From 2d4a23664382c3192bb492218ce01c07353ca118 Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 21 Nov 2018 14:38:42 +0000
Subject: [PATCH] converting cpu_fetch_stage to migen

---
 cpu_fetch_stage.py | 110 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 cpu_fetch_stage.py

diff --git a/cpu_fetch_stage.py b/cpu_fetch_stage.py
new file mode 100644
index 0000000..a120573
--- /dev/null
+++ b/cpu_fetch_stage.py
@@ -0,0 +1,110 @@
+"""
+/*
+ * Copyright 2018 Jacob Lifshay
+ *
+ * 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.
+ *
+ */
+"""
+
+from migen import *
+from migen.fhdl import verilog
+
+from riscvdefs import *
+from cpudefs import *
+
+reset_vector = 32'hXXXXXXXX;
+mtvec = 32'hXXXXXXXX;
+
+class CPUFetchStage(Module):
+    def __init__(self):
+        self.clk = ClockSignal()
+        self.reset = ResetSignal()
+        #output [31:2] memory_interface_fetch_address,
+        self.memory_interface_fetch_address = Signal(32)[2:]
+        #input [31:0] memory_interface_fetch_data,
+        self.memory_interface_fetch_data = Signal(32)
+        self.memory_interface_fetch_valid = Signal()
+        input `fetch_action fetch_action,
+        input [31:0] target_pc,
+        self.output_pc = Signal(32, reset=reset_vector)
+        self.output_instruction = Signal(32)
+        output reg `fetch_output_state output_state
+        
+        self.comb += [
+            self.cd_sys.clk.eq(self.clk),
+            self.cd_sys.rst.eq(self.reset)
+        ]
+
+        fetch_pc = Signal(32, reset=reset_vector)
+        
+        self.sync += output_pc.eq((fetch_action == `fetch_action_wait) ? output_pc : fetch_pc);
+        
+        memory_interface_fetch_address = fetch_pc[31:2];
+
+        initial output_pc <= reset_vector;
+        initial output_state <= `fetch_output_state_empty;
+        
+        delayed_instruction = Signal(32, reset=0);
+        delayed_instruction_valid = Signal(reset=0);
+        
+        self.sync += delayed_instruction.eq(output_instruction)
+        
+        assign output_instruction = delayed_instruction_valid ? delayed_instruction : memory_interface_fetch_data;
+        
+        self.sync += delayed_instruction_valid.eq(fetch_action == `fetch_action_wait)
+        
+        always @(posedge clk or posedge reset) begin
+            if(reset) begin
+                output_state <= `fetch_output_state_empty;
+            end
+            else begin
+                case(fetch_action)
+                `fetch_action_default,
+                `fetch_action_ack_trap: begin
+                    if(memory_interface_fetch_valid) begin
+                        fetch_pc <= fetch_pc + 4;
+                        output_state <= `fetch_output_state_valid;
+                    end
+                    else begin
+                        fetch_pc <= mtvec;
+                        output_state <= `fetch_output_state_trap;
+                    end
+                end
+                `fetch_action_fence: begin
+                    fetch_pc <= output_pc + 4;
+                    output_state <= `fetch_output_state_empty;
+                end
+                `fetch_action_jump: begin
+                    fetch_pc <= target_pc;
+                    output_state <= `fetch_output_state_empty;
+                end
+                `fetch_action_error_trap,
+                `fetch_action_noerror_trap: begin
+                    fetch_pc <= mtvec;
+                    output_state <= `fetch_output_state_empty;
+                end
+                `fetch_action_wait: begin
+                    fetch_pc <= fetch_pc;
+                    output_state <= `fetch_output_state_valid;
+                end
+                endcase
+            end
+        end
+    endmodule
-- 
2.30.2