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dataMem_mask_gen.v
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/*
Authored 2018-2019, Ryan Voo.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
* Redistributions of source code must retain the above
copyright notice, this list of conditions and the following
disclaimer.
* Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials
provided with the distribution.
* Neither the name of the author nor the names of its
contributors may be used to endorse or promote products
derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
/*
* mask for loads/stores in data memory
*/
module sign_mask_gen(func3, sign_mask);
input [2:0] func3;
output [3:0] sign_mask;
reg [2:0] mask;
/*
* sign - for LBU and LHU the sign bit is 0, indicating read data should be zero extended, otherwise sign extended
* mask - for determining if the load/store operation is on word, halfword or byte
*
* TODO - a Karnaugh map should be able to describe the mask without case, the case is for reading convenience
*/
always @(*) begin
case(func3[1:0])
2'b00: mask = 3'b001; // byte only
2'b01: mask = 3'b011; // halfword
2'b10: mask = 3'b111; // word
default: mask = 3'b000; // should not happen for loads/stores
endcase
end
assign sign_mask = {(~func3[2]), mask};
endmodule