Has write_analog changed since firmware 1.7.9

I had some code for controlling a servo, the code used PMW to send a micro second timed pulse.
I was using firmware 1.7.9, but recently have upgraded Mu and uflash to use the latest version 1.9.2-34 v1.0.0-rc.2
```
def write_us(self, period):
duty=int(period * 1024 * self.frequency / 1000000)
self.pin.write_analog(duty)
self.pin.write_digital(0)
```
which worked and the servo would move. Now there's nothing until a sleep is added between write_analog and write_digital.