added stepping functionality to the debugger

riscemu/CPU.py

@@ -25,6 +25,7 @@ class CPU:
         self.exit = False
         self.exit_code = 0
         self.conf = conf
+        self.active_debug = False # if a debugging session is currently runnign
 
         # setup MMU, registers and syscall handlers
         self.mmu = MMU(conf)
@@ -66,7 +67,30 @@ class CPU:
 
         self.__run()
 
-    def __run(self):
+    def continue_from_debugger(self, verbose=True):
+        """
+        dalled from the debugger to continue running
+        """
+        self.__run(verbose)
+
+    def step(self):
+        if self.exit:
+            print(FMT_CPU + "Program exited with code {}".format(self.exit_code) + FMT_NONE)
+        else:
+            try:
+                self.cycle += 1
+                ins = self.mmu.read_ins(self.pc)
+                print("Running instruction {} from 0x{:08X}".format(ins, self.pc))
+                self.pc += 1
+                self.__run_instruction(ins)
+            except LaunchDebuggerException:
+                print(FMT_CPU + "[CPU] Returning to debugger!" + FMT_NONE)
+            except RiscemuBaseException as ex:
+                self.pc -= 1
+                print(ex.message())
+
+
+    def __run(self, verbose=False):
         if self.pc <= 0:
             return False
         ins = None
@@ -74,14 +98,22 @@ class CPU:
             while not self.exit:
                 self.cycle += 1
                 ins = self.mmu.read_ins(self.pc)
+                if verbose:
+                    print(FMT_CPU + "   Running 0x{:08X}:{} {}".format(self.pc, FMT_NONE, ins))
                 self.pc += 1
                 self.__run_instruction(ins)
         except RiscemuBaseException as ex:
-            print(FMT_ERROR + "[CPU] excpetion caught at 0x{:08X}: {}:".format(self.pc-1, ins) + FMT_NONE)
+            if not isinstance(ex, LaunchDebuggerException):
-            print("      " + ex.message())
+                print(FMT_ERROR + "[CPU] excpetion caught at 0x{:08X}: {}:".format(self.pc-1, ins) + FMT_NONE)
+                print(ex.message())
+                self.pc -= 1
+
+            if self.active_debug:
+                print(FMT_CPU + "[CPU] Returning to debugger!" + FMT_NONE)
+                return
             if self.conf.debug_on_exception:
                 launch_debug_session(self, self.mmu, self.regs,
-                                     "Exception encountered, launching debug:".format(self.pc-1))
+                                     "Exception encountered, launching debug:")
 
         print()
         print(FMT_CPU + "Program exited with code {}".format(self.exit_code) + FMT_NONE)

riscemu/Exceptions.py

@@ -134,3 +134,9 @@ class NumberFormatException(RiscemuBaseException):
             self.__class__.__name__,
             self.msg
         )
+
+
+# this exception is not printed and simply signals that an interactive debugging session is
+class LaunchDebuggerException(RiscemuBaseException):
+    def message(self):
+        return ""

riscemu/debug.py

@@ -1,31 +1,46 @@
 import typing
+from .Registers import Registers
 if typing.TYPE_CHECKING:
     from . import *
 
 
 def launch_debug_session(cpu: 'CPU', mmu: 'MMU', reg: 'Registers', prompt=""):
-    if not cpu.conf.debug_instruction:
+    if not cpu.conf.debug_instruction or cpu.active_debug:
         return
     import code
     import readline
     import rlcompleter
 
-    # setup some aliases
+    cpu.active_debug = True
+
+    # setup some aliases:
     registers = reg
     regs = reg
     memory = mmu
     mem = mmu
     syscall_interface = cpu.syscall_int
 
+    # setup helper functions:
     def dump(what, *args, **kwargs):
         if isinstance(what, Registers):
             regs.dump(*args, **kwargs)
         else:
             mmu.dump(what, *args, **kwargs)
 
+    def ins():
+        print("Current instruction at 0x{:08X}:".format(cpu.pc))
+        return mmu.read_ins(cpu.pc)
+
+    def cont(verbose=True):
+        cpu.continue_from_debugger(verbose)
+
+    def step():
+        cpu.step()
+
     sess_vars = globals()
     sess_vars.update(locals())
 
     readline.set_completer(rlcompleter.Completer(sess_vars).complete)
     readline.parse_and_bind("tab: complete")
-    code.InteractiveConsole(sess_vars).interact(banner=prompt, exitmsg="Resuming simulation")
+    code.InteractiveConsole(sess_vars).interact(banner=prompt, exitmsg="Exiting debugger")
+    cpu.active_debug = False

riscemu/instructions/RV32I.py

@@ -271,7 +271,10 @@ class RV32I(InstructionSet):
 
     def instruction_sbreak(self, ins: 'LoadedInstruction'):
         ASSERT_LEN(ins.args, 0)
-        launch_debug_session(self.cpu, self.mmu, self.regs, "Debug instruction encountered at 0x{:08X}".format(self.pc))
+        if self.cpu.active_debug:
+            print("Debug instruction encountered at 0x{:08X}".format(self.pc-1))
+            raise LaunchDebuggerException()
+        launch_debug_session(self.cpu, self.mmu, self.regs, "Debug instruction encountered at 0x{:08X}".format(self.pc-1))
 
     def instruction_nop(self, ins: 'LoadedInstruction'):
         ASSERT_LEN(ins.args, 0)