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[/] [amber/] [trunk/] [hw/] [vlog/] [amber25/] [a25_barrel_shift.v] - Rev 78
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////////////////////////////////////////////////////////////////// // // // Barrel Shifter for Amber 25 Core // // // // This file is part of the Amber project // // http://www.opencores.org/project,amber // // // // Description // // Provides 32-bit shifts LSL, LSR, ASR and ROR // // // // Author(s): // // - Conor Santifort, csantifort.amber@gmail.com // // // ////////////////////////////////////////////////////////////////// // // // Copyright (C) 2011 Authors and OPENCORES.ORG // // // // This source file may be used and distributed without // // restriction provided that this copyright statement is not // // removed from the file and that any derivative work contains // // the original copyright notice and the associated disclaimer. // // // // This source file is free software; you can redistribute it // // and/or modify it under the terms of the GNU Lesser General // // Public License as published by the Free Software Foundation; // // either version 2.1 of the License, or (at your option) any // // later version. // // // // This source is distributed in the hope that it will be // // useful, but WITHOUT ANY WARRANTY; without even the implied // // warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR // // PURPOSE. See the GNU Lesser General Public License for more // // details. // // // // You should have received a copy of the GNU Lesser General // // Public License along with this source; if not, download it // // from http://www.opencores.org/lgpl.shtml // // // ////////////////////////////////////////////////////////////////// module a25_barrel_shift ( input i_clk, input [31:0] i_in, input i_carry_in, input [7:0] i_shift_amount, // uses 8 LSBs of Rs, or a 5 bit immediate constant input i_shift_imm_zero, // high when immediate shift value of zero selected input [1:0] i_function, output [31:0] o_out, output o_carry_out, output o_stall ); wire [31:0] quick_out; wire quick_carry_out; wire [31:0] full_out; wire full_carry_out; reg [31:0] full_out_r = 'd0; reg full_carry_out_r = 'd0; reg use_quick_r = 1'd1; assign o_stall = (|i_shift_amount[7:2]) & use_quick_r; assign o_out = use_quick_r ? quick_out : full_out_r; assign o_carry_out = use_quick_r ? quick_carry_out : full_carry_out_r; // Capture the result from the full barrel shifter in case the // quick shifter gives the wrong value always @(posedge i_clk) begin full_out_r <= full_out; full_carry_out_r <= full_carry_out; use_quick_r <= !o_stall; end // Full barrel shifter a25_shifter #( .FULL_BARREL (1) ) u_a25_shifter_full ( .i_in ( i_in ), .i_carry_in ( i_carry_in ), .i_shift_amount ( i_shift_amount ), .i_shift_imm_zero ( i_shift_imm_zero ), .i_function ( i_function ), .o_out ( full_out ), .o_carry_out ( full_carry_out ) ); // Quick barrel shifter a25_shifter #( .FULL_BARREL ( 0 ) ) u_a25_shifter_quick ( .i_in ( i_in ), .i_carry_in ( i_carry_in ), .i_shift_amount ( i_shift_amount ), .i_shift_imm_zero ( i_shift_imm_zero ), .i_function ( i_function ), .o_out ( quick_out ), .o_carry_out ( quick_carry_out ) ); endmodule
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