From ee768c51d4e95b1cabfc876e4a832f3cea5da15a Mon Sep 17 00:00:00 2001
From: Graham Edgecombe <gpe@grahamedgecombe.com>
Date: Sun, 3 Dec 2017 13:53:52 +0000
Subject: [PATCH] Add FENCE and FENCE.I instructions

Both are currently NOPs as the implementation is currently in-order and
has separate instruction and data memories.
---
 rv32_decode.sv  | 8 ++++++++
 rv32_opcodes.sv | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/rv32_decode.sv b/rv32_decode.sv
index 6fcde9a..83dec52 100644
--- a/rv32_decode.sv
+++ b/rv32_decode.sv
@@ -449,6 +449,14 @@ module rv32_decode (
                 alu_src2_out <= RV32_ALU_SRC2_REG;
                 rd_writeback_out <= 1;
             end
+            {RV32_OPCODE_MISC_MEM, RV32_FUNCT3_MISC_MEM_FENCE, RV32_FUNCT7_ANY}: begin
+                /* FENCE */
+                valid_out <= 1;
+            end
+            {RV32_OPCODE_MISC_MEM, RV32_FUNCT3_MISC_MEM_FENCE_I, RV32_FUNCT7_ANY}: begin
+                /* FENCE.I */
+                valid_out <= 1;
+            end
         endcase
     end
 endmodule
diff --git a/rv32_opcodes.sv b/rv32_opcodes.sv
index ef6dd25..cafee94 100644
--- a/rv32_opcodes.sv
+++ b/rv32_opcodes.sv
@@ -42,6 +42,9 @@ localparam RV32_FUNCT3_OP_SRL_SRA = 3'b101;
 localparam RV32_FUNCT3_OP_OR      = 3'b110;
 localparam RV32_FUNCT3_OP_AND     = 3'b111;
 
+localparam RV32_FUNCT3_MISC_MEM_FENCE   = 3'b000;
+localparam RV32_FUNCT3_MISC_MEM_FENCE_I = 3'b001;
+
 localparam RV32_FUNCT7_ANY  = 7'b???????;
 localparam RV32_FUNCT7_ZERO = 7'b0000000;