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/*

 Asynchronous SDM NoC

 (C)2011 Wei Song

 Advanced Processor Technologies Group

 Computer Science, the Univ. of Manchester, UK

 Authors:

 Wei Song     wsong83@gmail.com

 License: LGPL 3.0 or later

 Input buffer for Wormhole/SDM routers.

 *** SystemVerilog is used ***

 References

 * Lookahead pipelines

     Montek Singh and Steven M. Nowick, The design of high-performance dynamic asynchronous pipelines: lookahead style, IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 2007(15), 1256-1269. doi:10.1109/TVLSI.2007.902205

 * Channel slicing

     Wei Song and Doug Edwards, A low latency wormhole router for asynchronous on-chip networks, Asia and South Pacific Design Automation Conference, 2010, 437-443.

 * SDM

     Wei Song and Doug Edwards, Asynchronous spatial division multiplexing router, Microprocessors and Microsystems, 2011(35), 85-97.

 History:

 05/05/2009  Initial version. <wsong83@gmail.com>

 20/09/2010  Supporting channel slicing and SDM using macro difinitions. <wsong83@gmail.com>

 24/05/2011  Clean up for opensource. <wsong83@gmail.com>

*/

// the router structure definitions

`include "define.v"

module inp_buf (/*AUTOARG*/

   // Outputs

   o0, o1, o2, o3, o4, ia, arb_r,

   // Inputs

   rst_n, i0, i1, i2, i3, i4, oa, addrx, addry, arb_ra

   );

   //-------------------------- parameters ---------------------------------------//

   parameter DIR = 0;              // the port direction: south, west, north, east, and local

   parameter RN = 4;               // the number of request outputs, must match the direction

   parameter DW = 16;              // the data-width of the data-path

   parameter PD = 2;               // the depth of the input buffer

   parameter SCN = DW/2;

   //-------------------------- I/O ports ---------------------------------------//

   input                  rst_n;          // global reset, active low

   input [SCN-1:0]         i0, i1, i2, i3; // data input

   output [SCN-1:0]        o0, o1, o2, o3; // data output

`ifdef ENABLE_CHANNEL_SLICING

   input [SCN-1:0]         i4, oa;

   output [SCN-1:0]        o4, ia;

`else

   input                  i4, oa;

   output                 o4, ia;

`endif

   input [7:0]             addrx, addry;

   output [RN-1:0]         arb_r;

   input                  arb_ra;

   //-------------------------- control signals ---------------------------------------//

   wire                   rten;                // routing enable

   wire                   frame_end;           // identify the end of a frame

   wire [7:0]              pipe_xd, pipe_yd;    // the target address from the incoming frame

   wire [PD:0][SCN-1:0]   pd0, pd1, pd2, pd3;  // data wires for the internal pipeline satges

   wire [5:0]              raw_dec;             // the routing decision from the comparator

   wire [4:0]              dec_reg;             // the routing decision kept by C-gates

   wire                   x_equal;             // addr x = target x

   wire                   rt_err;              // route decoder error

   wire                   rt_ack;              // route build ack

`ifdef ENABLE_CHANNEL_SLICING

   wire [SCN-1:0]          rtrst;               // rt decoder reset for each sub-channel

   wire [PD:0][SCN-1:0]   pd4, pda, pdan;      // data wires for the internal pipeline stages

`else

   wire                   rtrst;               // rt decode reset

   wire [PD:0]             pd4, pda, pdan;      // data wires for the internal pipeline satges

`endif // !`ifdef ENABLE_CHANNEL_SLICING

   genvar                 i, j;

   //------------------------- pipelines ------------------------------------- //

   generate for(i=0; i<PD; i++) begin: DP

`ifdef ENABLE_CHANNEL_SLICING

      for(j=0; j<SCN; j++) begin: SC

         pipe4 #(.DW(2))

         P (

            .o0  ( pd0[i][j]   ),

            .o1  ( pd1[i][j]   ),

            .o2  ( pd2[i][j]   ),

            .o3  ( pd3[i][j]   ),

            .o4  ( pd4[i][j]   ),

            .ia  ( pda[i+1][j] ),

            .i0  ( pd0[i+1][j] ),

            .i1  ( pd1[i+1][j] ),

            .i2  ( pd2[i+1][j] ),

            .i3  ( pd3[i+1][j] ),

            .i4  ( pd4[i+1][j] ),

            .oa  ( pdan[i][j]  )

