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///////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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// Filename: wbarbiter.v
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// Filename: wbarbiter.v
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//
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//
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// Project: Zip CPU -- a small, lightweight, RISC CPU soft core
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// Project: Zip CPU -- a small, lightweight, RISC CPU soft core
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//
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//
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//
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//
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//
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//
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// Creator: Dan Gisselquist, Ph.D.
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// Creator: Dan Gisselquist, Ph.D.
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// Gisselquist Technology, LLC
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// Gisselquist Technology, LLC
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//
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//
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///////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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// Copyright (C) 2015, Gisselquist Technology, LLC
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// Copyright (C) 2015,2017, Gisselquist Technology, LLC
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//
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//
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// This program is free software (firmware): you can redistribute it and/or
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// This program is free software (firmware): you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as published
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// modify it under the terms of the GNU General Public License as published
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// by the Free Software Foundation, either version 3 of the License, or (at
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// by the Free Software Foundation, either version 3 of the License, or (at
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// your option) any later version.
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// your option) any later version.
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// This program is distributed in the hope that it will be useful, but WITHOUT
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// This program is distributed in the hope that it will be useful, but WITHOUT
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// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
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// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// for more details.
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//
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//
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// You should have received a copy of the GNU General Public License along
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// with this program. (It's in the $(ROOT)/doc directory, run make with no
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// target there if the PDF file isn't present.) If not, see
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// <http://www.gnu.org/licenses/> for a copy.
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//
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// License: GPL, v3, as defined and found on www.gnu.org,
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// License: GPL, v3, as defined and found on www.gnu.org,
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// http://www.gnu.org/licenses/gpl.html
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// http://www.gnu.org/licenses/gpl.html
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//
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//
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//
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//
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///////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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//
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// `define WBA_ALTERNATING
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`define WBA_ALTERNATING
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module wbarbiter(i_clk, i_rst,
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module wbarbiter(i_clk, i_rst,
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// Bus A -- gets priority when not alternating
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// Bus A
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i_a_adr, i_a_dat, i_a_we, i_a_stb, i_a_cyc, o_a_ack, o_a_stall, o_a_err,
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i_a_cyc, i_a_stb, i_a_we, i_a_adr, i_a_dat, i_a_sel, o_a_ack, o_a_stall, o_a_err,
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// Bus B
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// Bus B
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i_b_adr, i_b_dat, i_b_we, i_b_stb, i_b_cyc, o_b_ack, o_b_stall, o_b_err,
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i_b_cyc, i_b_stb, i_b_we, i_b_adr, i_b_dat, i_b_sel, o_b_ack, o_b_stall, o_b_err,
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// Both buses
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// Both buses
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o_adr, o_dat, o_we, o_stb, o_cyc, i_ack, i_stall, i_err);
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o_cyc, o_stb, o_we, o_adr, o_dat, o_sel, i_ack, i_stall, i_err);
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// 18 bits will address one GB, 4 bytes at a time.
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// 18 bits will address one GB, 4 bytes at a time.
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// 19 bits will allow the ability to address things other than just
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// 19 bits will allow the ability to address things other than just
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// the 1GB of memory we are expecting.
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// the 1GB of memory we are expecting.
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parameter DW=32, AW=19;
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parameter DW=32, AW=19;
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// Wishbone doesn't use an i_ce signal. While it could, they dislike
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// Wishbone doesn't use an i_ce signal. While it could, they dislike
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// what it would (might) do to the synchronous reset signal, i_rst.
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// what it would (might) do to the synchronous reset signal, i_rst.
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input i_clk, i_rst;
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input i_clk, i_rst;
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input [(AW-1):0] i_a_adr, i_b_adr;
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input [(AW-1):0] i_a_adr, i_b_adr;
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input [(DW-1):0] i_a_dat, i_b_dat;
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input [(DW-1):0] i_a_dat, i_b_dat;
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input [(DW/8-1):0] i_a_sel, i_b_sel;
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input i_a_we, i_a_stb, i_a_cyc;
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input i_a_we, i_a_stb, i_a_cyc;
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input i_b_we, i_b_stb, i_b_cyc;
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input i_b_we, i_b_stb, i_b_cyc;
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output wire o_a_ack, o_b_ack, o_a_stall, o_b_stall,
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output wire o_a_ack, o_b_ack, o_a_stall, o_b_stall,
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o_a_err, o_b_err;
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o_a_err, o_b_err;
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output wire [(AW-1):0] o_adr;
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output wire [(AW-1):0] o_adr;
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output wire [(DW-1):0] o_dat;
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output wire [(DW-1):0] o_dat;
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output wire [(DW/8-1):0] o_sel;
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output wire o_we, o_stb, o_cyc;
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output wire o_we, o_stb, o_cyc;
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input i_ack, i_stall, i_err;
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input i_ack, i_stall, i_err;
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// All the fancy stuff here is done with the three primary signals:
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// All the fancy stuff here is done with the three primary signals:
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// o_cyc
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// o_cyc
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// Realistically, if neither master owns the bus, the output is a
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// Realistically, if neither master owns the bus, the output is a
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// don't care. Thus we trigger off whether or not 'A' owns the bus.
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// don't care. Thus we trigger off whether or not 'A' owns the bus.
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// If 'B' owns it all we care is that 'A' does not. Likewise, if
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// If 'B' owns it all we care is that 'A' does not. Likewise, if
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// neither owns the bus than the values on the various lines are
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// neither owns the bus than the values on the various lines are
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// irrelevant.
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// irrelevant. (This allows us to get two outputs per Xilinx 6-LUT)
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assign o_stb = (o_cyc) && ((w_a_owner) ? i_a_stb : i_b_stb);
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assign o_we = (w_a_owner) ? i_a_we : i_b_we;
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assign o_adr = (w_a_owner) ? i_a_adr : i_b_adr;
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assign o_adr = (w_a_owner) ? i_a_adr : i_b_adr;
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assign o_dat = (w_a_owner) ? i_a_dat : i_b_dat;
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assign o_dat = (w_a_owner) ? i_a_dat : i_b_dat;
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assign o_we = (w_a_owner) ? i_a_we : i_b_we;
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assign o_sel = (w_a_owner) ? i_a_sel : i_b_sel;
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assign o_stb = (o_cyc) && ((w_a_owner) ? i_a_stb : i_b_stb);
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// We cannot allow the return acknowledgement to ever go high if
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// We cannot allow the return acknowledgement to ever go high if
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// the master in question does not own the bus. Hence we force it
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// the master in question does not own the bus. Hence we force it
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// low if the particular master doesn't own the bus.
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// low if the particular master doesn't own the bus.
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assign o_a_ack = (w_a_owner) ? i_ack : 1'b0;
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assign o_a_ack = (w_a_owner) ? i_ack : 1'b0;
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