feat: Complete CSR/privileged/exception interrupt path and fill in strict acceptance tests

- Refactor trap/CSR data path in the Core, unified with trap_ctrl interface to drive CSR update and return process
- Improve critical paths for exception/interrupt handling: ecall, illegal, load fault, external interrupt, mret/sret return
- Adjust pipeline stage registers with flush/stall coordination, fix residual control signal issues in trap scenarios
- Enhance decode and related pipeline module behavior consistency, fill in missing control signal propagation across registers
- Expand core integration testing, add trap/interrupt scenarios and CLI dispatch that can be executed per case
- Extend CSR unit test coverage: read/write semantics, privilege switching, delegation and nested returns, illegal access protection, etc.
- Register new core scenario cases in CTest to form a regression-capable P2 strict acceptance suite

Verification:

- Build passed
- Full CTest passed (22/22)

1 files changed, 7 insertions, 2 deletions

diff --git a/rv64cpu/tb/unit/tb_decoder.cc b/rv64cpu/tb/unit/tb_decoder.cc
index aa6788c..25a3d69 100644
--- a/rv64cpu/tb/unit/tb_decoder.cc
+++ b/rv64cpu/tb/unit/tb_decoder.cc
@@ -39,7 +39,8 @@ static int fail_count = 0;
         } \
     } while(0)
 
-void decode(Vdecoder* dut, uint32_t instr, const char* name) {
+void decode(Vdecoder* dut, uint32_t instr, const char* name, uint8_t priv_mode = 3) {
+    dut->priv_mode = priv_mode & 0x3;
     dut->instr = instr;
     dut->eval();
     test_count++;
@@ -233,6 +234,10 @@ int main(int argc, char** argv) {
     CHECK(dut, reg_write_en, 1,  "CSRRW");
     CHECK(dut, illegal_instr,0,  "CSRRW");
 
+    decode(dut, 0x300110F3, "CSRRW x1, mstatus, x2 (U-mode)", 0);
+    CHECK(dut, illegal_instr,1,  "CSRRW U-mode illegal");
+    CHECK(dut, is_csr,       0,  "CSRRW U-mode is_csr cleared");
+
     // 20. ECALL
     //     all-zero fields + opcode=1110011
     decode(dut, 0x00000073, "ECALL");
@@ -256,7 +261,7 @@ int main(int argc, char** argv) {
 
     // 23. SRET
     //     funct7=0001000 rs2=00010 rs1=00000 funct3=000 rd=00000 op=1110011
-    decode(dut, 0x10200073, "SRET");
+    decode(dut, 0x10200073, "SRET", 1);
     CHECK(dut, is_sret,      1,  "SRET");
     CHECK(dut, reg_write_en, 0,  "SRET");