sound.v: Change the one-shot generator to handle short inhibit pulses

The BASIC interpreter sends 0x00 (clear) and 0x83 (beep) in very short
order.  We have to clear the oneshot immediately, not on the next
strobe.

1 files changed, 20 insertions, 10 deletions

diff --git a/sound.v b/sound.v
index ad3a0a7..5e8fa46 100644
--- a/sound.v
+++ b/sound.v
@@ -1,4 +1,15 @@
-// $Id$
+// -----------------------------------------------------------------------
+//
+//   Copyright 2003-2015 H. Peter Anvin - All Rights Reserved
+//
+//   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, Inc., 53 Temple Place Ste 330,
+//   Bostom MA 02111-1307, USA; either version 2 of the License, or
+//   (at your option) any later version; incorporated herein by reference.
+//
+// -----------------------------------------------------------------------
+
 //
 // Sound controller for ABC80
 //
@@ -152,16 +163,15 @@ module oneshot(
    wire 	      ctr_or = |ctr;
       
    always @(posedge clk)
-     if ( clk_en )
-       begin
-	  inhibit1 <= inhibit;
-	  oneshot  <= ctr_or;
+     begin
+	inhibit1 <= inhibit;
+	oneshot  <= ctr_or;
 	  
-	  if ( ~inhibit & inhibit1 )
-	    ctr <= 11'd1624;	// ~26 ms
-	  else if ( ctr_or )
-	    ctr <= ctr - 1;
-       end
+	if ( ~inhibit & inhibit1 )
+	  ctr <= 11'd1624;	// ~26 ms
+	else if ( ctr_or & clk_en )
+	  ctr <= ctr - 1;
+     end
 endmodule // oneshot
 
 module envelope_select(