Merge branch 'fpga_master' into uhd_next

11 files changed, 445 insertions, 13 deletions

diff --git a/fpga/usrp2/sdr_lib/Makefile.srcs b/fpga/usrp2/sdr_lib/Makefile.srcs
index defbced17..629b92cc8 100644
--- a/fpga/usrp2/sdr_lib/Makefile.srcs
+++ b/fpga/usrp2/sdr_lib/Makefile.srcs
@@ -25,8 +25,11 @@ cordic_z24.v \
 cordic_stage.v \
 dsp_core_rx.v \
 dsp_core_tx.v \
+dspengine_16to8.v \
 hb_dec.v \
 hb_interp.v \
+pipectrl.v \
+pipestage.v \
 round.v \
 round_reg.v \
 round_sd.v \
diff --git a/fpga/usrp2/sdr_lib/clip_reg.v b/fpga/usrp2/sdr_lib/clip_reg.v
index d5e98d982..9098fd5b8 100644
--- a/fpga/usrp2/sdr_lib/clip_reg.v
+++ b/fpga/usrp2/sdr_lib/clip_reg.v
@@ -23,16 +23,24 @@
 
 module clip_reg
   #(parameter bits_in=0,
-    parameter bits_out=0)
+    parameter bits_out=0,
+    parameter STROBED=1'b0)
     (input clk,
      input [bits_in-1:0] in,
-     output reg [bits_out-1:0] out);
+     output reg [bits_out-1:0] out,
+     input strobe_in,
+     output reg strobe_out);
    
    wire [bits_out-1:0] temp;
 
    clip #(.bits_in(bits_in),.bits_out(bits_out)) clip (.in(in),.out(temp));
+
+   always @(posedge clk)
+     strobe_out <= strobe_in;
+   
    always @(posedge clk)
-     out <= temp;
+     if(strobe_in | ~STROBED)
+       out <= temp;
    
 endmodule // clip_reg
 
diff --git a/fpga/usrp2/sdr_lib/dsp_core_rx.v b/fpga/usrp2/sdr_lib/dsp_core_rx.v
index 639744de7..d1c7e238a 100644
--- a/fpga/usrp2/sdr_lib/dsp_core_rx.v
+++ b/fpga/usrp2/sdr_lib/dsp_core_rx.v
@@ -94,8 +94,10 @@ module dsp_core_rx
 	    .xi({adc_i_mux[23],adc_i_mux}),. yi({adc_q_mux[23],adc_q_mux}), .zi(phase[31:8]),
 	    .xo(i_cordic),.yo(q_cordic),.zo() );
 
-   clip_reg #(.bits_in(25), .bits_out(24)) clip_i (.clk(clk), .in(i_cordic), .out(i_cordic_clip));
-   clip_reg #(.bits_in(25), .bits_out(24)) clip_q (.clk(clk), .in(q_cordic), .out(q_cordic_clip));
+   clip_reg #(.bits_in(25), .bits_out(24)) clip_i
+     (.clk(clk), .in(i_cordic), .strobe_in(1'b1), .out(i_cordic_clip));
+   clip_reg #(.bits_in(25), .bits_out(24)) clip_q
+     (.clk(clk), .in(q_cordic), .strobe_in(1'b1), .out(q_cordic_clip));
 
