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Simplified shifter right input

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This commit is contained in:
David Harris 2021-12-18 10:25:40 -08:00
parent d97d34ee32
commit 7fb4213751
2 changed files with 23 additions and 25 deletions
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6
wally-pipelined/src/ieu/alu.sv
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@ -33,7 +33,6 @@ module alu #(parameter WIDTH=32) (
output logic [WIDTH-1:0] Sum);
logic [WIDTH-1:0] CondInvB, Shift, SLT, SLTU, FullResult;
logic Right;
logic Carry, Neg;
logic LT, LTU;
logic Overflow;
@ -51,9 +50,8 @@ module alu #(parameter WIDTH=32) (
assign {Carry, Sum} = A + CondInvB + {{(WIDTH-1){1'b0}}, SubArith};
// Shifts
assign Right = Funct3[2]; // sra or srl
shifter sh(A, B[`LOG_XLEN-1:0], Right, SubArith, W64, Shift);
shifter sh(.A, .Amt(B[`LOG_XLEN-1:0]), .Right(Funct3[2]), .Arith(SubArith), .W64, .Y(Shift));
// condition code flags based on add/subtract output
// Overflow occurs when the numbers being added have the same sign
// and the result has the opposite sign

42
wally-pipelined/src/ieu/shifter.sv
View File

@ -26,10 +26,10 @@
`include "wally-config.vh"
module shifter (
input logic [`XLEN-1:0] a,
input logic [`LOG_XLEN-1:0] amt,
input logic right, arith, w64,
output logic [`XLEN-1:0] y);
input logic [`XLEN-1:0] A,
input logic [`LOG_XLEN-1:0] Amt,
input logic Right, Arith, W64,
output logic [`XLEN-1:0] Y);
logic [2*`XLEN-2:0] z, zshift;
logic [`LOG_XLEN-1:0] amttrunc, offset;
@ -42,34 +42,34 @@ module shifter (
generate
if (`XLEN==32) begin:shifter // RV32
always_comb // funnel mux
if (right)
if (arith) z = {{31{a[31]}}, a};
else z = {31'b0, a};
else z = {a, 31'b0};
assign amttrunc = amt; // shift amount
if (Right)
if (Arith) z = {{31{A[31]}}, A};
else z = {31'b0, A};
else z = {A, 31'b0};
assign amttrunc = Amt; // shift amount
end else begin:shifter // RV64
always_comb // funnel mux
if (w64) begin // 32-bit shifts
if (right)
if (arith) z = {64'b0, {31{a[31]}}, a[31:0]};
else z = {95'b0, a[31:0]};
else z = {32'b0, a[31:0], 63'b0};
if (W64) begin // 32-bit shifts
if (Right)
if (Arith) z = {64'b0, {31{A[31]}}, A[31:0]};
else z = {95'b0, A[31:0]};
else z = {32'b0, A[31:0], 63'b0};
end else begin
if (right)
if (arith) z = {{63{a[63]}}, a};
else z = {63'b0, a};
else z = {a, 63'b0};
if (Right)
if (Arith) z = {{63{A[63]}}, A};
else z = {63'b0, A};
else z = {A, 63'b0};
end
assign amttrunc = w64 ? {1'b0, amt[4:0]} : amt; // 32 or 64-bit shift
assign amttrunc = W64 ? {1'b0, Amt[4:0]} : Amt; // 32 or 64-bit shift
end
endgenerate
// opposite offset for right shfits
assign offset = right ? amttrunc : ~amttrunc;
assign offset = Right ? amttrunc : ~amttrunc;
// funnel operation
assign zshift = z >> offset;
assign y = zshift[`XLEN-1:0];
assign Y = zshift[`XLEN-1:0];
endmodule