Instruction fetching stage unit and test

1 files changed, 60 insertions, 0 deletions

diff --git a/rv64cpu/rtl/core/if_stage.sv b/rv64cpu/rtl/core/if_stage.sv
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+//     Richard CPU
+//     Copyright (C) 2026  Richard Qin
+
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General Public License as published by
+//     the Free Software Foundation, either version 3 of the License, or
+//     (at your option) any later version.
+
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General Public License for more details.
+
+//     You should have received a copy of the GNU General Public License
+//     along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+// File path: rtl/core/if_stage.sv
+// Description: Instruction Fetching Stage, includes PC registers and next-state PC calculation logic
+
+module if_stage 
+    import rv64_pkg::*;
+(
+    input logic                clk,
+    input logic                rst,
+
+    // Pipeline Control Signals (from Hazard Unit & EX Stage)
+    input logic                stall_en,       // Freeze PC (stall), 0: Normal operation
+    input logic                ex_branch_taken,   // Branch taken signal from EX Stage
+    input logic [XLEN-1:0]     ex_branch_target, // Branch target address from EX Stage
+    
+    output logic [XLEN-1:0]    if_pc
+);
+
+    // PC Register
+    logic [XLEN-1:0] pc_reg;
+
+    // Combinational logic signal: the PC value to be written in the next clock cycle
+    logic [XLEN-1:0] next_pc;
+
+    always_comb begin
+        if (ex_branch_taken) begin
+            next_pc = ex_branch_target;
+        end else begin
+            next_pc = pc_reg + 64'd4;
+        end
+    end
+
+    // Sequential Logic: Update PC Register
+    always_ff @(posedge clk) begin
+        if (rst) begin
+            pc_reg <= 64'h0000_0000_8000_0000;
+        end else if (~stall_en) begin
+            pc_reg <= next_pc;
+        end
+    end
+    
+    // Output wiring
+    assign if_pc = pc_reg;
+    
+endmodule