    // CIC decimator  24 bit I/O
    cic_strober cic_strober(.clock(clk),.reset(rst),.enable(run),.rate(cic_decim_rate),
diff --git a/fpga/usrp2/sdr_lib/dspengine_16to8.v b/fpga/usrp2/sdr_lib/dspengine_16to8.v
new file mode 100644
index 000000000..53c5d29da
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/dspengine_16to8.v
@@ -0,0 +1,221 @@
+
+// Copyright 2011 Ettus Research LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+module dspengine_16to8
+  #(parameter BASE = 0,
+    parameter BUF_SIZE = 9)
+   (input clk, input reset, input clear,
+    input set_stb, input [7:0] set_addr, input [31:0] set_data,
+
+    output access_we,
+    output access_stb,
+    input access_ok,
+    output access_done,
+    output access_skip_read,
+    output [BUF_SIZE-1:0] access_adr,
+    input [BUF_SIZE-1:0] access_len,
+    output [35:0] access_dat_o,
+    input [35:0] access_dat_i
+    );
+
+   wire 	 convert;
+   wire [17:0] 	 scale_factor;
+   
+   setting_reg #(.my_addr(BASE),.width(19)) sr_16to8
+     (.clk(clk),.rst(reset),.strobe(set_stb),.addr(set_addr),
+      .in(set_data),.out({convert,scale_factor}),.changed());
+   
+   reg [2:0] 	 dsp_state;
+   localparam DSP_IDLE = 0;
+   localparam DSP_PARSE_HEADER = 1;
+   localparam DSP_CONVERT = 2;
+   localparam DSP_CONVERT_DRAIN_PIPE = 3;
+   localparam DSP_READ_TRAILER = 4;
+   localparam DSP_WRITE_TRAILER = 5;
+   localparam DSP_WRITE_HEADER = 6;
+   localparam DSP_DONE = 7;
+
+   // Parse VITA header
+   wire 	 is_if_data = (access_dat_i[31:29] == 3'b000);
+   wire 	 has_streamid = access_dat_i[28];
+   wire 	 has_classid = access_dat_i[27];
+   wire 	 has_trailer = access_dat_i[26];
+   // 25:24 reserved, aka SOB/EOB
+   wire 	 has_secs = |access_dat_i[23:22];
+   wire 	 has_tics = |access_dat_i[21:20];
+   wire [3:0] 	 hdr_length = 1 + has_streamid + has_classid + has_classid + has_secs + has_tics + has_tics;
+   
+   wire [35:0] 	 prod_i, prod_q;
+   wire [15:0] 	 scaled_i, scaled_q;
+   wire [7:0] 	 i8, q8;
+   reg [7:0] 	 i8_reg, q8_reg;
+   wire 	 stb_read, stb_mult, stb_clip, stb_round, val_read, val_mult, val_clip, val_round;
+   wire 	 stb_out, stb_reg;
+   reg 		 even;
+   
+   reg [BUF_SIZE-1:0] read_adr, write_adr;
+   reg 		      has_trailer_reg;
+   
+   wire 	      last = (read_adr + 1) == (access_len - has_trailer_reg);
+   wire 	      last_o, even_o;
+
+   wire 	      stb_write = stb_out & (even_o | last_o);
+   wire 	      send_to_pipe = ~stb_write & (dsp_state == DSP_CONVERT);
+   reg [31:0] 	      new_header, new_trailer, trailer_mask;
+   reg [15:0] 	      length;
+   reg 		      wait_for_trailer;
+   
+   always @(posedge clk)
+     if(reset | clear)
+       dsp_state <= DSP_IDLE;
+     else
+       case(dsp_state)
+	 DSP_IDLE :
+	   begin
+	      read_adr <= 0;
+	      write_adr <= 0;
+	      even <= 0;
+	      if(access_ok)
+		dsp_state <= DSP_PARSE_HEADER;
+	   end
+	 
+	 DSP_PARSE_HEADER :
+	   begin
+	      has_trailer_reg <= has_trailer;
+	      new_header[31:16] <= access_dat_i[31:16];
+	      new_header[15:0] <= access_len;
+	      length <= access_len;
+	      if(is_if_data & convert)
+		begin
+		   read_adr <= hdr_length;
+		   write_adr <= hdr_length;
+		   dsp_state <= DSP_CONVERT;
+		end
+	      else
+		dsp_state <= DSP_WRITE_HEADER;
+	   end
+	 
+	 DSP_CONVERT:
+	   begin
+	      new_header[26] <= 1'b1;  // all converted packets have a trailer
+	      if(stb_write)
+		write_adr <= write_adr + 1;
+	      else if(stb_read)   // should always be 1 if we are here
+		begin
+		   read_adr <= read_adr + 1;
+		   even <= ~even;
+		   if(last)
+		     begin
+			dsp_state <= DSP_CONVERT_DRAIN_PIPE;
+			if(~even)
+			  trailer_mask <= 32'h00400400;
+			else
+			  trailer_mask <= 32'h00400000;
+		     end
+		end
+	   end
+	 
+	 DSP_CONVERT_DRAIN_PIPE :
+	   if(stb_write)
+	     begin
+		write_adr <= write_adr + 1;
+		if(last_o)
+		  if(has_trailer_reg)
+		    begin
+		       dsp_state <= DSP_READ_TRAILER;
+		       wait_for_trailer <= 0;
+		    end
+		  else
+		    begin
+		       dsp_state <= DSP_WRITE_TRAILER;
+		       new_trailer <= trailer_mask;
+		    end
+	     end
+
+	 DSP_READ_TRAILER :
+	   begin
+	      wait_for_trailer <= 1;
+	      if(wait_for_trailer)
+		dsp_state <= DSP_WRITE_TRAILER;
+	      new_trailer <= access_dat_i[31:0] | trailer_mask;
+	   end
+
+	 DSP_WRITE_TRAILER :
+	   begin
+	      dsp_state <= DSP_WRITE_HEADER;
+	      write_adr <= 0;
+	      new_header[15:0] <= write_adr + 1;
+	   end
+
+	 DSP_WRITE_HEADER :
+	   dsp_state <= DSP_DONE;
+
+	 DSP_DONE :
+	   begin
+	      read_adr <= 0;
+	      write_adr <= 0;
+	      dsp_state <= DSP_IDLE;
+	   end
+       endcase // case (dsp_state)
+
+   assign access_skip_read = 0;
+   assign access_done = (dsp_state == DSP_DONE);
+
+   assign access_stb = 1;
+
+   assign access_we = (dsp_state == DSP_WRITE_HEADER) | 
+		      (dsp_state == DSP_WRITE_TRAILER) |
+		      stb_write;
+
+   assign access_dat_o = (dsp_state == DSP_WRITE_HEADER) ? { 4'h1, new_header } :
+			 (dsp_state == DSP_WRITE_TRAILER) ? { 4'h2, new_trailer } :
