Begin hardware page table walker

wally-pipelined/src/ebu/ahblite.sv

@@ -89,8 +89,8 @@ module ahblite (
     else          BusState <= #1 NextBusState;
 
   always_comb 
-    case (BusState) 
-      IDLE: if      (MemReadM)   NextBusState = MEMREAD;  // Memory has pirority over instructions
+    case (BusState)
+      IDLE: if      (MemReadM)   NextBusState = MEMREAD;  // Memory has priority over instructions
             else if (MemWriteM)  NextBusState = MEMWRITE;
             else if (InstrReadF) NextBusState = INSTRREAD;
             else                 NextBusState = IDLE;

wally-pipelined/src/ebu/pagetablewalker.sv

@@ -0,0 +1,102 @@
+///////////////////////////////////////////
+// ahblite.sv
+//
+// Written: tfleming@hmc.edu 2 March 2021
+// Modified: 
+//
+// Purpose: Page Table Walker
+//          Part of the Memory Management Unit (MMU)
+// 
+// A component of the Wally configurable RISC-V project.
+// 
+// Copyright (C) 2021 Harvey Mudd College & Oklahoma State University
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, 
+// modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software 
+// is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS 
+// BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT 
+// OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+///////////////////////////////////////////
+
+`include "wally-config.vh"
+
+module pagetablewalker (
+  input  logic             clk, reset,
+
+  input  logic [`XLEN-1:0] satp,
+
+  input  logic             TLBMissF,
+  input  logic [`XLEN-1:0] TranslationVAdr,
+
+  input  logic             HCLK, HRESETn,
+
+  input  logic             HREADY,
+
+  output logic [`XLEN-1:0] PageTableEntryF,
+  output logic             TranslationComplete
+);
+
+  /*
+  generate
+    if (`XLEN == 32) begin
+      logic Sv_Mode       = satp[31]
+    end else begin
+      logic Sv_Mode [3:0] = satp[63:60]
+    end
+  endgenerate
+  */
+
+  logic Sv_Mode = satp[31];
+  logic BasePageTablePPN [21:0] = satp[21:0];
+
+  logic VPN1 [9:0] = TranslationVAdr[31:22];
+  logic VPN0 [9:0] = TranslationVAdr[21:12]; // *** could optimize by not passing offset?
+
+  logic TranslationPAdr [33:0];
+
+  typedef enum {IDLE, LEVEL1, LEVEL0, LEAF, FAULT} statetype;
+  statetype WalkerState, NextWalkerState;
+
+  always_ff @(posedge HCLK, negedge HRESETn)
+    if (~HRESETn) WalkerState <= #1 IDLE;
+    else          WalkerState <= #1 NextWalkerState;
+  
+  always_comb begin
+    NextWalkerState = 'X;
+    case (WalkerState)
+      IDLE:   if      (TLBMissM)             NextWalkerState = LEVEL1;
+              else                           NextWalkerState = IDLE;
+      LEVEL1: if      (HREADY && ValidEntry) NextWalkerState = LEVEL0;
+              else if (HREADY)               NextWalkerState = FAULT;
+              else                           NextWalkerState = LEVEL1;
+      LEVEL2: if      (HREADY && ValidEntry) NextWalkerState = LEAF;
+              else if (HREADY)               NextWalkerState = FAULT;
+              else                           NextWalkerState = LEVEL2;
+      LEAF:                                  NextWalkerState = IDLE;
+    endcase
+  end
+
+  always_ff @(posedge HCLK, negedge HRESETn)
+    if (~HRESETn) begin
+      TranslationPAdr <= '0;
+      PageTableEntryF <= '0;
+      TranslationComplete <= '0;
+    end else begin
+      // default values
+      case (NextWalkerState)
+        LEVEL1: TranslationPAdr <= {BasePageTablePPN, VPN1, 2'b00};
+        LEVEL2: TranslationPAdr <= {CurrentPPN, VPN0, 2'b00};
+        LEAF:   PageTableEntryF <= CurrentPageTableEntry;
+                TranslationComplete <= '1;
+    end
+
+  assign #1 Translate = (NextWalkerState = LEVEL1);
+
+
+endmodule