design/sys/iop/niu/rtl/niu_pio_ucb_in32.v

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// OpenSPARC T2 Processor File: niu_pio_ucb_in32.v
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////////////////////////////////////////////////////////////////////////////////
//
//
//  Copyright (C) 2003 by Sun Microsystems, Inc.
//
//  All rights reserved. No part of this design may be reproduced,
//  stored in a retrieval system, or transmitted, in any form or by
//  any means, electronic, mechanical, photocopying, recording, or
//  otherwise, without prior written permission of Sun Microsystems,
//  Inc.
//
//  Sun Proprietary/Confidential
//
//
//  Primary Contact:    Jimmy.Lau@sun.com x48745
//  Description:        This interface is modified based on Niagra ucb_bus_in.
//                      Instaniated by UCB modules and NCU to receive
//                      packets on the UCB bus. This module supports 32 bit
//                      data bus in.
//
//  Revision: 1. March 08, 2004 - John Lo
//               Changed modules name from
//               ucb_bus_in32_niu.v  to niu_pio_ucb_in32
//
//               Changed enl2clk to clk.
//
//
////////////////////////////////////////////////////////////////////////////////


module niu_pio_ucb_in32 (
                     // Global //
                     reset,
                     clk,
                     // UCB bus //
                     vld,
                     data,
                     stall,
                     // local unit //
                     indata_buf_vld,
                     indata_buf,
                     stall_a1 );

// Global interface
input          reset;
input          clk;


// UCB bus interface
input          vld;
input  [31:0]  data;
output         stall;


// Local interface
output         indata_buf_vld;
output [127:0] indata_buf;
input          stall_a1;

// Internal signals
wire           vld_d1;
wire           stall_d1;
wire  [31:0]   data_d1;
wire           skid_buf0_en;
wire           vld_buf0;
wire  [31:0]   data_buf0;
wire           skid_buf1_en;
wire           vld_buf1;
wire  [31:0]   data_buf1;
wire           skid_buf0_sel;
wire           skid_buf1_sel;
wire           vld_mux;
wire  [31:0]   data_mux;
wire  [3:0]    indata_vec_next;
wire  [3:0]    indata_vec;
wire  [127:0]  indata_buf_next;
wire           indata_vec0_d1;
wire           stall_a1_inv;


////////////////////////////////////////////////////////////////////////
// Code starts here
////////////////////////////////////////////////////////////////////////
/************************************************************
 * UCB bus interface flops
 * This is to make signals going between NCU and UCB flop-to-flop
 * to improve timing.
 ************************************************************/
dffre #(1) vld_d1_ff (.d(vld),
                          .reset(reset),
                          .en(~stall_d1),
                          .clk(clk),
                          .q(vld_d1) );

dffe #(32) data_d1_ff (.d(data[31:0]),
                          .en(~stall_d1),
                          .clk(clk),
                          .q(data_d1[31:0]) );

dffr #(1) stall_ff   (.d(stall_a1),
                          .clk(clk),
                          .reset(reset),
                          .q(stall) );

dffr #(1) stall_d1_ff (.d(stall),
                           .clk(clk),
                           .reset(reset),
                           .q(stall_d1) );


/************************************************************
 * Skid buffer
 * We need a two deep skid buffer to handle stalling.
 ************************************************************/
// Assertion: stall has to be deasserted for more than 1 cycle
//            ie time between two separate stalls has to be
//            at least two cycles.  Otherwise, contents from
//            skid buffer will be lost.

// Buffer 0
assign         skid_buf0_en = stall_a1 & ~stall;

dffre #(1) vld_buf0_ff (.d(vld_d1),
                            .reset(reset),
                            .en(skid_buf0_en),
                            .clk(clk),
                            .q(vld_buf0) );

dffe #(32) data_buf0_ff (.d(data_d1[31:0]),
                            .en(skid_buf0_en),
                            .clk(clk),
                            .q(data_buf0[31:0]) );

// Buffer 1
dffr #(1) skid_buf1_en_ff (.d(skid_buf0_en),
                               .clk(clk),
                               .reset(reset),
                               .q(skid_buf1_en) );

dffre #(1) vld_buf1_ff (.d(vld_d1),
                            .reset(reset),
                            .en(skid_buf1_en),
                            .clk(clk),
                            .q(vld_buf1) );

dffe #(32) data_buf1_ff (.d(data_d1[31:0]),
                            .en(skid_buf1_en),
                            .clk(clk),
                            .q(data_buf1[31:0]) );

/************************************************************
 * Mux between skid buffer and interface flop
 ************************************************************/
// Assertion: stall has to be deasserted for more than 1 cycle
//            ie time between two separate stalls has to be
//            at least two cycles.  Otherwise, contents from
//            skid buffer will be lost.

assign        skid_buf0_sel = ~stall_a1 & stall;

dffr #(1) skid_buf1_sel_ff (.d(skid_buf0_sel),
                                .clk(clk),
                                .reset(reset),
                                .q(skid_buf1_sel) );

assign        vld_mux = skid_buf0_sel ? vld_buf0 :
                        skid_buf1_sel ? vld_buf1 : vld_d1;

assign        data_mux[31:0] = skid_buf0_sel ? data_buf0[31:0] :
                               skid_buf1_sel ? data_buf1[31:0] : data_d1[31:0];


/************************************************************
 * Assemble inbound data
 ************************************************************/
// valid vector
assign         indata_vec_next[3:0] = {vld_mux,indata_vec[3:1]};
assign         stall_a1_inv = ~stall_a1 ;
dffre #(4) indata_vec_ff (.d(indata_vec_next[3:0]),
                              .en(stall_a1_inv),
                              .reset(reset),
                              .clk(clk),
                              .q(indata_vec[3:0]) );

// data buffer
assign  indata_buf_next[127:0] = {data_mux[31:0],indata_buf[127:32]};
dffe #(128) indata_buf_ff (.d(indata_buf_next[127:0]),
                              .en(stall_a1_inv),
                              .clk(clk),
                              .q(indata_buf[127:0]) );

// detect a new packet
dffre #(1) indata_vec0_d1_ff (.d(indata_vec[0]),
                                  .reset(reset),
                                  .en(stall_a1_inv),
                                  .clk(clk),
                                  .q(indata_vec0_d1) );

assign        indata_buf_vld = indata_vec[0] & ~indata_vec0_d1;


endmodule // niu_pio_ucb_in32