+			 (last_o&~even_o) ? {4'h0, 16'd0, i8, q8 } : 
+			 {4'h0, i8, q8, i8_reg, q8_reg };
+   
+   assign access_adr = (stb_write|(dsp_state == DSP_WRITE_HEADER)|(dsp_state == DSP_WRITE_TRAILER)) ? write_adr : read_adr;
+      
+   // DSP Pipeline
+   
+   wire [15:0] i16 = access_dat_i[31:16];
+   wire [15:0] q16 = access_dat_i[15:0];
+
+   pipectrl #(.STAGES(4), .TAGWIDTH(2)) pipectrl 
+     (.clk(clk), .reset(reset),
+      .src_rdy_i(send_to_pipe), .dst_rdy_o(), // dst_rdy_o will always be 1 since dst_rdy_i is 1, below
+      .src_rdy_o(stb_out), .dst_rdy_i(1),   // always accept output of chain
+      .strobes({stb_round,stb_clip,stb_mult,stb_read}), .valids({val_round,val_clip,val_mult,val_read}),
+      .tag_i({last,even}), .tag_o({last_o,even_o}));
+
+   always @(posedge clk)
+     if(stb_out & ~even_o)
+       {i8_reg,q8_reg} <= {i8,q8};
+   
+   MULT18X18S mult_i 
+     (.P(prod_i), .A(scale_factor), .B({i16,2'b00}), .C(clk), .CE(stb_mult), .R(reset) ); 
+   clip_reg #(.bits_in(24),.bits_out(16),.STROBED(1)) clip_i 
+     (.clk(clk), .in(prod_i[35:12]), .out(scaled_i), .strobe_in(stb_clip), .strobe_out());
+   round_sd #(.WIDTH_IN(16),.WIDTH_OUT(8),.DISABLE_SD(1)) round_i
+     (.clk(clk), .reset(reset), .in(scaled_i), .strobe_in(stb_round), .out(i8), .strobe_out());
+
+   MULT18X18S mult_q 
+     (.P(prod_q), .A(scale_factor), .B({q16,2'b00}), .C(clk), .CE(stb_mult), .R(reset) ); 
+   clip_reg #(.bits_in(24),.bits_out(16),.STROBED(1)) clip_q 
+     (.clk(clk), .in(prod_q[35:12]), .out(scaled_q), .strobe_in(stb_clip), .strobe_out());
+   round_sd #(.WIDTH_IN(16),.WIDTH_OUT(8),.DISABLE_SD(1)) round_q
+     (.clk(clk), .reset(reset), .in(scaled_q), .strobe_in(stb_round), .out(q8), .strobe_out());
+
+endmodule // dspengine_16to8
diff --git a/fpga/usrp2/sdr_lib/pipectrl.v b/fpga/usrp2/sdr_lib/pipectrl.v
new file mode 100644
index 000000000..85d0ce04f
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/pipectrl.v
@@ -0,0 +1,66 @@
+//
+// Copyright 2011 Ettus Research LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+// Control DSP pipeline with 1 cycle per stage.  Minimum 2 stages or this won't work
+module pipectrl
+  #(parameter STAGES = 2, 
+    parameter TAGWIDTH = 1)
+   (input clk,
+    input reset,
+    input src_rdy_i,
+    output dst_rdy_o,
+    output src_rdy_o,
+    input dst_rdy_i,
+    output [STAGES-1:0] strobes,
+    output [STAGES-1:0] valids,
+    input [TAGWIDTH-1:0] tag_i,
+    output [TAGWIDTH-1:0] tag_o);
+
+   wire 		new_input = src_rdy_i & dst_rdy_o;
+   wire 		new_output = src_rdy_o & dst_rdy_i;
+   wire [TAGWIDTH-1:0] 	tags [STAGES-1:0];
+
+   assign dst_rdy_o = ~valids[0] | strobes[1];
+
+   pipestage #(.TAGWIDTH(TAGWIDTH)) head
+     (.clk(clk),.reset(reset), .stb_in(strobes[0]), .stb_out(strobes[1]),.valid(valids[0]),
+      .tag_in(tag_i), .tag_out(tags[0]));
+   assign strobes[0] = src_rdy_i & (~valids[0] | strobes[1]);
+
+   genvar 		i;
+   generate
+      for(i = 1; i < STAGES - 1; i = i + 1)
+	begin : gen_stages
+	   pipestage #(.TAGWIDTH(TAGWIDTH)) pipestage
+	     (.clk(clk),.reset(reset), .stb_in(strobes[i]),.stb_out(strobes[i+1]),.valid(valids[i]),
+	      .tag_in(tags[i-1]),.tag_out(tags[i]));
+	   assign strobes[i] = valids[i-1] & (~valids[i] | strobes[i+1]);
+	end
+   endgenerate
+
+   pipestage #(.TAGWIDTH(TAGWIDTH)) tail
+     (.clk(clk),.reset(reset), .stb_in(strobes[STAGES-1]), .stb_out(dst_rdy_i),.valid(valids[STAGES-1]),
+      .tag_in(tags[STAGES-2]), .tag_out(tags[STAGES-1]));
+   assign strobes[STAGES-1] = valids[STAGES-2] & (~valids[STAGES-1] | new_output);
+   
+   assign src_rdy_o = valids[STAGES-1];
+
+   assign tag_o = tags[STAGES-1];
+   
+endmodule // pipectrl
+
+
diff --git a/fpga/usrp2/sdr_lib/pipestage.v b/fpga/usrp2/sdr_lib/pipestage.v
new file mode 100644
index 000000000..011afb1ba
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/pipestage.v
@@ -0,0 +1,45 @@
+//
+// Copyright 2011 Ettus Research LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+module pipestage
+  #(parameter TAGWIDTH = 1)
+   (input clk,
+    input reset,
+    input stb_in,
+    input stb_out,
+    output reg valid,
+    input [TAGWIDTH-1:0] tag_in,
+    output reg [TAGWIDTH-1:0] tag_out);
+
+   always @(posedge clk)
+     if(reset)
+       begin
+	  valid <= 0;
+	  tag_out <= 0;
+       end
+     else if(stb_in)
+       begin
+	  valid <= 1;
+	  tag_out <= tag_in;
+       end
+     else if(stb_out)
+       begin
+	  valid <= 0;
+	  tag_out <= 0;
+       end
+   
+endmodule // pipestage
diff --git a/fpga/usrp2/sdr_lib/round.v b/fpga/usrp2/sdr_lib/round.v
index 7a137d702..26d5a4cf4 100644
--- a/fpga/usrp2/sdr_lib/round.v
+++ b/fpga/usrp2/sdr_lib/round.v
@@ -2,7 +2,7 @@
 //
 //  USRP - Universal Software Radio Peripheral
 //
-//  Copyright (C) 2007 Matt Ettus
+//  Copyright (C) 2011 Matt Ettus
 //
 //  This program is free software; you can redistribute it and/or modify
 //  it under the terms of the GNU General Public License as published by
@@ -24,12 +24,36 @@
 
