The book Kaliyugada Kalpataru, written by Raja Gururajacharya, (who was the son from the poorvashrama of Sri Raghavendra Swami), is a complete biography of Sri Raghavandra Swami.
While writing my answer for a question asking about the previous incarnations of Sri Raghavendra Swami, I searched online, but I was not able to find it.
Is there an online copy of the book available?