fix known bugs

6 files changed, 68 insertions, 21 deletions

diff --git a/rv64cpu/rtl/core/decoder.sv b/rv64cpu/rtl/core/decoder.sv
index 585a018..c948646 100644
--- a/rv64cpu/rtl/core/decoder.sv
+++ b/rv64cpu/rtl/core/decoder.sv
@@ -80,7 +80,7 @@ module decoder
     assign opcode   = instr[6:0];
     assign rd_addr  = instr[11:7];
     assign funct3   = instr[14:12];
-    assign rs1_addr = instr[19:15];
+    assign rs1_addr = (opcode == OPCODE_LUI) ? 5'b00000 : instr[19:15];
     assign rs2_addr = instr[24:20];
     assign funct7   = instr[31:25];
 
diff --git a/rv64cpu/rtl/core/ex_mem_reg.sv b/rv64cpu/rtl/core/ex_mem_reg.sv
index 4fcf140..a8182aa 100644
--- a/rv64cpu/rtl/core/ex_mem_reg.sv
+++ b/rv64cpu/rtl/core/ex_mem_reg.sv
@@ -107,7 +107,7 @@ module ex_mem_reg
 );
 
     always_ff @(posedge clk) begin
-        if (rst || flush_en) begin
+        if (rst) begin
             mem_alu_result    <= '0;
             mem_branch_taken  <= '0;
             mem_branch_target <= '0;
@@ -138,6 +138,28 @@ module ex_mem_reg
             mem_is_fence      <= '0;
             mem_is_fence_i    <= '0;
 
+        end else if (flush_en) begin
+            // Critical control signals must be zeroed out
+            mem_branch_taken  <= '0;
+            mem_is_load       <= '0;
+            mem_is_store      <= '0;
+            mem_mem_size      <= '0;
+            mem_reg_write_en  <= '0;
+            mem_rd_addr       <= '0;
+            mem_wb_sel        <= '0;
+
+            // Exceptions and system control
+            mem_is_csr        <= '0;
+            mem_csr_op        <= '0;
+            mem_illegal_instr <= '0;
+            mem_is_ecall      <= '0;
+            mem_is_ebreak     <= '0;
+            mem_is_mret       <= '0;
+            mem_is_sret       <= '0;
+            mem_is_wfi        <= '0;
+            mem_is_sfence_vma <= '0;
+            mem_is_fence      <= '0;
+            mem_is_fence_i    <= '0;
         end else if (~stall_en) begin
              mem_alu_result    <= ex_alu_result;
              mem_branch_taken  <= ex_branch_taken;
diff --git a/rv64cpu/rtl/core/ex_stage.sv b/rv64cpu/rtl/core/ex_stage.sv
index 0991b50..48d4833 100644
--- a/rv64cpu/rtl/core/ex_stage.sv
+++ b/rv64cpu/rtl/core/ex_stage.sv
@@ -42,17 +42,17 @@ module ex_stage
     output logic [XLEN-1:0]    ex_branch_target
 );
 
-    logic [XLEN-1:0]    alumux_a;
-    logic [XLEN-1:0]    alumux_b;
+    logic [XLEN-1:0]    alu_mux_a;
+    logic [XLEN-1:0]    alu_mux_b;
     logic [XLEN-1:0]    alu_operand_a;
     logic [XLEN-1:0]    alu_operand_b;
     logic [XLEN-1:0]    alu_raw_result;
-    logic               bu_branch_taken;
+    logic               branch_unit_taken;
 
     // -------------
     // ALU Input Multiplexers (MUX)
-    assign alumux_a = (ex_alu_src1_sel == 1'b1) ? ex_pc : ex_rs1_rdata;
-    assign alumux_b = (ex_alu_src2_sel == 1'b1) ? ex_imm : ex_rs2_rdata;
+    assign alu_mux_a = (ex_alu_src1_sel == 1'b1) ? ex_pc : ex_rs1_rdata;
+    assign alu_mux_b = (ex_alu_src2_sel == 1'b1) ? ex_imm : ex_rs2_rdata;
     
     // -------------
     // RV64 Word Operation (32-bit) Pre-conditioning
@@ -62,21 +62,21 @@ module ex_stage
         if (ex_is_word_op) begin
             // Shift operations require specific 32-bit extension forms
             if (ex_alu_op == ALU_SRA)
-                alu_operand_a = { {32{alumux_a[31]}}, alumux_a[31:0] }; // Sign extend for arithmetic shift
+                alu_operand_a = { {32{alu_mux_a[31]}}, alu_mux_a[31:0] }; // Sign extend for arithmetic shift
             else if (ex_alu_op == ALU_SRL)
-                alu_operand_a = { 32'b0, alumux_a[31:0] };              // Zero extend for logical shift
+                alu_operand_a = { 32'b0, alu_mux_a[31:0] };              // Zero extend for logical shift
             else
-                alu_operand_a = alumux_a;                               // ADDW/SUBW/SLLW don't care about upper bits
+                alu_operand_a = alu_mux_a;                               // ADDW/SUBW/SLLW don't care about upper bits
             
             // RV32 shift amount is strictly 5 bits (0-31), ignoring bit 5 which might be set in 64-bit registers
             if (ex_alu_op == ALU_SLL || ex_alu_op == ALU_SRL || ex_alu_op == ALU_SRA)
-                alu_operand_b = { 59'b0, alumux_b[4:0] };
+                alu_operand_b = { 59'b0, alu_mux_b[4:0] };
             else
-                alu_operand_b = alumux_b;
+                alu_operand_b = alu_mux_b;
         end else begin
             // 64-bit operations pass through unchanged
-            alu_operand_a = alumux_a;
-            alu_operand_b = alumux_b;
+            alu_operand_a = alu_mux_a;
+            alu_operand_b = alu_mux_b;
         end
     end
 