 module round
   #(parameter bits_in=0,
-    parameter bits_out=0)
+    parameter bits_out=0,
+    parameter round_to_zero=0,       // original behavior
+    parameter round_to_nearest=1,    // lowest noise
+    parameter trunc=0)               // round to negative infinity
     (input [bits_in-1:0] in,
      output [bits_out-1:0] out,
      output [bits_in-bits_out:0] err);
 
-   assign out = in[bits_in-1:bits_in-bits_out] + (in[bits_in-1] & |in[bits_in-bits_out-1:0]);
+   wire 			 round_corr,round_corr_trunc,round_corr_rtz,round_corr_nearest,round_corr_nearest_safe;
+   
+   assign 			 round_corr_trunc = 0;
+   assign 			 round_corr_rtz = (in[bits_in-1] & |in[bits_in-bits_out-1:0]);
+   assign 			 round_corr_nearest = in[bits_in-bits_out-1];
+
+   generate
+      if(bits_in-bits_out > 1)
+	assign 			 round_corr_nearest_safe = (~in[bits_in-1] & (&in[bits_in-2:bits_out])) ? 0 :
+				 round_corr_nearest;
+      else
+	assign round_corr_nearest_safe = round_corr_nearest;
+   endgenerate
+   
+      
+   assign round_corr = round_to_nearest ? round_corr_nearest_safe :
+		       trunc ? round_corr_trunc : 
+		       round_to_zero ? round_corr_rtz :
+		       0;  // default to trunc
+      
+   assign out = in[bits_in-1:bits_in-bits_out] + round_corr;
+   
    assign err = in - {out,{(bits_in-bits_out){1'b0}}};
    
