lrdp-v2: register.py: add support for setting the register value

The Register class currently can't handle setting the `value'
attribute. Fix this. Also add a `zero' convenience method for zeroing
out a register.

After adding the following doctest:

    >>> abc.value = 0
    >>> abc.value
    0

but before fixing __setattr__, I get:

    **********************************************************************
    File "register.py", line 42, in __main__.Register
    Failed example:
        abc.value = 0
    Exception raised:
        Traceback (most recent call last):
          File "/usr/lib/python2.7/doctest.py", line 1289, in __run
            compileflags, 1) in test.globs
          File "<doctest __main__.Register[10]>", line 1, in <module>
            abc.value = 0
          File "register.py", line 106, in __setattr__
            raise AttributeError
        AttributeError
    **********************************************************************
    File "register.py", line 43, in __main__.Register
    Failed example:
        abc.value
    Expected:
        0
    Got:
        49
    **********************************************************************
    1 items had failures:
       2 of  20 in __main__.Register
    ***Test Failed*** 2 failures.

After the fix in __setattr__, all tests pass successfully.

Change-Id: I6d39261b139aae0def58f38a4291baad651b10e3

linux-ramdump-parser-v2/register.py

@@ -39,6 +39,15 @@ class Register(object):
     >>> abc.other = 0x3
     >>> hex(abc.value)
     '0x31'
+    >>> abc.value = 0
+    >>> abc.value
+    0
+    >>> abc.value = 42
+    >>> abc.value
+    42
+    >>> abc.zero()
+    >>> abc.value
+    0
 
     You can also overlay fields on top of each other without problems:
 
@@ -84,6 +93,9 @@ class Register(object):
         """
         self._regs[field] = bitrange
 
+    def zero(self):
+        object.__setattr__(self, 'value', 0)
+
     def __dir__(self):
         return self.__dict__.keys() + self._regs.keys()
 
@@ -96,6 +108,9 @@ class Register(object):
         return bitops.bvalsel(msb, lsb, self.value)
 
     def __setattr__(self, name, newvalue):
+        if name == 'value':
+            object.__setattr__(self, 'value', newvalue)
+            return
         if name not in self._regs:
             raise AttributeError
         if self.value is None: