Avalon MM Burst Read/Writes

[gbowers4]

There is a current issue & PR raised relating to Avalon MM burst read/writes - #44.

After implementing these changes the Avalon Memory Model presents a scheduler error - "Write to object {} was scheduled during a read-only sync phase.", similar to that in #8.

The issue is with 337 async def _waitrequest(self): both lines 344 and 349 can cause the above error.

It can be fixed similarly by adding await ReadWrite().

[gbowers4]

However - does this present a fundamental error with assigning values? It is my understanding that scheduler phases should only be a concern when using setimmediatevalue(), otherwise the scheduler should store values and set them at the end of a time step?