            );

      end // block: SC

`else // !`ifdef ENABLE_CHANNEL_SLICING

      pipe4 #(.DW(DW))

      P (

         .o0  ( pd0[i]   ),

         .o1  ( pd1[i]   ),

         .o2  ( pd2[i]   ),

         .o3  ( pd3[i]   ),

         .o4  ( pd4[i]   ),

         .ia  ( pda[i+1] ),

         .i0  ( pd0[i+1] ),

         .i1  ( pd1[i+1] ),

         .i2  ( pd2[i+1] ),

         .i3  ( pd3[i+1] ),

         .i4  ( pd4[i+1] ),

         .oa  ( pdan[i]  )

         );

`endif // !`ifdef ENABLE_CHANNEL_SLICING

   end // block: DP

   endgenerate

   generate for(i=1; i<PD; i++) begin: DPA

      assign pdan[i] = rst_n ? ~(pda[i]|pd4[i-1]) : 0;

   end

   endgenerate

   assign ia = pda[PD]|pd4[PD-1];

   assign pd0[PD] = i0;

   assign pd1[PD] = i1;

   assign pd2[PD] = i2;

   assign pd3[PD] = i3;

   assign pd4[PD] = i4;

   assign o0 = pd0[0];

   assign o1 = pd1[0];

   assign o2 = pd2[0];

   assign o3 = pd3[0];

   assign o4 = pd4[0];

   //---------------------------- route decoder related -------------------------- //

   // fetch the x and y target

   and Px_0 (pipe_xd[0], rten, pd0[1][0]);

   and Px_1 (pipe_xd[1], rten, pd1[1][0]);

   and Px_2 (pipe_xd[2], rten, pd2[1][0]);

   and Px_3 (pipe_xd[3], rten, pd3[1][0]);

   and Px_4 (pipe_xd[4], rten, pd0[1][1]);

   and Px_5 (pipe_xd[5], rten, pd1[1][1]);

   and Px_6 (pipe_xd[6], rten, pd2[1][1]);

   and Px_7 (pipe_xd[7], rten, pd3[1][1]);

   and Py_0 (pipe_yd[0], rten, pd0[1][2]);

   and Py_1 (pipe_yd[1], rten, pd1[1][2]);

   and Py_2 (pipe_yd[2], rten, pd2[1][2]);

   and Py_3 (pipe_yd[3], rten, pd3[1][2]);

   and Py_4 (pipe_yd[4], rten, pd0[1][3]);

   and Py_5 (pipe_yd[5], rten, pd1[1][3]);

   and Py_6 (pipe_yd[6], rten, pd2[1][3]);

   and Py_7 (pipe_yd[7], rten, pd3[1][3]);

   routing_decision      // the comparator

   RTD(

       .addrx      ( addrx   )

       ,.addry     ( addry   )

       ,.pipe_xd   ( pipe_xd )

       ,.pipe_yd   ( pipe_yd )

       ,.decision  ( raw_dec )

       );

   // keep the routing decision until the tail flit is received by all sub-channels

   c2p C_RTD0  ( .b(raw_dec[0]),      .a((~frame_end)&rst_n),    .q(dec_reg[0]));

   c2p C_RTD1  ( .b(raw_dec[1]),      .a((~frame_end)&rst_n),    .q(dec_reg[1]));

   c2p C_RT_XEQ (.b(raw_dec[2]),      .a((~frame_end)&rst_n),    .q(x_equal) );

   c2p C_RTD2  ( .b(raw_dec[3]),      .a(x_equal),               .q(dec_reg[2]));

   c2p C_RTD3  ( .b(raw_dec[4]),      .a(x_equal),               .q(dec_reg[3]));

   c2p C_RTD4  ( .b(raw_dec[5]),      .a(x_equal),               .q(dec_reg[4]));