@@ -96,7 +96,7 @@ module ex_stage
         .branch_op    (ex_branch_op),
         .operand_a    (ex_rs1_rdata),
         .operand_b    (ex_rs2_rdata),
-        .branch_taken (bu_branch_taken)
+        .branch_taken (branch_unit_taken)
     );
 
     // ------------- 
@@ -109,6 +109,6 @@ module ex_stage
     // Branch Target Calculation
     assign ex_branch_target = alu_raw_result & ~64'b1;
 
-    assign ex_branch_taken  = ex_is_jump | (ex_is_branch & bu_branch_taken);
+    assign ex_branch_taken  = ex_is_jump | (ex_is_branch & branch_unit_taken);
 
 endmodule
diff --git a/rv64cpu/rtl/core/id_ex_reg.sv b/rv64cpu/rtl/core/id_ex_reg.sv
index 7c780ee..e88ce17 100644
--- a/rv64cpu/rtl/core/id_ex_reg.sv
+++ b/rv64cpu/rtl/core/id_ex_reg.sv
@@ -113,7 +113,7 @@ module id_ex_reg
 );
 
     always_ff @(posedge clk) begin
-        if (rst || flush_en) begin
+        if (rst) begin
             ex_pc            <= '0;
             ex_rs1_rdata     <= '0;
             ex_rs2_rdata     <= '0;
@@ -144,6 +144,31 @@ module id_ex_reg
             ex_is_sfence_vma <= '0;
             ex_is_fence      <= '0;
             ex_is_fence_i    <= '0;
+        end else if (flush_en) begin
+            ex_alu_op        <= ALU_ADD; // NOP is effectively ADD x0, x0, 0
+            ex_alu_src1_sel  <= '0;
+            ex_alu_src2_sel  <= '0;
+            ex_is_word_op    <= '0;
+            ex_is_branch     <= '0;
+            ex_branch_op     <= BRANCH_EQ;
+            ex_is_jump       <= '0;
+            ex_is_load       <= '0;
+            ex_is_store      <= '0;
+            ex_mem_size      <= '0;
+            ex_reg_write_en  <= '0; // VERY IMPORTANT: Do not write to regfile on NOP
+            ex_rd_addr       <= '0;
+            ex_wb_sel        <= '0;
+            ex_is_csr        <= '0;
+            ex_csr_op        <= '0;
+            ex_illegal_instr <= '0;
+            ex_is_ecall      <= '0;
+            ex_is_ebreak     <= '0;
+            ex_is_mret       <= '0;
+            ex_is_sret       <= '0;
+            ex_is_wfi        <= '0;
+            ex_is_sfence_vma <= '0;
+            ex_is_fence      <= '0;
+            ex_is_fence_i    <= '0;
         end else if (~stall_en) begin
             ex_pc            <= id_pc;
             ex_rs1_rdata     <= id_rs1_rdata;
diff --git a/rv64cpu/tb/unit/tb_ex_mem_reg.cc b/rv64cpu/tb/unit/tb_ex_mem_reg.cc
index 4ad2494..db1fe8b 100644
--- a/rv64cpu/tb/unit/tb_ex_mem_reg.cc
+++ b/rv64cpu/tb/unit/tb_ex_mem_reg.cc
@@ -150,7 +150,7 @@ int main(int argc, char** argv) {
     
     tick(dut);
 
-    check(dut->mem_pc == 0x0, "Flush_Clears_PC");
+    check(dut->mem_pc == 0x80003000, "Flush_Maintains_PC");
     check(dut->mem_branch_taken == 0, "Flush_Clears_BranchTaken");
     check(dut->mem_reg_write_en == 0, "Flush_Clears_RegWrite"); 
     check(dut->mem_is_store == 0, "Flush_Clears_StoreEn");     
@@ -168,7 +168,7 @@ int main(int argc, char** argv) {
     dut->ex_branch_taken = 1;
     tick(dut);
 
-    check(dut->mem_pc == 0x0, "Flush_Overrides_Stall_PC");
+    check(dut->mem_pc == 0x80005000, "Flush_Overrides_Stall_PC");
     check(dut->mem_branch_taken == 0, "Flush_Overrides_Stall_BranchTaken");
     check(dut->mem_reg_write_en == 0, "Flush_Overrides_Stall_RegWrite");
     check(dut->mem_is_store == 0, "Flush_Overrides_Stall_Store");
diff --git a/rv64cpu/tb/unit/tb_id_ex_reg.cc b/rv64cpu/tb/unit/tb_id_ex_reg.cc
index 2248564..d9cc329 100644
--- a/rv64cpu/tb/unit/tb_id_ex_reg.cc
+++ b/rv64cpu/tb/unit/tb_id_ex_reg.cc
@@ -148,7 +148,7 @@ int main(int argc, char** argv) {
     
     tick(dut);
 
-    check(dut->ex_pc == 0x0, "Flush_Clears_PC");
+    check(dut->ex_pc == 0x80003000, "Flush_Maintains_PC");
     check(dut->ex_reg_write_en == 0, "Flush_Clears_RegWrite"); 
     check(dut->ex_is_store == 0, "Flush_Clears_StoreEn");     
     check(dut->ex_is_branch == 0, "Flush_Clears_BranchEn");
@@ -165,7 +165,7 @@ int main(int argc, char** argv) {
     dut->id_pc = 0x80006000;
     tick(dut);
 
-    check(dut->ex_pc == 0x0, "Flush_Overrides_Stall_PC");
+    check(dut->ex_pc == 0x80005000, "Flush_Overrides_Stall_PC");
     check(dut->ex_reg_write_en == 0, "Flush_Overrides_Stall_RegWrite");
 
     std::cout << "----------------------------------" << std::endl;