[CSR] adding virtual csr registers

riscemu/priv/CSR.py

@@ -41,6 +41,11 @@ class CSR:
     All Control and Status Registers are stored here
     """
 
+    virtual_regs: Dict[int, Callable[[], int]]
+    """
+    list of virtual CSR registers, with values computed on read
+    """
+
     name_to_addr: Dict[str, int] = {
         'mstatus': 0x300,
         'misa': 0x301,
@@ -56,7 +61,9 @@ class CSR:
         'mhartid': 0xF14,
         'time': 0xc01,
         'timeh': 0xc81,
-        'halt': 0x789
+        'halt': 0x789,
+        'mtimecmp': 0x780,
+        'mtimecmph': 0x781,
     }
     """
     Translation for named registers
@@ -67,6 +74,7 @@ class CSR:
     def __init__(self):
         self.regs = defaultdict(lambda: 0)
         self.listeners = defaultdict(lambda: (lambda x, y: None))
+        #TODO: implement write masks (bitmasks which control writeable bits in registers
 
     def set(self, addr: Union[str, int], val: int):
         addr = self._addr_to_name(addr)
@@ -75,15 +83,18 @@ class CSR:
         self.listeners[addr](self.regs[addr], val)
         self.regs[addr] = val
 
-    def get(self, addr: Union[str, int]):
+    def get(self, addr: Union[str, int]) -> int:
         addr = self._addr_to_name(addr)
         if addr is None:
             return
+        if addr in self.virtual_regs:
+            return self.virtual_regs[addr]()
         return self.regs[addr]
 
     def set_listener(self, addr: Union[str, int], listener: Callable[[int, int], None]):
         addr = self._addr_to_name(addr)
         if addr is None:
+            print("unknown csr address name: {}".format(addr))
             return
         self.listeners[addr] = listener
 
@@ -107,7 +118,7 @@ class CSR:
         new_val = erased | (val << off)
         self.set('mstatus', new_val)
 
-    def get_mstatus(self, name):
+    def get_mstatus(self, name) -> int:
         size = 2 if name in MSTATUS_LEN_2 else 1
         off = MSTATUS_OFFSETS[name]
         mask = (2**size - 1) << off
@@ -134,3 +145,14 @@ class CSR:
                 return None
             return self.name_to_addr[addr]
         return addr
+
+    def virtual_register(self, addr: Union[str, int]):
+        addr = self._addr_to_name(addr)
+        if addr is None:
+            print("unknown csr address name: {}".format(addr))
+
+        def inner(func: Callable[[], int]):
+            self.virtual_regs[addr] = func
+            return func
+
+        return inner