can you explain me use of Had I

Question

I want to know the structure of "Hardly had I slept when the telephone rang" or can we use hardly I had slept when the telephone rang.

Answer 1

This sentence is making use of Inversion. The same sentence without Inversion would be:

I had hardly slept when the telephone rang.

which means the same thing as

Hardly had I slept when the telephone rang.