   // generate the arbiter request signals

   assign arb_r =

                  DIR == 0 ? {dec_reg[4],dec_reg[2],dec_reg[1],dec_reg[3]} :   // south port

                  DIR == 1 ? {dec_reg[4],dec_reg[2]}                       :   // west port

                  DIR == 2 ? {dec_reg[4],dec_reg[2],dec_reg[3],dec_reg[0]} :   // north port

                  DIR == 3 ? {dec_reg[4],dec_reg[3]}                       :   // east port

                             {dec_reg[2],dec_reg[1],dec_reg[3],dec_reg[0]} ;   // local port

   assign rt_err =

                  DIR == 0 ? |{dec_reg[0]}                        :   // south port

                  DIR == 1 ? |{dec_reg[0],dec_reg[1],dec_reg[3]}  :   // west port

                  DIR == 2 ? |{dec_reg[1]}                        :   // north port

                  DIR == 3 ? |{dec_reg[0],dec_reg[1],dec_reg[2]}  :   // east port

                             |{dec_reg[4]}                        ;   // local port

   or IP_RTACK (rt_ack, rt_err, arb_ra);

   // ------------------------ pipeline control ------------------------------ //

`ifdef ENABLE_CHANNEL_SLICING

   for(j=0; j<SCN; j++) begin: SC

      // the sub-channel controller

      subc_ctl SCH_C (

                      .nack     ( pdan[0][j]  ),

                      .rt_rst   ( rtrst[j]    ),

                      .ai2cb    ( oa[j]       ),

                      .ack      ( pda[1][j]   ),

                      .eof      ( pd4[0][j]   ),

                      .rt_ra    ( rt_ack      ),

                      .rt_err   ( rt_err      ),

                      .rst_n    ( rst_n       )

                      );

   end // block: SC

`else // !`ifdef ENABLE_CHANNEL_SLICING

   subc_ctl SCH_C (

                   .nack     ( pdan[0]  ),

                   .rt_rst   ( rtrst    ),

                   .ai2cb    ( oa       ),

                   .ack      ( pda[1]   ),

                   .eof      ( pd4[0]   ),

                   .rt_ra    ( rt_ack   ),

                   .rt_err   ( rt_err   ),

                   .rst_n    ( rst_n    )

                   );

`endif // !`ifdef ENABLE_CHANNEL_SLICING

   // the router controller part

   assign rten = ~rt_ack;

   assign frame_end = &rtrst;

endmodule // inp_buf

// the routing decision making procedure, comparitors

module routing_decision (

                         addrx

                         ,addry

                         ,pipe_xd

                         ,pipe_yd

                         ,decision

                         );

   // compare with (2,3)

   input [7:0] addrx;

   input [7:0] addry;

   input   [7:0]   pipe_xd;

   input [7:0]      pipe_yd;

   output [5:0]    decision;

   wire [2:0]       x_cmp [1:0];

   wire [2:0]       y_cmp [1:0];

   chain_comparator X0 ( .a(pipe_xd[3:0]), .b(addrx[3:0]), .q(x_cmp[0]));

   chain_comparator X1 ( .a(pipe_xd[7:4]), .b(addrx[7:4]), .q(x_cmp[1]));

   chain_comparator Y0 ( .a(pipe_yd[3:0]), .b(addry[3:0]), .q(y_cmp[0]));

   chain_comparator Y1 ( .a(pipe_yd[7:4]), .b(addry[7:4]), .q(y_cmp[1]));

   assign decision[0] = x_cmp[1][0] | (x_cmp[1][2]&x_cmp[0][0]);       // frame x > addr x

   assign decision[1] = x_cmp[1][1] | (x_cmp[1][2]&x_cmp[0][1]);       // frame x < addr x

   assign decision[2] = x_cmp[1][2] & x_cmp[0][2];                     // frame x = addr x

   assign decision[3] = y_cmp[1][0] | (y_cmp[1][2]&y_cmp[0][0]);       // frame y > addr y

   assign decision[4] = y_cmp[1][1] | (y_cmp[1][2]&y_cmp[0][1]);       // frame y < addr y

   assign decision[5] = y_cmp[1][2] & y_cmp[0][2];                     // frame y = addr y

endmodule // routing_decision

// the 1-of-4 comparator

module chain_comparator (

     a

    ,b

    ,q

    );

   input   [3:0]   a;

   input [3:0]      b;

   output [2:0]    q;

   // a > b

   assign q[0] = (a[3]&(|b[2:0])) | (a[2]&(|b[1:0])) | (a[1]&(|b[0:0]));

   // a < b

   assign q[1] = (a[2]&(|b[3:3])) | (a[1]&(|b[3:2])) | (a[0]&(|b[3:1]));

   // a = b

   assign q[2] = (a[3]&b[3]) | (a[2]&b[2]) | (a[1]&b[1]) | (a[0]&b[0]);

endmodule // chain_comparator