1 files changed, 77 insertions, 52 deletions

diff --git a/fpga/usrp3/top/x300/gen_ddrlvds.v b/fpga/usrp3/top/x300/gen_ddrlvds.v
index 680b10c84..7b0e4a6a1 100644
--- a/fpga/usrp3/top/x300/gen_ddrlvds.v
+++ b/fpga/usrp3/top/x300/gen_ddrlvds.v
@@ -1,7 +1,6 @@
 
 
-module gen_ddrlvds
-  (
+module gen_ddrlvds (
    // 2X Radio clock
    input tx_clk_2x,
    // 1X Radio Clock
@@ -23,76 +22,102 @@ module gen_ddrlvds
    input [15:0] q,
    // Rising edge sampled on sync_dacs triggers frame sync sequence
    input sync_dacs
-   );
-
-   reg [15:0] 	i_reg, q_reg;
-   reg [15:0] 	i_2x, q_2x;
-   reg 		phase, phase_2x;
-   reg 		rising_edge;
-   wire [15:0] 	i_and_q_2x;
-   reg 		sync_2x;
-   reg 		sync_dacs_reg;
-   
-   
-   
-   genvar 	z;
-   wire [7:0] 	tx_int;
-   wire 	tx_clk_2x_int;
-   wire 	tx_frame_int;
-   
-   (* keep = "true", max_fanout = 10 *) wire phase_eq_phase2x = (phase == phase_2x);
+);
 
+   localparam SYNC_PULSE_WIDTH = 3'd2;
+
+   //
+   // Figure out the 1X clock level
+   //
+   localparam TX_CLK_1X_LOW   = 1'b0;
+   localparam TX_CLK_1X_HIGH  = 1'b1;
+
+   reg   tx_clk_1x_level;
+   reg   phase, phase_2x;
+   reg   reset_2x;
 
    always @(posedge tx_clk_1x)
-     if (reset)
-       phase <= 1'b0;
-     else
-       phase <= ~phase;
+      if (reset)
+         phase <= 1'b0;
+      else
+         phase <= ~phase;
 
+   always @(posedge tx_clk_2x)
+   begin
+      phase_2x <= phase;
+      //Pipeline reset and tx_clk_1x_level
+      reset_2x <= reset;
+      tx_clk_1x_level <= (phase == phase_2x) ? TX_CLK_1X_HIGH : TX_CLK_1X_LOW;
+   end
 
    //
    // Pipeline input data so that 1x to 2x clock domain jump includes no logic external to this module.
    //
+   reg [15:0]  i_reg, q_reg;
+   reg         sync_dacs_reg;
+
    always @(posedge tx_clk_1x) 
-     begin
-	i_reg <= i;
-	q_reg <= q;
-	sync_dacs_reg <= sync_dacs;
-     end  
+   begin
+      i_reg <= i;
+      q_reg <= q;
+      sync_dacs_reg <= sync_dacs;
+   end  
+
+   //
+   // Generate frame signal and interleave I and Q signals
+   //
+   reg [15:0]  i_2x, q_2x;
+   reg [2:0]   sync_count;
+   reg         frame;
 
    always @(posedge tx_clk_2x)
-     begin
-	// Move 1x data to 2x domain, mostly just to add pipeline regs
-	// for timing closure.
-	i_2x <= i_reg;
-	q_2x <= q_reg;
-	// Sample phase to determine when 1x clock edges occur.
-	// To sync multiple AD9146 DAC's an extended assertion of FRAME is required,
-	// when sync flag set, squash one rising_edge assertion which causes a 3 word assertion of FRAME,
-	// also reset sync flag. "sync_dacs" comes from 1x clk and pulse lasts 2 2x clock cycles...this is accounted for.
-	sync_2x <=  (phase_eq_phase2x && sync_2x) ? 1'b0 /*RESET */ : (sync_dacs_reg) ? 1'b1 /* SET */ : sync_2x /* HOLD */;
-	rising_edge <= (phase_eq_phase2x && ~sync_2x);
-	phase_2x <= phase;
-     end
-
-   // Interleave I and Q as SDR signals
-   assign i_and_q_2x = rising_edge ? q_2x : i_2x;
+   begin
+      // Move 1x data to 2x domain, mostly just to add pipeline regs
+      // for timing closure.
+      i_2x <= i_reg;
+      q_2x <= q_reg;
+      
+      // Sample phase to determine when 1x clock edges occur.
+      // To sync multiple AD9146 DAC's an extended assertion of FRAME is required,
+      // when sync flag set, squash one frame assertion which causes a SYNC_PULSE_WIDTH+1 word assertion of FRAME,
+      // also reset sync flag. "sync_dacs" comes from 1x clk and pulse lasts 2 2x clock cycles...this is accounted for.
+      if (reset_2x) begin
+         frame <= 0;
+         sync_count <= 3'd0;
+      end else begin
+         frame <= (tx_clk_1x_level == TX_CLK_1X_LOW) | (sync_count != 3'd0);
+         if ((tx_clk_1x_level == TX_CLK_1X_LOW) & sync_dacs_reg)
+            sync_count <= SYNC_PULSE_WIDTH;
+         else if (sync_count > 3'd0)
+            sync_count <= sync_count - 3'd1;
+      end
+   end
+
+   wire [15:0] i_and_q_2x = frame ? i_2x : q_2x;
    
+   //
+   // Instantiate IO primitives for the source synchronous interface
+   //
+   wire [7:0]  tx_int;
+   wire        tx_clk_2x_int;
+   wire        tx_frame_int;
+
+   genvar z;
    generate	
       for(z = 0; z < 8; z = z + 1)
-	begin : gen_pins
-	   OBUFDS obufds (.I(tx_int[z]), .O(tx_d_p[z]), .OB(tx_d_n[z]));
-	   ODDR #(.DDR_CLK_EDGE("SAME_EDGE")) oddr
-	     (.Q(tx_int[z]), .C(tx_clk_2x),
-	      .CE(1'b1), .D1(i_and_q_2x[z+8]), .D2(i_and_q_2x[z]), .S(1'b0), .R(1'b0));
-	end
+      begin : gen_pins
+         OBUFDS obufds (.I(tx_int[z]), .O(tx_d_p[z]), .OB(tx_d_n[z]));
+         ODDR #(.DDR_CLK_EDGE("SAME_EDGE")) oddr
+           (.Q(tx_int[z]), .C(tx_clk_2x),
+            .CE(1'b1), .D1(i_and_q_2x[z+8]), .D2(i_and_q_2x[z]), .S(1'b0), .R(1'b0));
+      end
    endgenerate
 
    // Generate framing signal to identify I and Q
    OBUFDS obufds_frame (.I(tx_frame_int), .O(tx_frame_p), .OB(tx_frame_n));
    ODDR #(.DDR_CLK_EDGE("SAME_EDGE")) oddr_frame
      (.Q(tx_frame_int), .C(tx_clk_2x),
-      .CE(1'b1), .D1(~rising_edge), .D2(~rising_edge), .S(1'b0), .R(1'b0));
+      .CE(1'b1), .D1(frame), .D2(frame), .S(1'b0), .R(1'b0));
 
    // Source synchronous clk
    OBUFDS obufds_clk (.I(tx_clk_2x_int), .O(tx_clk_2x_p), .OB(tx_clk_2x_n));