Identity link in tweedie

Hi there,
I'm using the tweedie distribution package and I cant figure out how to 
run a model using an identity link. I know I can use a log link by 
having link.power=0 and I think identity would be link.power=1, but I'm 
not sure. Furthermore when I try running it with link.power=1 it 
requires starting values which I cant manage to give appropriately so 
I'm not sure if its actually an identity link its using. I can't find 
this info on the help page and I was wondering if somebody could give me 
a hand.
Thanks a lot.
Cheers,
Cristina.