 endmodule // round
diff --git a/fpga/usrp2/sdr_lib/round_sd.v b/fpga/usrp2/sdr_lib/round_sd.v
index aeeb3502f..94584f6ef 100644
--- a/fpga/usrp2/sdr_lib/round_sd.v
+++ b/fpga/usrp2/sdr_lib/round_sd.v
@@ -2,7 +2,8 @@
 
 module round_sd
   #(parameter WIDTH_IN=18,
-    parameter WIDTH_OUT=16)
+    parameter WIDTH_OUT=16,
+    parameter DISABLE_SD=0)
    (input clk, input reset,
     input [WIDTH_IN-1:0] in, input strobe_in,
     output [WIDTH_OUT-1:0] out, output strobe_out);
@@ -15,7 +16,7 @@ module round_sd
    sign_extend #(.bits_in(ERR_WIDTH),.bits_out(WIDTH_IN)) ext_err (.in(err), .out(err_ext));
    
    add2_and_clip_reg #(.WIDTH(WIDTH_IN)) add2_and_clip_reg
-     (.clk(clk), .rst(reset), .in1(in), .in2(err_ext), .strobe_in(strobe_in), .sum(sum), .strobe_out(strobe_out));
+     (.clk(clk), .rst(reset), .in1(in), .in2((DISABLE_SD == 0) ? err_ext : 0), .strobe_in(strobe_in), .sum(sum), .strobe_out(strobe_out));
    
