There is no problem with you asking about an i2c problem with an ARM processor from my point of view.

A Repeated Start Condition is only a Start Condition that happens without a preceding Stop. Some controllers use a different hardware command. All hardware implementations will recognise the difference in their state machine and return the appropriate status.

However it would be helpful if you answered my questions about your code and what return values you get for i2c_start() and i2c_write(slave) calls or equivalent.

My guess is that your slave is not ACKing before you set the register address.

David.

p.s. if you supply the information then you will probably get the solution within an hour or two. If your code is in C then it will apply to any controller.