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[/] [xulalx25soc/] [trunk/] [rtl/] [wbudecompress.v] - Rev 25
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//////////////////////////////////////////////////////////////////////////////// // // Filename: wbudecompress.v // // Project: XuLA2 board // // Purpose: Compression via this interface is simply a lookup table. // When writing, if requested, rather than writing a new 36-bit // word, we may be asked to repeat a word that's been written recently. // That's the goal of this routine: if given a word's (relative) address // in the write stream, we use that address, else we expect a full 32-bit // word to come in to be written. // // // Creator: Dan Gisselquist, Ph.D. // Gisselquist Technology, LLC // //////////////////////////////////////////////////////////////////////////////// // // Copyright (C) 2015, 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 wbudecompress(i_clk, i_stb, i_word, o_stb, o_word); input i_clk, i_stb; input [35:0] i_word; output reg o_stb; output reg [35:0] o_word; // Clock zero // { o_stb, r_stb } = 0 wire cmd_write_not_compressed = (i_word[35:33] == 3'h3); // Clock one: { o_stb, r_stb } = 4'h1 when done reg [7:0] wr_addr; initial wr_addr = 8'h0; always @(posedge i_clk) if ((i_stb)&&(cmd_write_not_compressed)) wr_addr <= wr_addr + 8'h1; reg [31:0] compression_tbl [0:255]; always @(posedge i_clk) if (i_stb) compression_tbl[wr_addr] <= { i_word[32:31], i_word[29:0] }; reg [35:0] r_word; always @(posedge i_clk) if (i_stb) r_word <= i_word; // Clock two, calculate the table address ... 1 is the smallest address // { o_stb, r_stb } = 4'h2 when done reg [7:0] cmd_addr; always @(posedge i_clk) cmd_addr = wr_addr - { r_word[32:31], r_word[29:24] }; // Let's also calculate the address, in case this is a compressed // address word reg [24:0] r_addr; always @(posedge i_clk) case(r_word[32:30]) 3'b000: r_addr <= { 19'h0, r_word[29:24] }; 3'b010: r_addr <= { 13'h0, r_word[29:18] }; 3'b100: r_addr <= { 7'h0, r_word[29:12] }; 3'b110: r_addr <= { 1'h0, r_word[29: 6] }; 3'b001: r_addr <= { {(19){ r_word[29]}}, r_word[29:24] }; 3'b011: r_addr <= { {(13){ r_word[29]}}, r_word[29:18] }; 3'b101: r_addr <= { {( 7){ r_word[29]}}, r_word[29:12] }; 3'b111: r_addr <= { {( 1){ r_word[29]}}, r_word[29: 6] }; endcase wire [31:0] w_addr; assign w_addr = { {(7){r_addr[24]}}, r_addr }; reg [9:0] rd_len; always @(posedge i_clk) if (~r_word[34]) rd_len <= 10'h01 + { 6'h00, r_word[33:31] }; else rd_len <= 10'h08 + { 1'b0, r_word[33:31], r_word[29:24] }; // Clock three, read the table value // { o_stb, r_stb } = 4'h4 when done // Maintaining ... // r_word (clock 1) // r_addr, rd_len (clock 2) reg [31:0] cword; always @(posedge i_clk) cword <= compression_tbl[cmd_addr]; // Pipeline the strobe signal to create an output strobe, 3 clocks later reg [2:0] r_stb; initial r_stb = 0; always @(posedge i_clk) r_stb <= { r_stb[1:0], i_stb }; // Clock four, now that the table value is valid, let's set our output // word. // { o_stb, r_stb } = 4'h8 when done always @(posedge i_clk) o_stb <= r_stb[2]; // Maintaining ... // r_word (clock 1) // r_addr, rd_len (clock 2) // cword (clock 3) // Any/all of these can be pipelined for faster operation // However, speed is really limited by the speed of the I/O port. At // it's fastest, it's 1 bit per clock, 48 clocks per codeword therefore, // thus ... things will hold still for much longer than just 5 clocks. always @(posedge i_clk) if (r_word[35:30] == 6'b101110) o_word <= r_word; else casez(r_word[35:30]) // Set address from something compressed ... unsigned 6'b001??0: o_word <= { 4'h0, w_addr[31:0] }; // Set a new address as a signed offset from the last (set) one // (The last address is kept further down the chain, // we just mark here that the address is to be set // relative to it, and by how much.) 6'b001??1: o_word <= { 3'h1, w_addr[31:30], 1'b1, w_addr[29:0]}; // Write a value to the bus, with the value given from our // codeword table 6'b010???: o_word <= { 3'h3, cword[31:30], r_word[30], cword[29:0] }; // Read, highly compressed length (1 word) 6'b10????: o_word <= { 5'b11000, r_word[30], 20'h00, rd_len }; // Read, two word (3+9 bits) length 6'b11????: o_word <= { 5'b11000, r_word[30], 20'h00, rd_len }; default: o_word <= r_word; endcase endmodule
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