WFI: Reacquire control of the core in the debugger after it executes a WFI instruction.

A new gdb_stop_evt event was added, triggered when the debugger issues
a stop request. The thread now waits on wfi_evt or gdb_stop_evt
(SystemC OR event list). After waking, it checks whether gdb_stop_evt triggered;
if so, it exits the loop immediately.

Author: quic-prateek

src/iss/debugger/riscv_target_adapter.h

@@ -80,6 +80,8 @@ template <typename ARCH> class riscv_target_adapter : public target_adapter_base
      avail buf is 1 */
     status read_registers(std::vector<uint8_t>& data, std::vector<uint8_t>& avail) override;
 
+    status trigger_debugger_stop_event() override;
+
     /* Write all registers. buf is 4-byte aligned and it is in target
      byte order */
     status write_registers(const std::vector<uint8_t>& data) override;
@@ -183,6 +185,10 @@ template <typename ARCH> status riscv_target_adapter<ARCH>::current_thread_query
     return Ok;
 }
 
+template <typename ARCH> status riscv_target_adapter<ARCH>::trigger_debugger_stop_event() {
+    core->cancel_wait();
+    return Ok;
+}
 template <typename ARCH> status riscv_target_adapter<ARCH>::read_registers(std::vector<uint8_t>& data, std::vector<uint8_t>& avail) {
     CPPLOG(TRACE) << "reading target registers";
     data.clear();

src/sysc/core2sc_adapter.h

@@ -244,13 +244,24 @@ template <typename PLAT> class core2sc_adapter : public PLAT, public sc2core_if
     void wait_until(uint64_t flags) {
         SCCDEBUG(owner->hier_name()) << "Sleeping until interrupt";
         PLAT::wait_until(flags);
+        wfi_inst.store(true, std::memory_order_relaxed);
         std::function<void(void)> f = [this]() {
             while((this->csr[iss::arch::mip] & this->csr[iss::arch::mie]) == 0) {
-                sc_core::wait(this->wfi_evt);
+                sc_core::wait(this->wfi_evt | this->debugger_stop_evt);
+                bool is_debugger_stop_evt = this->debugger_stop_evt.triggered();
+                if(is_debugger_stop_evt) break;
             }
             SCCINFO(this->owner->hier_name()) << "Got WFI event";
         };
         owner->exec_on_sysc(f);
+        wfi_inst.store(false, std::memory_order_relaxed);
+    }
+
+    void cancel_wait() {
+        if(wfi_inst.load(std::memory_order_relaxed) == true) {
+            SCCDEBUG(owner->hier_name()) << "Trigger debugger stop event";
+            this->debugger_stop_evt.notify(sc_core::SC_ZERO_TIME);
+        }
     }
 
 private:
@@ -338,8 +349,10 @@ template <typename PLAT> class core2sc_adapter : public PLAT, public sc2core_if
     util::LoggerDelegate log_delegate;
     util::LoggerDelegate disass_delegate;
     sc_core::sc_event wfi_evt;
+    sc_core::sc_event debugger_stop_evt;
     unsigned to_host_wr_cnt = 0;
     bool first{true};
+    std::atomic<bool> wfi_inst{false};
     mutex_t sync_mtx;
 };
 } // namespace sysc