Add condition based MethodFilter

[lekcyjna123]

This MR is the first fragment of #395 to port to the trunk. Here I extend MethodFilter with possibility to use condition under the hood to ignore situations, where method is not ready and condition is false. This has the caveats that resulting filter is single_caller so both versions should coexistence.

[lekcyjna123]

A remark to remember is that the usage of validate_arguments is not possible in MethodFilter, because this feature cause blocking of method, if the condition is not fulfilled, what cause the blocking of the calling transaction.

[piotro888]

Approved, but maybe if it doesn't cause any logic penalty this:

               with condition(m, nonblocking=True) as branch:
                    with branch(cond):
                        m.d.comb += ret.eq(self.target(m, arg))

would be cleaner? (nonblocking=True to automatically generate empty default condition - equivalent to ~cond)

[tilk]

The conditions are mutually exclusive - maybe priority=False should be used?

Or remove the second branch and use nonblocking=True, as @piotro888 suggested. Right now you use both exclusivity and transaction priorities - do you see any advantage of this, or is this accidental?

[tilk]

I'm waiting with merge until this is resolved.

[lekcyjna123]

We can not use nonblocking=True here. The condition class doesn't use two state logic. We have:

• True and ready
• False and ready
• Not ready

If the cond=1 and target is not ready, then with nonblocking=True the transaction will execute and so the whole method will execute, which will be wrong because the data instead of being forwarded will be dropped.

I added priority=False, this shouldn't impact the logic.

[tilk]

Address the review comment.