dsp: new rounding. more complex, but better properties

1 files changed, 19 insertions, 3 deletions

diff --git a/usrp2/sdr_lib/round.v b/usrp2/sdr_lib/round.v
index 7a137d702..5b83981c6 100644
--- a/usrp2/sdr_lib/round.v
+++ b/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 +24,28 @@
 
 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;
+   wire 			 round_corr_trunc = 0;
+   wire 			 round_corr_rtz = (in[bits_in-1] & |in[bits_in-bits_out-1:0]);
+   wire 			 round_corr_nearest = in[bits_in-bits_out-1];
+   wire 			 round_corr_nearest_safe = (~in[bits_in-1] & (&in[bits_in-2:bits_out])) ? 0 :
+				 round_corr_nearest;
+      
+   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