Recently Luigi Tarenga wanted to do some work on developing RTL-SDR drivers, so he emailed Rafael Micro requesting some additional documentation about the chip. Usually previous requests to Rafael Micro for such information seem to have gone unanswered, but this time it seems they have decided to publicly released the Register description document for the R820T2 chip.
Previously the R820T datasheet was leaked/released to the public, but the information in the datasheet did not help much with driver development. This register description document describes the function and configuration bits for the registers on the chip, and may be useful for people wanting to develop better drivers for the RTL-SDR.
We have uploaded a copy on our server here.