = (p[i][22]) ? x[i] + (y[i] >>> (i+1)) : x[i] - (y[i] >>> (i+1));
-  always_comb y[i+1] = (p[i][22]) ? y[i] - (x[i] >>> (i+1)) : y[i] + (x[i] >>> (i+1));
-  always_comb p[i+1] = (p[i][22]) ? p[i] + cordic_angle[i] : p[i] - cordic_angle[i];
+  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;
+  if (i_qph > 16'd65508)   o_sin = 16'hFFFE;
   else if (i_qph < 16'd32) o_sin = i_qph + (i_qph >> 1);
   else                     o_sin = y[19][17:2];
 
diff --git a/rtl/genSaw.sv b/rtl/genSaw.sv
index 69948ee..ee025e5 100644
--- a/rtl/genSaw.sv
+++ b/rtl/genSaw.sv
@@ -54,8 +54,8 @@ always_comb // Select output waveform
   case (i_wave[1:0])
     2'd0: o_sample = saw;
     2'd1: o_sample = square;
-    2'd2: o_sample = triangle;
-    2'd3: o_sample = sine;
+    2'd2: o_sample = {~triangle[15], triangle[14:0]};
+    2'd3: o_sample = {~sine[15], sine[14:0]};
   endcase
 
 endmodule
diff --git a/rtl/saw2sin.sv b/rtl/saw2sin.sv
index f3aee26..c74347d 100644
--- a/rtl/saw2sin.sv
+++ b/rtl/saw2sin.sv
@@ -13,8 +13,8 @@ always_comb reverse = i_saw[14];
 
 logic [15:0] qsaw;
 always_comb qsaw = reverse
-  ? {~i_saw[13:0], 2'b01} // Reverse
-  : {i_saw[13:0], 2'b00}; // Normal
+  ? {~i_saw[13:0], 2'b11} // Reverse
+  : {i_saw[13:0], 2'b01}; // Normal
 
 logic [15:0] qsin;
 cordic cordic
@@ -22,8 +22,13 @@ cordic cordic
 , .o_sin (qsin)
 );
 
-always_comb o_sin = invert
-  ? ~{1'b1, qsin[15:1]} + 1 // Invert
-  : {1'b1, qsin[15:1]};     // Normal
+logic [16:0] sin;
+always_comb sin = reverse
+  ? (invert ? ~{1'b1, qsin[15:0]}          // Reverse, Invert
+            : {1'b1, qsin[15:0]} + 17'd1)  // Reverse, Normal
+  : (invert ? ~{1'b1, qsin[15:0]} + 17'd2  // Normal, Invert
+            : {1'b1, qsin[15:0]} + 17'd0); // Normal, Normal
+
+always_comb o_sin = sin[16:1];
 
 endmodule