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[/] [zipcpu/] [trunk/] [rtl/] [aux/] [busdelay.v] - Rev 195
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//////////////////////////////////////////////////////////////////////////////// // // Filename: busdelay.v // // Project: Zip CPU -- a small, lightweight, RISC CPU soft core // // Purpose: Delay any access to the wishbone bus by a single clock. // // When the first Zip System would not meet the timing requirements of // the board it was placed upon, this bus delay was added to help out. // It may no longer be necessary, having cleaned some other problems up // first, but it will remain here as a means of alleviating timing // problems. // // The specific problem takes place on the stall line: a wishbone master // *must* know on the first clock whether or not the bus will stall. // // // After a period of time, I started a new design where the timing // associated with this original bus clock just wasn't ... fast enough. // I needed to delay the stall line as well. A new busdelay was then // written and debugged whcih delays the stall line. (I know, you aren't // supposed to delay the stall line--but what if you *have* to in order // to meet timing?) This new logic has been merged in with the old, // and the DELAY_STALL line can be set to non-zero to use it instead // of the original logic. Don't use it if you don't need it: it will // consume resources and slow your bus down more, but if you do need // it--don't be afraid to use it. // // Both versions of the bus delay will maintain a single access per // clock when pipelined, they only delay the time between the strobe // going high and the actual command being accomplished. // // // Creator: Dan Gisselquist, Ph.D. // Gisselquist Technology, LLC // //////////////////////////////////////////////////////////////////////////////// // // Copyright (C) 2015-2016, Gisselquist Technology, LLC // // This program is free software (firmware): you can redistribute it and/or // modify it under the terms of the GNU General Public License as published // by the Free Software Foundation, either version 3 of the License, or (at // your option) any later version. // // This program is distributed in the hope that it will be useful, but WITHOUT // ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License // for more details. // // License: GPL, v3, as defined and found on www.gnu.org, // http://www.gnu.org/licenses/gpl.html // // //////////////////////////////////////////////////////////////////////////////// // module busdelay(i_clk, // The input bus i_wb_cyc, i_wb_stb, i_wb_we, i_wb_addr, i_wb_data, o_wb_ack, o_wb_stall, o_wb_data, o_wb_err, // The delayed bus o_dly_cyc, o_dly_stb, o_dly_we, o_dly_addr, o_dly_data, i_dly_ack, i_dly_stall, i_dly_data, i_dly_err); parameter AW=32, DW=32, DELAY_STALL = 0; input i_clk; // Input/master bus input i_wb_cyc, i_wb_stb, i_wb_we; input [(AW-1):0] i_wb_addr; input [(DW-1):0] i_wb_data; output reg o_wb_ack; output wire o_wb_stall; output reg [(DW-1):0] o_wb_data; output wire o_wb_err; // Delayed bus output reg o_dly_cyc, o_dly_stb, o_dly_we; output reg [(AW-1):0] o_dly_addr; output reg [(DW-1):0] o_dly_data; input i_dly_ack; input i_dly_stall; input [(DW-1):0] i_dly_data; input i_dly_err; generate if (DELAY_STALL != 0) begin reg r_stb, r_we, r_rtn_stall, r_rtn_err; reg [(DW-1):0] r_data; reg [(AW-1):0] r_addr; initial o_dly_cyc = 1'b0; initial r_rtn_stall= 1'b0; initial r_stb = 1'b0; always @(posedge i_clk) begin o_dly_cyc <= (i_wb_cyc); if (!i_dly_stall) begin r_we <= i_wb_we; r_addr <= i_wb_addr; r_data <= i_wb_data; if (r_stb) begin o_dly_we <= r_we; o_dly_addr <= r_addr; o_dly_data <= r_data; o_dly_stb <= 1'b1; r_rtn_stall <= 1'b0; r_stb <= 1'b0; end else begin o_dly_we <= i_wb_we; o_dly_addr <= i_wb_addr; o_dly_data <= i_wb_data; o_dly_stb <= i_wb_stb; r_stb <= 1'b0; r_rtn_stall <= 1'b0; end end else if ((!r_stb)&&(!o_wb_stall)) begin r_we <= i_wb_we; r_addr <= i_wb_addr; r_data <= i_wb_data; r_stb <= i_wb_stb; r_rtn_stall <= i_wb_stb; end if (!i_wb_cyc) begin o_dly_stb <= 1'b0; r_stb <= 1'b0; r_rtn_stall <= 1'b0; end o_wb_ack <= (i_dly_ack)&&(i_wb_cyc)&&(o_dly_cyc); o_wb_data <= i_dly_data; r_rtn_err <= (i_dly_err)&&(i_wb_cyc)&&(o_dly_cyc); end assign o_wb_stall = r_rtn_stall; assign o_wb_err = r_rtn_err; end else begin initial o_dly_cyc = 1'b0; initial o_dly_stb = 1'b0; always @(posedge i_clk) o_dly_cyc <= i_wb_cyc; // Add the i_wb_cyc criteria here, so we can simplify the // o_wb_stall criteria below, which would otherwise *and* // these two. always @(posedge i_clk) if (~o_wb_stall) o_dly_stb <= ((i_wb_cyc)&&(i_wb_stb)); always @(posedge i_clk) if (~o_wb_stall) o_dly_we <= i_wb_we; always @(posedge i_clk) if (~o_wb_stall) o_dly_addr<= i_wb_addr; always @(posedge i_clk) if (~o_wb_stall) o_dly_data <= i_wb_data; always @(posedge i_clk) o_wb_ack <= (i_dly_ack)&&(o_dly_cyc)&&(i_wb_cyc); always @(posedge i_clk) o_wb_data <= i_dly_data; // Our only non-delayed line, yet still really delayed. Perhaps // there's a way to register this? // o_wb_stall <= (i_wb_cyc)&&(i_wb_stb) ... or some such? // assign o_wb_stall=((i_wb_cyc)&&(i_dly_stall)&&(o_dly_stb));//&&o_cyc assign o_wb_stall = ((i_dly_stall)&&(o_dly_stb));//&&o_cyc assign o_wb_err = i_dly_err; end endgenerate endmodule
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