Wikipedia
SystemRDL
The SystemRDL language, supported by the SPIRIT Consortium, was specifically designed to describe and implement a wide variety of control status registers. Using SystemRDL, developers can automatically generate and synchronize register views for specification, hardware design, software development, verification, and documentation.
SystemRDL is the only open source text based descriptive language that focuses exclusively on registers. SystemRDL1.0 had some limitations which are now being worked on by a group under the auspices of Accellera. SystemRDL2.0 will have support for verification based properties like Constraints, Coverage, HDL_PATH etc.