    round #(.bits_in(WIDTH_IN),.bits_out(WIDTH_OUT)) round_sum (.in(sum), .out(out), .err(err));
    
diff --git a/fpga/usrp2/sdr_lib/round_tb.v b/fpga/usrp2/sdr_lib/round_tb.v
new file mode 100644
index 000000000..ddc464f4a
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/round_tb.v
@@ -0,0 +1,61 @@
+// -*- verilog -*-
+//
+//  USRP - Universal Software Radio Peripheral
+//
+//  Copyright (C) 2011 Matt Ettus
+//
+//  This program is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation; either version 2 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program; if not, write to the Free Software
+//  Foundation, Inc., 51 Franklin Street, Boston, MA  02110-1301  USA
+//
+
+// Rounding "macro"
+// Keeps the topmost bits, does proper 2s comp round to zero (unbiased truncation)
+
+module round_tb();
+
+   localparam IW=8;
+   localparam OW=4;
+   localparam EW=IW-OW+1;
+   
+   reg signed [IW-1:0] in;
+   wire signed [OW-1:0] out;
+   wire signed [EW-1:0] err;
+
+   round #(.bits_in(IW),
+	   .bits_out(OW),
+	   .round_to_zero(0),       // original behavior
+	   .round_to_nearest(1),    // lowest noise
+	   .trunc(0))               // round to negative infinity
+   round (.in(in),.out(out),.err(err));
+
+   initial $dumpfile("round_tb.vcd");
+   initial $dumpvars(0,round_tb);
+
+   wire signed [IW-1:0] out_round = {out,{IW-OW{1'b0}}};
+   
+   initial
+     begin
+	in <= -129;
+	#1;
+	repeat (260)
+	  begin
+	     in <= in + 1;
+	     #1;
+	     $display("In %d, out %d, out_rnd %d, err %d, real err %d",in,out,out_round,-err,out_round-in);
+	     #1;
+	  end
+	$finish;
+     end
+     
+endmodule // round
diff --git a/fpga/usrp2/sdr_lib/rx_dcoffset.v b/fpga/usrp2/sdr_lib/rx_dcoffset.v
index 9840e9e1f..04d7795c0 100644
--- a/fpga/usrp2/sdr_lib/rx_dcoffset.v
+++ b/fpga/usrp2/sdr_lib/rx_dcoffset.v
@@ -42,8 +42,9 @@ module rx_dcoffset
        end
      else if(set_now)
        begin
-	  //integrator <= {set_data[30:0],{(31-int_width){1'b0}}};
 	  fixed <= set_data[31];
+	  if(set_data[30])
+	    integrator <= {set_data[29:0],{(int_width-30){1'b0}}};
        end
      else if(~fixed)
        integrator <= integrator +  {{(alpha_shift){out[WIDTH-1]}},out};
diff --git a/fpga/usrp2/sdr_lib/small_hb_int.v b/fpga/usrp2/sdr_lib/small_hb_int.v
index 387f9e1cb..b69c45413 100644
--- a/fpga/usrp2/sdr_lib/small_hb_int.v
+++ b/fpga/usrp2/sdr_lib/small_hb_int.v
@@ -73,8 +73,8 @@ module small_hb_int
      final_round (.clk(clk),.in(accum),.out(accum_rnd));
 
    wire [WIDTH-1:0] 	 clipped;
-   clip_reg #(.bits_in(WIDTH+3),.bits_out(WIDTH))
-     final_clip (.clk(clk),.in(accum_rnd),.out(clipped));
+   clip_reg #(.bits_in(WIDTH+3),.bits_out(WIDTH)) final_clip
+     (.clk(clk),.in(accum_rnd),.strobe_in(1'b1), .out(clipped));
 
    reg [WIDTH-1:0] 	 saved, saved_d3;
    always @(posedge clk)