set attributes' rand_mode in pre_randomize does not work

[qijiuliushisan]

import vsc

@vsc.randobj
class A():
    def __init__(self):
        self.a=vsc.rand_bit_t(16)
        self.b=vsc.rand_bit_t(20)
    
    def pre_randomize(self):
        with vsc.raw_mode():
            self.a.rand_mode=False
obj=A()
obj.randomize()
print(obj.a,obj.b)

obj.a is expected to be 0. But the output showed that obj.a had been randomized.

[alwilson]

Before pre_randomize() is called set_used_rand() is called on each field_model. This sets is_used_rand on each field depending on rand_mode and other factors. Disabling rand_mode in pre_randomize() doesn't change the is_used_rand field, which is the field that controls field randomization later.

Setting rand_mode in raw_mode() in turn calls the rand_mode() setter function. One possible fix would be to set is_used_rand here as well, which would probably do the right thing if setting rand_mode to False, but could enable a disabled field if rand_mode gets set to True? We could also allow only setting it to False here to avoid the False->True scenario.

pyvsc/src/vsc/types.py

Lines 414 to 416 in de14431

	@rand_mode.setter
	def rand_mode(self, v):
	self._int_field_info.model.rand_mode = bool(v)

Another option is to call set_used_rand() again after call pre_randomize() to update is_used_rand accordingly. Maybe that's cleaner?

        # First, invoke pre_randomize on all elements
        for fm in field_model_l:
            fm.pre_randomize()
            f.set_used_rand(True, 0)

@mballance Any preference or insight? I can fix it up and add a testcase for it.