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dgisselq |
////////////////////////////////////////////////////////////////////////////////
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//
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// Filename: wbuidleint.v
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//
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// Project: XuLA2 board
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//
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// Purpose: Creates an output for the interface, inserting idle words and
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// words indicating an interrupt has taken place into the output
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// stream. Henceforth, the output means more than just bus transaction
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// results. It may mean there is no bus transaction result to report,
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// or that an interrupt has taken place.
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//
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//
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// Creator: Dan Gisselquist, Ph.D.
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// Gisselquist Technology, LLC
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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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//
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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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// 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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//
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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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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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//
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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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//
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//
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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module wbuidleint(i_clk, i_stb, i_codword, i_cyc, i_busy, i_int,
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o_stb, o_codword, o_busy,
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i_tx_busy);
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input i_clk;
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// From the FIFO following the bus executor
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input i_stb;
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input [35:0] i_codword;
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// From the rest of the board
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input i_cyc, i_busy, i_int;
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// To the next stage
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output reg o_stb;
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output reg [35:0] o_codword;
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output reg o_busy;
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// Is the next stage busy?
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input i_tx_busy;
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reg int_request, int_sent;
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initial int_request = 1'b0;
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always @(posedge i_clk)
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if((o_stb)&&(~i_tx_busy)&&(o_codword[35:30]==6'h4))
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int_request <= i_int;
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else
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int_request <= (int_request)||(i_int);
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// Now, for the idle counter
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wire idle_expired;
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reg idle_state;
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reg [35:0] idle_counter;
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initial idle_counter = 36'h0000;
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always @(posedge i_clk)
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if ((i_stb)||(o_stb))
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idle_counter <= 36'h000;
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else if (~idle_counter[35])
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idle_counter <= idle_counter + 36'd43;
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initial idle_state = 1'b0;
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always @(posedge i_clk)
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if ((o_stb)&&(~i_tx_busy)&&(o_codword[35:31]==5'h0))
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idle_state <= 1'b1;
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else if (~idle_counter[35])
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idle_state <= 1'b0;
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assign idle_expired = (~idle_state)&&(idle_counter[35]);
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initial o_stb = 1'b0;
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initial o_busy = 1'b0;
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always @(posedge i_clk)
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if ((o_stb)&&(i_tx_busy))
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begin
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o_busy <= 1'b1;
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end else if (o_stb) // and not i_tx_busy
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begin
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// Idle one clock before becoming not busy
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o_stb <= 1'b0;
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o_busy <= 1'b1;
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end else if (o_busy)
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o_busy <= 1'b0;
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else if (i_stb) // and (~o_busy)&&(~o_stb)
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begin // On a valid output, just send it out
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// We'll open this strobe, even if the transmitter
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// is busy, just 'cause we might otherwise lose it
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o_codword <= i_codword;
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o_stb <= 1'b1;
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o_busy <= 1'b1;
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end else if ((int_request)&&(~int_sent))
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begin
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o_stb <= 1'b1;
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o_codword <= { 6'h4, 30'h0000 }; // interrupt codeword
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o_busy <= 1'b1;
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end else if (idle_expired)
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begin // Strobe, if we're not writing or our
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// last command wasn't an idle
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o_stb <= 1'b1;
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o_busy <= 1'b1;
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if (i_cyc)
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o_codword <= { 6'h1, 30'h0000 }; // idle codeword, bus busy
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else
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o_codword <= { 6'h0, 30'h0000 };
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end
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initial int_sent = 1'b0;
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always @(posedge i_clk)
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if ((int_request)&&((~o_stb)&&(~o_busy)&&(~i_stb)))
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int_sent <= 1'b1;
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else if (~i_int)
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int_sent <= 1'b0;
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endmodule
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