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70 lines
3.2 KiB
Systemverilog
70 lines
3.2 KiB
Systemverilog
///////////////////////////////////////////
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// tlbmixer.sv
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//
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// Written: David Harris and kmacsaigoren@hmc.edu 7 June 2021
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// Modified:
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//
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//
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// Purpose: Takes two page numbers and replaces segments of the first page
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// number with segments from the second, based on the page type.
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// NOTE: this DOES NOT include the 12 bit offset, which is the same no matter the translation mode or page type.
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//
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// Documentation: RISC-V System on Chip Design Chapter 8
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//
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// A component of the CORE-V-WALLY configurable RISC-V project.
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//
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// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
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//
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// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
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//
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// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
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// except in compliance with the License, or, at your option, the Apache License version 2.0. You
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// may obtain a copy of the License at
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//
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// https://solderpad.org/licenses/SHL-2.1/
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//
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// Unless required by applicable law or agreed to in writing, any work distributed under the
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// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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////////////////////////////////////////////////////////////////////////////////////////////////
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`include "wally-config.vh"
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module tlbmixer (
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input logic [`VPN_BITS-1:0] VPN,
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input logic [`PPN_BITS-1:0] PPN,
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input logic [1:0] HitPageType,
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input logic [11:0] Offset,
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input logic TLBHit,
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output logic [`PA_BITS-1:0] TLBPAdr
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);
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localparam EXTRA_BITS = `PPN_BITS - `VPN_BITS;
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logic [`PPN_BITS-1:0] ZeroExtendedVPN;
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logic [`PPN_BITS-1:0] PageNumberMask;
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logic [`PPN_BITS-1:0] PPNMixed;
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// produce PageNumberMask with 1s where virtual page number bits should be untranslaetd for superpages
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if (`XLEN == 32)
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// kilopage: 22 bits of PPN, 0 bits of VPN
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// megapage: 12 bits of PPN, 10 bits of VPN
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mux2 #(22) pnm(22'h000000, 22'h0003FF, HitPageType[0], PageNumberMask);
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else
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// kilopage: 44 bits of PPN, 0 bits of VPN
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// megapage: 35 bits of PPN, 9 bits of VPN
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// gigapage: 26 bits of PPN, 18 bits of VPN
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// terapage: 17 bits of PPN, 27 bits of VPN
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mux4 #(44) pnm(44'h00000000000, 44'h000000001FF, 44'h0000003FFFF, 44'h00007FFFFFF, HitPageType, PageNumberMask);
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// merge low segments of VPN with high segments of PPN decided by the pagetype.
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assign ZeroExtendedVPN = {{EXTRA_BITS{1'b0}}, VPN}; // forces the VPN to be the same width as PPN.
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assign PPNMixed = PPN | ZeroExtendedVPN & PageNumberMask; //
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//mux2 #(1) mixmux[`PPN_BITS-1:0](ZeroExtendedVPN, PPN, PageNumberMask, PPNMixed);
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//assign PPNMixed = (ZeroExtendedVPN & ~PageNumberMask) | (PPN & PageNumberMask);
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// Output the hit physical address if translation is currently on.
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// Provide physical address of zero if not TLBHits, to cause segmentation error if miss somehow percolated through signal
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mux2 #(`PA_BITS) hitmux('0, {PPNMixed, Offset}, TLBHit, TLBPAdr); // set PA to 0 if TLB misses, to cause segementation error if this miss somehow passes through system
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endmodule
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