Subversion Repositories openrisc_2011-10-31

module ram_wb ( dat_i, dat_o, adr_i, we_i, sel_i, cyc_i, stb_i, ack_o, cti_i, clk_i, rst_i);

   parameter dat_width = 32;

   parameter adr_width = 12;

   parameter mem_size  = 262144; // Default is 1MB (262144 32-bit words)

   // wishbone signals

   input [31:0]          dat_i;

   output [31:0]         dat_o;

   input [adr_width-1:2] adr_i;

   input                 we_i;

   input [3:0]            sel_i;

   input                 cyc_i;

   input                 stb_i;

   output reg            ack_o;

   input [2:0]            cti_i;

   // clock

   input                 clk_i;

   // async reset

   input                 rst_i;

   wire [31:0]            wr_data;

   // mux for data to ram

   assign wr_data[31:24] = sel_i[3] ? dat_i[31:24] : dat_o[31:24];

   assign wr_data[23:16] = sel_i[2] ? dat_i[23:16] : dat_o[23:16];

   assign wr_data[15: 8] = sel_i[1] ? dat_i[15: 8] : dat_o[15: 8];

   assign wr_data[ 7: 0] = sel_i[0] ? dat_i[ 7: 0] : dat_o[ 7: 0];

   ram_wb_sc_sw

     #

     (

      .dat_width(dat_width),

      .adr_width(adr_width),

      .mem_size(mem_size)

      )

     ram0

     (

      .dat_i(wr_data),

      .dat_o(dat_o),

      .adr_i({2'b00, adr_i}),

      .we_i(we_i & ack_o),

      .clk(clk_i)

      );

   // ack_o

   always @ (posedge clk_i or posedge rst_i)

     if (rst_i)

       ack_o <= 1'b0;

     else

       if (!ack_o)

         begin

            if (cyc_i & stb_i)

              ack_o <= 1'b1;

         end

       else

         ack_o <= 1'b0;

   // We did have acking logic which was sensitive to the

   // burst signals, cti_i, but this proved to cause problems

   // and we were never receiving back-to-back reads or writes

   // anyway. This logic which only acks one transaction at a

   // time appears to work well, despite not supporting burst

   // transactions.

endmodule