Instruction fetching stage unit and test

1 files changed, 111 insertions, 0 deletions

diff --git a/rv64cpu/tb/unit/tb_if_stage.cc b/rv64cpu/tb/unit/tb_if_stage.cc
new file mode 100644
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+++ b/rv64cpu/tb/unit/tb_if_stage.cc
@@ -0,0 +1,111 @@
+//     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: tb/unit/tb_if_stage.cc
+// Description: IF Stage unit test
+
+#include <iostream>
+#include <iomanip>
+#include <cstdint>
+#include <cassert>
+#include <verilated.h>
+#include "Vif_stage.h"
+
+void tick(Vif_stage* dut) {
+    dut->clk = 0;
+    dut->eval();
+    dut->clk = 1;
+    dut->eval();
+    dut->clk = 0;
+    dut->eval();
+}
+
+void check_pc(uint64_t expected_pc, uint64_t actual_pc, const char* test_name) {
+    if (expected_pc == actual_pc) {
+        std::cout << "\033[32m[PASS] " << test_name << " | PC = 0x" << std::hex << actual_pc << "\033[0m" << std::dec << std::endl;
+    } else {
+        std::cout << "\033[31m[FAIL] " << test_name << " | Expected PC = 0x" << std::hex << expected_pc << " | Got PC = 0x" << actual_pc << "\033[0m" << std::dec << std::endl;
+        assert(false);
+    }
+}
+
+int main(int argc, char** argv) {
+    Verilated::commandArgs(argc, argv);
+    Vif_stage* dut = new Vif_stage;
+
+    std::cout << "----------------------------------" << std::endl;
+    std::cout << "        IF Stage Test" << std::endl;
+    std::cout << "----------------------------------" << std::endl;
+
+    // --- 1. Init / Reset ---
+    dut->stall_en = 0;
+    dut->ex_branch_taken = 0;
+    dut->ex_branch_target = 0;
+    
+    dut->rst = 1;
+    tick(dut);
+    dut->rst = 0;
+    check_pc(0x80000000ULL, dut->if_pc, "Reset_Boot_Address");
+
+    // --- 2. Normal Execution (PC + 4) ---
+    tick(dut);
+    check_pc(0x80000004ULL, dut->if_pc, "Normal_Increment_1");
+    tick(dut);
+    check_pc(0x80000008ULL, dut->if_pc, "Normal_Increment_2");
+
+    // --- 3. Pipeline Stall ---
+    dut->stall_en = 1;
+    tick(dut);
+    check_pc(0x80000008ULL, dut->if_pc, "Stall_Maintains_PC");
+    tick(dut);
+    check_pc(0x80000008ULL, dut->if_pc, "Stall_Maintains_PC_Again");
+    
+    // Release Stall
+    dut->stall_en = 0;
+    tick(dut);
+    check_pc(0x8000000CULL, dut->if_pc, "Release_Stall_Normal_Increment");
+
+    // --- 4. Branch Taken ---
+    dut->ex_branch_taken = 1;
+    dut->ex_branch_target = 0x80000100ULL;
+    tick(dut);
+    check_pc(0x80000100ULL, dut->if_pc, "Branch_Taken_Updates_PC");
+
+    // Return to normal
+    dut->ex_branch_taken = 0;
+    tick(dut);
+    check_pc(0x80000104ULL, dut->if_pc, "Post_Branch_Normal_Increment");
+
+    // --- 5. Stall and Branch simultaneous priority ---
+    // If a branch is taken but the pipeline is stalled, the PC should freeze.
+    // However, if the stall clears later, the branch target should theoretically be taken. 
+    // In our RV64 simple pipeline design, stall_en freezes the PC reg completely. 
+    dut->ex_branch_taken = 1;
+    dut->ex_branch_target = 0x80000200ULL;
+    dut->stall_en = 1;
+    tick(dut);
+    check_pc(0x80000104ULL, dut->if_pc, "Stall_Overrides_Branch_Target_Load");
+    
+    dut->stall_en = 0;
+    tick(dut);
+    check_pc(0x80000200ULL, dut->if_pc, "Branch_Target_Loaded_After_Stall_Clears");
+
+    std::cout << "----------------------------------" << std::endl;
+    std::cout << "\033[32mAll tests passed!\033[0m" << std::endl;
+    std::cout << "----------------------------------" << std::endl;
+
+    delete dut;
+    return 0;
+}
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