source: XOpenSparcT1/trunk/T1-CPU/tlu/tlu_rrobin_picker.v @ 6

// ========== Copyright Header Begin ==========================================
// 
// OpenSPARC T1 Processor File: tlu_rrobin_picker.v
// Copyright (c) 2006 Sun Microsystems, Inc.  All Rights Reserved.
// DO NOT ALTER OR REMOVE COPYRIGHT NOTICES.
// 
// The above named program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public
// License version 2 as published by the Free Software Foundation.
// 
// The above named 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 work; if not, write to the Free Software
// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
// 
// ========== Copyright Header End ============================================
////////////////////////////////////////////////////////////////////////
/*
//      Description:    Round-Robin Picker for 4 eventss.
//                      Differs from lsu'v rrobin picker by the
//                      fact that there is no default 1-hot event.
*/
////////////////////////////////////////////////////////////////////////
// Global header file includes
////////////////////////////////////////////////////////////////////////
`include        "sys.h" // system level definition file which contains the
                                        // time scale definition

module tlu_rrobin_picker (/*AUTOARG*/
   // Outputs
   pick_one_hot, 
   // Inputs
   events, tlu_rst_l, clk
   );

input   [3:0]   events ;                // multi-hot; events that could be chosen
// this siganl was modified to abide to the Niagara reset methodology
input           tlu_rst_l ;                     // reset - active low
input           clk ;

output  [3:0]   pick_one_hot ;  // one-hot; events that must be chosen
//
// this signal was added to abide to the Niagara reset methodology
wire    tlu_rst ;       

// This section was modified to abide to the Niagara synthesis methodology
//
// reg  [3:0]   pick_status ;   
wire    pick_status_reset ;     
wire    [3:0]   pick_status_in ;        
wire    [3:0]   pick_status ;   

wire    events_unpicked ;
wire    [3:0]   pe_mask ;

//
// this signal was added to abide to the Niagara reset methodology
assign tlu_rst = ~tlu_rst_l;

assign  events_unpicked = |(events[3:0] & ~pick_status[3:0]) ;
                        // term replicated.

// priority encode mask
assign  pe_mask[3:0] =
                events_unpicked ? 
                (events[3:0] & ~pick_status[3:0]) :     // choose from eventss that have not picked.
                events[3:0] ;                           // else all eventss on equal terms

assign  pick_one_hot[0] = 
                pe_mask[0] ;
                //pe_mask[0] | ~(|pe_mask[3:0]);                // none requesting then 0 is forced hot
assign  pick_one_hot[1] = 
                pe_mask[1] & ~pe_mask[0] ;
assign  pick_one_hot[2] = 
                pe_mask[2] & ~(|pe_mask[1:0]) ;
assign  pick_one_hot[3] = 
                pe_mask[3] & ~(|pe_mask[2:0]) ;

// This section was modified to abide to the Niagara synthesis methodology
//
// Define Pick Status
//always        @ (posedge clk)
//      begin
//              if ((&(pick_status[3:0] | pick_one_hot[3:0])) | tlu_rst) 
//                      pick_status[3:0] <= 4'b0000 ;   // clear pick_status
//              else
//                      pick_status[3:0] <= pick_status[3:0] | pick_one_hot[3:0] ;
//                                      // term replicated
//      end

assign pick_status_reset = (&(pick_status[3:0] | pick_one_hot[3:0])) | tlu_rst;
assign pick_status_in    = pick_status[3:0] | pick_one_hot[3:0]; 

dffr_s #(4)  dffre_pick_status  (
        .din (pick_status_in[3:0]), .q (pick_status[3:0]),
        .rst (pick_status_reset), .clk (clk),
        .se  (1'b0),  .si  (),       .so ()
        );

endmodule