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// Copyright (c) 2006-2011 by Lattice Semiconductor Corporation
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// Open Source License Agreement.
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// FILE DETAILS
// Project : LatticeMico32
// File : lm32_shifter.v
// Title : Barrel shifter
// Dependencies : lm32_include.v
// Version : 6.1.17
// : Initial Release
// Version : 7.0SP2, 3.0
// : No Change
// Version : 3.1
// : No Change
// =============================================================================
`include "lm32_include.v"
/////////////////////////////////////////////////////
// Module interface
/////////////////////////////////////////////////////
module lm32_shifter (
// ----- Inputs -------
clk_i,
rst_i,
stall_x,
direction_x,
sign_extend_x,
operand_0_x,
operand_1_x,
// ----- Outputs -------
shifter_result_m
);
/////////////////////////////////////////////////////
// Inputs
/////////////////////////////////////////////////////
input clk_i; // Clock
input rst_i; // Reset
input stall_x; // Stall instruction in X stage
input direction_x; // Direction to shift
input sign_extend_x; // Whether shift is arithmetic (1'b1) or logical (1'b0)
input [`LM32_WORD_RNG] operand_0_x; // Operand to shift
input [`LM32_WORD_RNG] operand_1_x; // Operand that specifies how many bits to shift by
/////////////////////////////////////////////////////
// Outputs
/////////////////////////////////////////////////////
output [`LM32_WORD_RNG] shifter_result_m; // Result of shift
wire [`LM32_WORD_RNG] shifter_result_m;
/////////////////////////////////////////////////////
// Internal nets and registers
/////////////////////////////////////////////////////
reg direction_m;
reg [`LM32_WORD_RNG] left_shift_result;
reg [`LM32_WORD_RNG] right_shift_result;
reg [`LM32_WORD_RNG] left_shift_operand;
wire [`LM32_WORD_RNG] right_shift_operand;
wire fill_value;
wire [`LM32_WORD_RNG] right_shift_in;
integer shift_idx_0;
integer shift_idx_1;
/////////////////////////////////////////////////////
// Combinational Logic
/////////////////////////////////////////////////////
// Select operands - To perform a left shift, we reverse the bits and perform a right shift
always @(*)
begin
for (shift_idx_0 = 0; shift_idx_0 < `LM32_WORD_WIDTH; shift_idx_0 = shift_idx_0 + 1)
left_shift_operand[`LM32_WORD_WIDTH-1-shift_idx_0] = operand_0_x[shift_idx_0];
end
assign right_shift_operand = direction_x == `LM32_SHIFT_OP_LEFT ? left_shift_operand : operand_0_x;
// Determine fill value for right shift - Sign bit for arithmetic shift, or zero for logical shift
assign fill_value = (sign_extend_x == `TRUE) && (direction_x == `LM32_SHIFT_OP_RIGHT)
? operand_0_x[`LM32_WORD_WIDTH-1]
: 1'b0;
// Determine bits to shift in for right shift or rotate
assign right_shift_in = {`LM32_WORD_WIDTH{fill_value}};
// Reverse bits to get left shift result
always @(*)
begin
for (shift_idx_1 = 0; shift_idx_1 < `LM32_WORD_WIDTH; shift_idx_1 = shift_idx_1 + 1)
left_shift_result[`LM32_WORD_WIDTH-1-shift_idx_1] = right_shift_result[shift_idx_1];
end
// Select result
assign shifter_result_m = direction_m == `LM32_SHIFT_OP_LEFT ? left_shift_result : right_shift_result;
/////////////////////////////////////////////////////
// Sequential Logic
/////////////////////////////////////////////////////
// Perform right shift
always @(posedge clk_i `CFG_RESET_SENSITIVITY)
begin
if (rst_i == `TRUE)
begin
right_shift_result <= {`LM32_WORD_WIDTH{1'b0}};
direction_m <= `FALSE;
end
else
begin
if (stall_x == `FALSE)
begin
right_shift_result <= {right_shift_in, right_shift_operand} >> operand_1_x[`LM32_SHIFT_RNG];
direction_m <= direction_x;
end
end
end
endmodule
